Sunday, April 15, 2012

Unit Compilation 3


Unit Compilation 3



Ch.5 the Skeletal System

Table of Contents

5.1 The skeletal system consists of connective tissue

            a. Bones are the hard elements of the skeleton

            b. Bone contains living cells

            c. Ligaments hold bones together

            d. Cartilage lends support

5.3 Mature bone undergoes remodeling and repair

            a. Bones can change in shape, size, and strength

            b. Bone cells are regulated by hormones

            c. Bones undergo repair

5.4 The skeleton protects, supports, and permits movement

            a. The axial skeleton forms the midline of the body

                        1. The skull: Cranial and facial bones

                        2. The vertebral column: The body’s main axis

                        3. The ribs and sternum: Protecting the chest cavity

            b. The appendicular skeleton: Pectoral girdle, pelvic girdle, and limbs

                        1. The pectoral girdle lends flexibility to the upper limbs

                        2. The pelvic girdle supports the body

5.5 Joints form connections between bones

            a. Joints vary from immovable to freely movable

            b. Ligaments, tendons, and muscles strengthen and stabilize joints




 5.1 The skeletal system consists of connective tissue


            The skeletal system is made up of three types of connective tissue:



1.      Bones- the hard elements of the skeleton

2.      Ligaments- bind bones together

3.      Cartilage-reduces friction in the joints



Here is a picture of a knee joint that shows all three types of connective tissue.













5.1a Bones are the hard elements of the skeleton



Bones consist of living cells surrounded by extracellular deposits of calcium minerals. Bones store minerals and produce cellular components of blood (Red Blood Cells, White Blood Cells and Platelets). The mass of bones, which consists of nonliving extracellular crystals of calcium minerals, is what gives bones their hard, rigid appearance and feel (Johnson 2012).



Bones have five important functions (Oellers, Online Presentation, 2012):



1.      Support soft internal organs like the lungs, liver and spleen.

2.      Protects the soft internal organs.

3.      The attachment of our bones to muscle is what makes it possible for us to move.

4.      Blood Cell Formation- cells in certain bones are the only source of new red and white blood cells and platelets for blood. Without this production we would die.

5.      Mineral Storage of Calcium and Phosphate bones store these two important minerals.



5.1b Bone contains living cells



Bones structure is made up of a hard inorganic matrix of calcium salts (Oellers, Online Presentation, 2012).



Bone is classified as either compact or spongy.





http://www.google.com/imgres?imgurl=http://cooter.k12.mo.us/MrWalls/Bio2/chap%252045/Chapter%252045%2520%2520Bones%2520and%2520Muscles_files/image028.jpg&imgrefurl=http://cooter.k12.mo.us/MrWalls/Bio2/chap%252045/Chapter%252045%2520%2520Bones%2520and%2520Muscles.htm&h=541&w=845&sz=110&tbnid=MLIUELZR05pAaM:&tbnh=72&tbnw=113&prev=/search%3Fq%3Dpictures%2Bof%2Bhuman%2Bstructures%2Bof%2Bbones%26tbm%3Disch%26tbo%3Du&zoom=1&q=pictures+of+human+structures+of+bones&docid=d_pKeBuCYMpHyM&hl=en&sa=X&ei=DFRxT_a6GpSCtgeAntD5Dw&ved=0CGkQ9QEwDg&dur=497, Retrieved April 10, 2012.



Compact bones form the shaft, cover each end (epiphysis) of the bone and contain yellow bone marrow in the central cavity in the shaft (diaphysis). Yellow bone marrow is primarily fat that is used for energy. A tough layer of connective tissue, the periosteum, which contains specialized bone-forming cells, covers the outer surface of the bone. Inside each epiphysis is spongy bone. Compact bone is made up largely of extracellular deposits of calcium phosphate, surrounding living cells called osteocytes (mature bone cells).

Osteocytes are arranged in rings in cylindrical structures called osteons (haversian system).

Osteocytes near the center of an osteon, receive nutrients by diffusion from blood vessels that pass through a central canal (Haversian canal). Haversian canals are also called central organs (Oellers, Online Presentation, 2012).

As bone develops and becomes hard the osteocytes become trapped in hollow chambers called lacunae (Johnson 2012). The osteocytes remain in direct contact with each other by thin canals called canalicule. Within the canaliculi, gap junctions join extensions of the cells cytoplasm of adjacent osteocytes together (Johnson 2012). Gap junctions are channels that permit the movement of ions, water, and other molecules between two adjacent cells (Johnson 2012). Osteocytes are supplied with nutrients by the exchange of nutrients across this gap junction, even though most osteocytes are not located near a blood vessel. Waste products produced by the osteocytes are exchanged in the opposite direction and are removed from the bone by the blood vessels (Johnson 2012).



Spongy bone is less dense than compact bone, allowing bones to be light and strong. Spongy bone is composed of calcium minerals and living cells that are strong trabreculae (little beams). An example of spongy bone is the upper arms and legs (the humerus and femur). The spaces between the trabeculae in the upper arms and legs are filled with red bone marrow, which is responsible for the production of red and white blood cells and platelets.




5.1c Ligaments hold bones together



Ligaments attach bone to bone (Johnson 2012). Ligaments are comprised of connective tissue (closely packed collagen fibers oriented in the same direction with a few fibroblasts in between) that holds bones together. Fibroblasts are cells that produce and secrete the proteins that compose collagen, elastic, and reticular fibers (Johnson 2012). Ligaments give strength to certain joints, while still allowing movement of the bones in relation to each other. When damaged, ligaments are slow to heal because they have very few living cells and a poor blood supply.



5.1d Cartilage lends support



Cartilage contains fibers of collagen or elastin in a ground substance of water and other materials (Johnson 2012). Cartilage needs to be flexible to support the joints under pressure when movement is necessary. In a moveable joint, bone surfaces are covered by a layer of smooth cartilage and lubricated with fluid, to reduce friction and wear (Johnson 2012).



There are three types of cartilage:



1.      Fibrocartilage mainly made up of collagen fibers arranged in thick bundles. Fibrocartilage allows the joints to withstand pressure and tension well. Example of a joint made up of fibrocartilage is the knee joint called the menisci.

2.      Hyaline cartilage is smooth, almost grassy. Hyaline cartilage is thin collagen fibers (Johnson 2012). This type of cartilage forms the embryonic structures that later become the bones and covers the ends of mature bones in joints to create a smooth, low-friction surface.

3.      Elastic cartilage is made up of elastin fibers. This type of cartilage is very flexible and aids in forming the outer ear and to the epiglottis (a flap of tissue that covers the larynx during swallowing) (Johnson 2012).



5.3  Mature bone undergoes remodeling and repair



Bones change throughout one’s lifetime. Bone is a dynamic tissue that undergoes constant replacement, remodeling, and repair (Johnson 2012).

A bone called an osteoclast is a bone-dissolving cell. This cell remodels and repairs injured bones by dissolving bone when the bone needs to be renewed and allows new cells to form. This cell cuts through mature bone tissue, dissolving the hydroxyapatite (calcium phosphate (Oellers, Online Presentation, 2012)) and digesting the osteoid matrix in their path. This means that when a bone is fractured or injured the bone is now curved and misshaped. Over time bone is deposited on the inside curvature and removed by osteoclasts from the outside curvature. This result in a bone matched to its previous shape.




Osteoclasts and the Mechanism of Bone Resorption. A: Light micrograph and B: electron micrograph of an osteoclast, demonstrating the ruffled border and numerous nuclei. C: Osteoclastic resorption. The osteoclast forms a sealing zone via integrin mediated attachment to specific peptide sequences within the bone matrix, forming a sealed compartment between the cell and the bone surface. This compartment is acidified such that an optimal pH is reached for lysosomal enzyme activity and bone resorption.



5.3a Bones can change in shape, size and strength

If constant remodeling is done repeatedly, this can affect the shape of a bone. Electrical currents stimulate the bone-forming osteoblasts caused by repeated compression stress on a bone such as jogging.

Having dense, stronger bones will help in reducing bone injuries. Having a regular program of any weight-bearing exercise such as weight lifting will increase your muscular strength. Osteoporosis is a bone disorder that can cause the bone to become brittle and fracture easily. Science Daily (April 25, 2012) wrote an article that says research shows that osteoporosis results from hundreds of genes, although body weight, build and gender play a role as well. Researchers are now trying to develop an anti-osteoporosis drug.

Homeostasis is important in bone structure and depends on the balance of osteoclasts and osteoblasts.  Osteoporosis is a result of losing bone mass due to an imbalance of osteoclasts and osteoblasts.


5.3b Bone cells are regulated by hormones


Hormones that maintain calcium homeostasis are regulated by the activity of osteoblasts and osteoclasts.

These hormones are:



·         Parathyroid (PTH) removes calcium from bone. PTH stimulates the osteoclasts to secrete more bone dissolving enzymes when blood levels of calcium fall below a given point.



·         Calcitonin adds calcium to the bone if calcium levels rise. Calcitonin stimulates osteoblast activity causing calcium and phosphate to be removed from blood and deposited in bone (Johnson 2012).



5.3c Bones undergo repair


When your break or fracture a bone the blood vessels supplying the bone bleed into the area, producing a mass of clotted blood called a hematoma (Johnson 2012). The repair process begins when fibroblasts become chondroblasts (cartilage forming cells laid down first, then the osteoblasts which are young bone forming cells) and together they produce a tough callus (formed of protein and cartilage) formation between the two broken ends of the bone. The osteoclasts begin to remove dead fragments of the original bone and the blood cells of the hematoma. The osteoblasts then deposit osteoid matix converting the callus into bone. The repair process can take weeks to months depending on a person’s age.


5.4  The skeleton protects, supports, and permits movement


The human body has 206 bones and the connective tissues that hold them together make up the skeleton.



Bones can be classified into four types based on shape:



1.      Long bones are cylindrical with growth heads. The epiphysis is at either end and the long bone is covered by articular cartilage. Long bones include the limbs and fingers.

2.      Short bones are cube shaped with movements that are more complex. They include the wrist bones.

3.      Flat bones protect the internal organs and include the skull, ribs, scapula (shoulder blade), sternum (breastbones) and pelvic girdle (Oellers online presentation 2012).

4.      Irregular bones include shapes that do not fit into the other categories such as the hip, vertebra and some facial bones.







 The skeleton has three important functions:



1.      It is the structural framework for support of the soft organs.

2.      It protects certain organs from physical injury for example the brain is enclosed within the bones of the skull, and the heart and lungs are protected by a bony cage consisting of ribs, sternum and vertebrae (Johnson 2012).

3.      The way that the bony elements of the skeleton are joined together at joints, permits the body to move like the hands, feet, legs and arms.



The skeleton is organized into the axial skeleton and the appendicular skeleton






5.4a The axial skeleton forms the midline of the body


The axial skeleton is the skull, sternum, ribs and vertebral column (Johnson 2012).



5.4a, 1 The skull: Cranial and facial bones





The skull consists of approximately two dozen bones that protect the brain and form the structure of the face (Johnson 2012). The cranial bones are flat bones in the skull that enclose and protect the brain. Starting at the front of the skull are the frontal bone that makes up the forehead and the upper ridges of the eye sockets. At the upper left and right sides of the skull are the two parietal bones, the two temporal bones are the lower left and right side that is has an opening into the ear canal for sound to travel to the eardrum. The facial bones compose the front of the skull. On each side of the nose are the two-maxilla bones, which form part of the eye socket and contain the sockets that anchor the upper row of teeth. The sphenoid bone is in between the frontal and the temporal bones. The sphenoid bone forms the back of both eye sockets. The ethmoid bone contributes to the eye sockets and supports the nose. The nose is made up of cartilage and other connective tissue. The nasal cavity is the part of the space formed by the maxillary and nasal bones. The nasal bones are beneath the upper bridge of the nose only. The lacrimal bones at the inner eye sockets have tiny openings so tear ducts can drain tears from the eye sockets into the nasal cavity. The mandible or lower jaw contains sockets that house the lower row of teeth and attaches to the temporal bone by a joint so that the jaw is able to move allowing us to talk and chew. The occipital bone curves underneath to form the back and base of the skull. The foramen magnum is a large opening near the base of the occipital bone. This is where the vertebral column connects to the skull and the spinal cord enters the skull to communicate with the brain.

Several of the cranial and facial bones contain air spaces called sinuses, which make the skull lighter and give the human voice its characteristic tone and resonance. Each sinus is lined with tissue that secretes mucus, a thick, sticky fluid that helps trap particles in the air. The mucus then drains into the nasal cavity by small passageways.








The vertebral column is the main axis of the body (Johnson 2012). It supports the head, protects the spinal cord and serves as the site of attachment for the four limbs and various muscles.


The vertebrae are broken up into three sections that extend from the skull to the pelvis (Oellers online presentation 2012):



1.      The Cervical which contains seven vertebrae

2.      The Thoracic which contains twelve vertebrae

3.      The Lumbar which contains six vertebrae



Vertebrae share two points of contact called articulations located behind their main body. The vertebrae are separated from each other by flat, elastic, compressible intervertebral disk composed of a soft gelatinous center and a tough outer layer of fibrocartilage (Johnson 2012). Intervertebral disks act as shock absorbers, protecting the vertebrae from the impact of walking, jumping and other forms of movement.



A slipped disk or herniated disk happens when we make a sudden movement. This kind of movement forces the intervertebral disk outward, pressing against spinal nerves that result in intense back pain. If a disk ruptures, surgery can be performed to remove the damaged disk however; spinal flexibility will be decreased.


5.4a, 3 The ribs and sternum: Protecting the chest cavity






Humans have 12 ribs. One end of each rib branches from the chest cavity (thoracic region) and the other end attach to the sternum or breastbone by cartilage. The breastbone is a flat blade shaped bone composed of three separate bones that fuse together during development (Johnson 2012). The bottom two pairs of ribs are called floating ribs because they do not attach to the sternum at all.

The ribs, sternum and vertebral column form a protective rib cage that surrounds and protects the heart, lungs and other organs of the chest. The rib cage helps us breathe because the muscles between the ribs lift them slightly during breathing, expanding the chest cavity and inflating the lungs.



5.4b The appendicular skeleton: Pectoral girdle, pelvic girdle and limbs




http://disciplineorregret.com/?p=1998, Retrieved April 10, 2012.


The pectoral girdle, the pelvic girdle and the limbs make up the appendicular skeleton the second division of the human skeleton. These parts of the body are called appendages. The pectoral girdle consists of the shoulder, clavicle (collar bone) and scapulas (shoulder blade), the pelvic girdle consists of the hips (coxal bones), sacrum (pelvis) and pubic symphysis, limbs consist of femur (upper leg), tibia (lower leg, inside), fibula (lower leg, outside), ankle and foot bones.


5.4b, 1 The pectoral girdle lends flexibility to the upper limbs


The pectoral girdle is the supportive framework for the upper limbs, which consists of the right and left collarbones and the right and left shoulder blades.

The arms and hands consist of 30 different bones (Johnson 2012).

The upper end of the humerous (upper arm, the long bone) fits into the shoulder blade socket, while the other end of the humerus meets with the ulna (forearm, short bone, inside) and radius (forearm, long bone, outside).

The ulna and the radius are the two bones of the forearm at the elbow. When you hit your “funny bone” or elbow you actually struck the ulnar nerve that travels along the elbow.

The lower ends of the forearm bones meet the carpal bones (wrist bones), a group of eight bones that make up the wrist. The five metacarpal bones form the palm of the hand and they join with the 14 phalanges, which form the fingers and thumb (Johnson 2012).

The pectoral girdle and arms have a wide range of motion that provides the upper body a greater range of motion than any other joint in the body. The pectoral girdle and arms connect to the rest of the body by muscles and tendons that are attached loosely to provide a greater range of motion. However, the more flexibility you have the greater your chances are of falling because of instability. This can lead to fractured or broken bones. The collarbones are the most frequent broken bones in the body.


Having a wide range of motion allows us to easily excel in sports such as tennis, but repetitive motions such as swinging the tennis racket repeatedly can lead to health problems called repetitive stress syndromes. A well known repetitive stress syndrome is a condition of carpal tunnel syndrome a condition often due to repetitive typing (Johnson 2012).



5.4b, 2 The pelvic girdle supports the body


The pelvic girdle consists of the two coxal bones (hips) and the sacrum (pelvis) and coccyx (tailbone) of the vertebral column (the last four vertebrae that are fused together toward the pelvis). The pelvis is formed by the hip bones that attach to the sacral region of the vertebral column in the back, then curve forward to meet in front at the pubic symphysis, where they are joined by cartilage (Johnson 2012).

The primary function of the pelvic girdle is to support the weight of the upper body against the force of gravity and to protect the organs inside the pelvic cavity and serve as a site of attachment for the legs (Johnson 2012).

The lower limbs of the pelvic girdle have a less range of motion than the upper body of the pectoral girdle because the lower limbs are firmly connected to the rest of the body limiting dexterity.

The pelvic girdle is broader and shallower in women than men, mainly due to women being able to have a baby pass through the birth canal safely. The changes in the pelvic girdle becomes noticeable in women during puberty, when the women’s body begins to produce sex hormones that trigger a process of bone remodeling and shapes the female pelvic girdle to adapt for pregnancy and birth.

The femur (thighbone) is the longest and strongest bone in the body (Johnson 2012). The rounded upper end of each thighbone fits securely into a socket in a hipbone, creating a stable joint that supports the body, while moving. The lower end of the femur intersects at the knee joint with the larger of the two bones of the lower leg, the tibia (lower leg), which in turn makes contact with the thinner fibula (lower leg) (Johnson 2012). The patella (kneecap) is a triangle-shaped bone that protects and stabilizes the knee joint. At the ankle, the tibia and fibula join with the seven tarsal bones that make up the ankle and heel. Five long bones, the metatarsals, form the foot. The 14 bones of the toes, like those of the fingers, are called phalanges.


5.5  Joints form connections between bones

Joints, ligaments and tendons hold the skeleton together while allowing movement. Joints are called articulations; they are points of contact between bones. Ligaments and tendons are connective tissues that stabilize many joints.


5.5a  Joints vary from immovable to freely movable

Joints are classified by degree of movement into three classifications:



1.      Immovable

2.      Slightly movable

3.      Freely movable



There are three types of joints:



1.      Fibrous

2.      Cartilaginous

3.      Synovial



Fibrous joints are immovable. These immovable joints firmly connect the bones that protect and stabilize the skull and brain. At birth, fibrous joints are the flat bones in a baby’s skull that is separated by large spaces filled with fibrous connective tissue (soft spots). These soft spots or fontanels enable the baby’s head to change shape, so that it can squeeze safely through the mother’s pelvic opening during birth. As the baby matures, the fibrous joints harden and gradually become thin lines between skull bones.


Cartilaginous joints are slightly moveable allowing for some degree in motion. Cartilaginous joints connect the vertebrae in the backbone and those that attach the lower ribs to the sternum via hyaline cartilage.


Synovial joints are freely moveable in which the bones are separated by a thin fluid-filled cavity. The two bones of a synovial joint are fastened together and stabilized by ligaments. The interior of the cavity is lined with a synovial membrane, which secretes synovial fluid to lubricate and cushion the joint. To reduce friction the articulating surfaces of the two bones are covered with hyaline cartilage, a tough but smooth layer of cartilage. Together the synovial membrane and the surrounding hyaline cartilage constitute the joint capsule.


Different types of synovial joints permit different kinds of movements:



1.      Hinge joint (elbow/knee)

2.      Ball-and-Socket joint (shoulder and hip)



The hinge joint allows movement only in one direction.


The ball and socket joint permits movement in all directions such as in between the upper leg and hipbones and in between the upper arm and the pectoral girdle.

There are different types of movements made possible by hinge and ball-and-socket joints (Oellers, Online Presentation, 2012):




Retrieved April 10, 2012.



·         Abduction is the movement of a limb away from the body’s midline

·         Adduction is the movement of a limb toward the body’s midline

·         Rotation is movement around its own axis

·         Circumductions is movement of a limb that describes a cone

·         Flexion decreases the angle of a joint

·         Extension increases the angle of a joint

·         Hyperextension is the extension of a limb beyond its limit

·         Supination is the rotation of the forearm so that the palm faces forwards

·         Pronation is the rotation of the forearm so that the palm faces backwards



REFERENCES



            Johnson, M. D. (2012, 2010, 2008). Human Biology: concepts and current issues, sixth edition. Pearson Education, inc.; Benjamin Cummings.

            Oellers, J. (n.d). Online Presentation: Ch. 5 The Skeletal System. Retrieved April 10, 2012, from http://lblackboard.yc.edu/webapps/portal/frameset.jsp?tab_tab_group_id=_2_1&url=%2Fwebapps%2Fblackboard%2Fexecute%2Flauncher%3Dcourse%26id%3D_43466_1

                Science News (April 15, 2012). New Genetic Regions linked to Bone-weakening Diseases and Fractures. Retrieved April 10, 2012 from




Ch. 6 The Muscular System



Table of Contents



6.1 Muscles produce movement or generate tension

            a. The fundamental activity of muscle is contraction

            b. Skeletal muscles cause bones to move

            c. A muscle is composed of many muscle cells

            d. The contractile unit is a sarcomere

6.2 Individual muscle cells contract and relax

            a. Nerves activate skeletal muscles

            b. Activation releases calcium

            c. Calcium initiates the sliding filament mechanism

            d. When nerve activation ends, contraction ends

            e. Muscles require energy to contract and to relax

6.4 Cardiac and smooth muscles have special features

            a. How cardiac and smooth muscles are activated

            b. Speed and sustainability of contraction

            c. Arrangement of myosin and actin filaments



6.1 Muscles produce movement or generate tension



The body has three types of muscle (Johnson 2012):


Skeletal Muscle
           
Cardiac Muscle   


                       
 Smooth Muscle








1.      Skeletal

2.      Cardiac

3.      Smooth



The muscles main function is to produce movement or generate tension (Oellers, Online Presentation, 2012). The principle function of a muscle is to contract, which is the shortening distance between bones.



Skeletal muscle contraction is initiated by nerve activity only. Contraction requires energy that ultimately comes from stored carbohydrates or fats. Men consist of 40% skeletal muscle while women have 32% skeletal muscle (Johnson 2012). Skeletal muscles have many duties but a few examples are that skeletal muscles help control the focus of our eye and are responsible for us shivering when we are cold.



Some muscle movements are voluntary meaning we have control over their movement. Other muscle movement is involuntary for example your heart beat.



Muscles must generate heat in order to maintain homeostasis of our body temperature. Our body temperature is usually higher than our surroundings unless it is chili outside and then shivering occurs so that the muscles will contract and relax to generate heat.



6.1a The fundamental activity of muscle is contraction



The three types of muscle cells (skeletal, smooth and cardiac) have similar features such as (Johnson 2012):



·         Muscle cells contract in response to chemical or electrical signals from other organ systems

·         All muscles contract (shorten) and relax



6.1b Skeletal muscles cause bones to move



Skeletal muscles attach to the skeleton via tendons or attach to other muscles or to the skin and give us strength and mobility. A good example of skeletal muscles in action is allowing us to pick up tiny objects or any object.



The muscles are organized into pairs that are controlled by nerve activity only.



Muscle groups either work together which is called synergistic for example the pectorals and the triceps. These two muscles work together when doing a pushup, the triceps straightens the arm and the pectorals stabilize the upper body. Muscle groups that work against each other called antagonistic for instance, the forearm bends, when the biceps contracts and the triceps relax.



Each individual muscle produces a specific movement of one bone relative to another.







Skeletal muscles consist of an origin and insertion, which are the points of attachment to a muscle. The origin is the point of attachment of a muscle to the stationary bone, for example the scapula (Oellers, Online Presentation, 2012). The insertion is the point of attachment to the moveable bone, for example the biceps are attached via tendon to the insertion point and is attached to the radius across the joint (Oellers, Online Presentation, 2012). When a muscle contracts, the insertion is pulled toward the origin, which is closer to the midline of the body.



6.1c A muscle is composed of many muscle cells



A single or whole muscle is a group of individual muscle cells that all have the same origin and insertion with the same functions (Johnson 2012).






A muscle is arranged in bundles called fascicles each composed of many muscle cells and each surrounded by connective tissue (fascia). The fascia join together to become the tendon that attaches muscle to bone. Each fascicle contains a few dozen to 1000 of individual muscle cells or muscle fibers. Several layers of fascia cover the outer surface of the muscle. Individual muscle cells or muscle fibers are long and tube shaped (Oellers, Online Presentation, 2012). Each muscle contains more than one nucleus and contains myofibrils, which are long cylindrical structures arranged parallel and consume the entire interior of a cell (Johnson 2012). Myofibrils contain contractile proteins, actin and myosin (Oellers Online Presentation 2012).





 6.1d The contractile unit is a sacromere





Sacromeres is the contractile unit in a myofibril. Myofibril is composed of sacromeres joined end to end at the Z-line. Z-lines are attachment points for sacromeres (Oellers, online Presentation, 2012). Sacromeres contain thin filaments of actin that attach to the Z-lines and thicker filaments of myosin that span the gap between actin molecules.







6.2 Individual muscle cells contract and relax



During a muscle contraction, each sacromere shortens a little.



Contraction is what bridges the thick myosin and thin actin filaments (Oellers, Online Presentation, 2012).



Four things contribute to a skeletal muscle cell to contract and relax (Johnson 2012):



1.      Must be activated by a nerve

2.      Nerve activation increases calcium

3.      Calcium must be present for the muscles to contract

4.      When a muscle cell is no longer stimulated by a nerve, contraction ends



6.2a Nerves activate skeletal muscles



Motor neurons are nerves that stimulate skeletal muscle cells to contract. Motor neurons secrete a chemical called acetylcholine (ACH), which activates the cells to contract. The gap between the motor neurons and skeletal muscle cell is called the neuromuscular junction. For contraction to happen an electrical impulse must be able to bridge the gap. When an electrical impulse reaches the neuromuscular junction, acetylcholine releases. ACH then binds to receptor sites on the muscle cell membrane and is carried to the cell’s interior by T tubules. The function of the T tubules is to get the electrical impulse to all parts of the cell as quickly as possible (Johnson 2012). Myosin crosses over the bridge and draws the actin molecules closer together.



Science Daily April 11, 2012 wrote an article about a childhood disorder called spinal muscular atrophy (SMA) has been linked to an abnormally low level of a protein in certain nerve cells. SMA causes a child’s motor neurons to produce insufficient amounts of survival motor neuron protein (SMN). This causes the motor neurons to die leading to muscle weakness and the inability to move. There is no cure, but medicines and physical therapy help treat symptoms.





 





6.2b Activation releases calcium



The electrical impulse caused by the ACH (Acetylcholine) triggers the release of ionic calcium (Ca2+) from the sacroplasmic reticulum (SR), which stores the ionic calcium. The calcium then diffuses into the cells’ cytoplasm and the myosin-binding site is exposed. Myosin heads form cross-bridges with actin and the actin filaments are pulled toward the center of the sarcomere. Contraction then commences.





 6.2c Calcium initiates the sliding filament mechanism







Muscles contract when sarcomeres shorten and they shorten when the actin and myosin filaments slid past each other, known as the sliding filament mechanism of contraction (Johnson 2012). During contraction, the myosin (resembles a golf club) heads form a bridge with actin and then bend pulling the actin filaments toward the center of the sacromere.



In a relaxed state, nerve activation and contraction ends, the myosin heads do not make contact with actin. Calcium is pumped back into the sacroplasmic reticulum and calcium is also removed from the troponin therefore covering the myosin binding site. Muscles can relax because a protein molecule closely associated with the actin filaments called troponin and tropomyosin interfere with the myosin binding sites on the actin molecule in the absence of calcium. No calcium equals no cross-bridges, therefore contraction cannot happen.



When an electrical impulse happens, calcium is released from the sarcoplasmic reticulum and binds to troponin. This results in a shift of position, exposes the myosin binding sites, and permits the bridges pulling the actin filaments toward the center of the sacromere from each end.



6.2d When nerve activation ends, contraction ends



Relaxation of a muscle cell occurs when nerve activity ends.



ATP is required for contraction and relaxation (Oellers, Online Presentation, 2012).

ATP is needed to transport the calcium used for muscle contraction back to the SR for storage. As calcium decreases in the myofibril, the troponin-tropomyosin protein shifts back to its original position blocking the bridges to actin.



The interference of nerve cells can disrupt muscle function. Myasthenia gravis is a disorder which the body’s immune system attacks and destroys ACH receptors on the cell membrane of muscle cells. Resulting in muscles not being able to contract. This disorder can cause droopy eyelids and double vision.



6.2e Muscles require energy to contract and relax



Muscle contraction requires ATP. In the presence of calcium, myosin splits ATP into ADP releasing energy to do work. The energy is used to energize the myosin so that it can form a bridge to the actin. As long as calcium is present, the cycle of ATP breakdown repeats. The result is a shortening of the sacromere. After contraction, ATP is used to transport calcium back into the SR so that relaxation can occur. For relaxation to happen, an intact molecule of ATP must bind to myosin so that it can detach from actin. Muscle cells store only enough ATP for ten seconds worth (Johnson 2012).



 Once this energy is used up, cells must replenish ATP by (Oellers, Online Presentation, 2012):



·         Creatine Phosphate

·         Stored Glycogen

·         Aerobic Metabolism of Glucose, fatty acids and other high energy molecules



Creatine phosphate is a high-energy molecule with an attached phosphate group that transfers a phosphate group and energy to ADP and can create a new ATP molecule quickly. If ATP is not needed to power muscle contraction the excess ATP can be used to build a fresh supply of creatine phosphate, which is stored until needed. The combination of previous ATP plus stored creatine phosphate produces enough energy for thirty to forty seconds (Johnson 2012). Beyond that, muscles rely on stored glycogen (a complex sugar).



Glucose molecules are removed from glycogen and energy is used to create ATP. This breakdown of glucose happens without oxygen called anaerobic metabolism (Johnson 2012).



The most efficient long-term source of energy is the aerobic (takes place in the mitochondria and requires oxygen) metabolism of glucose in the blood, fatty acids derived from stored fat in fat cells and lactic acid (caused the burning sensation) (Johnson 2012).



After exercising, you continue to breathe heavily for a period of time. These deep breaths help reverse your body’s oxygen debt, because your muscles used more ATP early on than was provided by aerobic metabolism. The addition of ATP is provided by anaerobic metabolism with the buildup of lactic acid. The ability of muscle tissue to accumulate an oxygen debt and then repay it later allows muscles to perform at a near-maximal rate even before aerobic metabolism has increased (Johnson 2012).



Muscle fatigue is a decline in muscle performance during exercise caused by insufficient energy to meet metabolic demands due to depletion of ATP, creatine phosphate and glycogen stores within the muscle.



6.4 Cardiac and smooth muscles are activated



The cardiac muscle’s rhythmic contractions of the heart pump blood throughout the body. Smooth muscles in the walls of the uterus propel the child through the birth canal; they also push food through the digestive tract and transport urine from the kidneys to the bladder.





 6.4a How cardiac and smooth muscles are activated



Cardiac Muscle




Cardiac and smooth muscles are involuntary muscles. We have no control over them. They can contract without signals from the nerves, however; they both do respond to nerve activity. All cardiac muscle cells establish their own cycle of contraction and relaxation, those with the fastest rhythm are called pacemaker cells because they set the pace for the rest of the cells to follow. Cardiac muscle cells are joined at their blunt ends by intercalated discs; they contain gap junctions that permit one cell to electrically stimulate the next one.



Smooth muscle cells are joined by gap junctions, which permit the cells to activate each other so that the whole tissue contracts together. Cardiac and smooth muscle cells can contract without signals from the nervous system; however, they both respond to the nervous system. The effect of nerve activity may be either inhibitory or stimulatory. Changes in both inhibitory and stimulatory nerve activity to the heart are responsible for the increase in your heart rate when you exercise.



6.4 b Speed and sustainability of contraction



Skeletal muscle is the fastest muscle to contract, next is the cardiac muscle, which is moderately fast and then smooth muscle which contract very slow.



Cardiac muscles have contraction and relaxation cycle’s so the muscle will not fatigue.



Smooth muscles are partially contracted all the time. These muscles never fatigue because they contract so slowly that their ATP usage is always less than its procuring capability. Smooth muscles are the key player in the regulation of blood pressure (Johnson 2012).





 6.4c Arrangement of myosin and actin filaments


















http://www.britannica.com/EBchecked/media/46939/The-structure-of-striated-muscle-Striated-muscle-tissue-such-as, Retrieved April 9, 2012.

Cardiac muscle has thick and thin filaments arranged in sarcomeres called striated muscle (Johnson 2012).


The thick and thin filaments in smooth muscle are arranged in bundles that attach at various angles to the cell membrane. When these filaments slide past each other, the points of attachment are pulled toward each other and the cell gets shorter and fatter. Since the filaments are arranged in bundles other than sacromeres, the muscle is smooth in appearance other than having the striated look.



REFERENCES



            Johnson, M. D. (2012, 2010, 2008). Human Biology: concepts and current issues, sixth edition. Pearson Education, inc.; Benjamin Cummings.

            Oellers, J. (n.d). Online Presentation: Ch. 6 The Muscular System. Retrieved April 9, 2012, from http://lblackboard.yc.edu/webapps/portal/frameset.jsp?tab_tab_group_id=_2_1&url=%2Fwebapps%2Fblackboard%2Fexecute%2Flauncher%3Dcourse%26id%3D_43466_1

                Science News (April 11, 2012). Possible cause of movement defects in spinal muscular atrophy identification. Retrieved April 12, 2012 from http://www.sciencedaily.com/releases/2012/04/120411102723.htm




Ch. 7 Blood



Table of Contents



7.1 The components and functions of blood

            a. Plasma consists of water and dissolved solutes

            b. Red blood cells transport oxygen and carbon dioxide

            c. Hematocrit and hemoglobin reflect oxygen-carrying capacity

            d. All blood cells and platelets originate from stem cells

            e. RBCs have a short life span

            f. RBC production is regulated by a hormone

            g. White blood cells defend the body

                        1. Granular leukocytes: Neutrophils, eosinophils, and basophils

                        2. Agranular leukocytes: Monocytes and lymphocytes

            h. Platelets are essential for blood clotting

7.2 Hemostasis: Stopping blood loss

            a. Platelets stick together to seal a ruptured vessel

            b. A blood clot forms around the platelet plug

7.3 Human blood types

            a. ABO blood typing is based on A and B antigens

            b. Rh blood typing is based on Rh factor

            c. Blood typing and cross matching ensure blood capability



7.1 The components and functions of blood



The main human blood types are types A, B, AB and O. Blood type is determined by proteins called antigens on the surface of red blood cells. The circulatory system consists of the heart, the blood vessels and the blood that circulates through them (Johnson 2012). Blood is a connective tissue consisting of specialized cells and cell fragments suspended in a watery solution of molecules and ions (Johnson 2012).



There are three primary functions of blood (Oellers, Online Presentation, 2012):



1.      Transporting of nutrients, waste and hormones. Blood transports oxygen from the lungs, nutrients from the digestive system, and hormones from the endocrine glands and waste from body tissues to the organs for proper disposal.

2.      Regulation of body temperature, water volume in the body and pH of body fluids.

3.      Defense against infections and excessive bleeding by clotting.



These functions are crucial for maintaining homeostasis.



Components of blood fall into two major categories (Oellers Online Presentation 2012):



1.      Liquid Component: 55% Plasma (water, electrolytes, proteins, hormones, gases, nutrients and wastes.

2.      45% Cellular component or formed elements such as red blood cells, white blood cells and platelets.




7.1a Plasma consists of water and dissolved solutes



http://www.google.com/imgres?imgurl=https://ehealth.gov.mt/download.aspx%3Fid%3D1220&imgrefurl=https://ehealth.gov.mt/HealthPortal/health_institutions/Units/nbts/the_drop_journey/blood_journey_page.aspx&h=240&w=310&sz=71&tbnid=WdKKq-rdcnpK3M:&tbnh=92&tbnw=119&prev=/search%3Fq%3Dpicture%2Bof%2Bplasma%2Bin%2Ba%2Btest%2Btube%26tbm%3Disch%26tbo%3Du&zoom=1&q=picture+of+plasma+in+a+test+tube&docid=EzMRfdjZv0lk3M&hl=en&sa=X&ei=zDSKT_7uLYX28wSbsvXqCQ&ved=0CEAQ9QEwBg&dur=0, Retrieved April 8, 2012.


A blood sample that is being rotated to mimic gravity shows that the formed elements (red blood cells (RBCs), white blood cells (WBCs) and platelets) sink to the bottom of the test tube because they are denser than plasma which is the top layer and is a pale yellow color.


90% of plasma is water and the rest is dissolved proteins, hormones and other small molecules.


Plasma proteins are the large group of solutes in plasma that include albumins, globulins and clotting proteins.

Albumins is manufactured in the liver and maintains the water balance between blood and interstitial fluid while assisting some molecules and drugs in their transport in blood (Johnson 2012).

Globulin (alpha, beta and gamma) proteins transport various substances in the blood.


Beta globulins bind to lipid (fat) molecules creating a lipoprotein. Lipoproteins can be low-density lipoproteins (LDL) called the “bad cholesterol” that causes high blood pressure and increases the risk of cardiovascular disease and high-density lipoproteins (HDL). High levels of HDLs often indicate a lower risk of cardiovascular disease (Johnson 2012).


Gamma Globulins are part of the body’s defense system that aids in fighting off infections and illnesses.

Clotting proteins prevents the excessive loss of blood by blood clotting.


Plasma transports other molecules including ions (electrolytes), hormones, nutrients, waste products and gases.


Electrolytes (Na/Potassium) control cell functions and cell volume.

Hormones transport information throughout the body.

Nutrients are absorbed from the digestive tract or produced by cells’ metabolic reactions.

Waste produced in plasma includes:



·         carbon dioxide

·          urea

·         lactic acid.



Gases dissolved in plasma are oxygen, which is necessary for metabolism and carbon dioxide.


Waste is a product of metabolism.




7.1b Red blood cells transport oxygen and carbon dioxide




www.adam.com, retrieved April 8, 2012.



The main function of red blood cells (RBCs) is to carry oxygen and carbon dioxide. They are small, flattened, doughnut-shaped disks with thin concave centers and thick edges (Johnson 2012). Their structure helps RBC’s to be flexible allowing them to squeeze through tiny blood vessels. RBCs’ have no nucleus and contain no organelles. They are fluid-filling bags of plasma membrane and molecules of an oxygen-binding protein called hemoglobin (oxygen-carrying compound in RBCs), which consists of four polypeptide chains folded together each with a heme group containing a single iron atom. There are approximately 300 million of these molecules in every red blood cell. The iron atom forms bonds with oxygen molecules. A RBC can carry up to 1.2 billion molecules of oxygen.


Since RBCs lack mitochondria, they generate ATP by anaerobic (without oxygen) pathways.


Several factors influence the binding of hemoglobin to oxygen:



·         The concentration of oxygen must be high

·          The pH neutral. The lungs are a great place for this.



Oxygen is diffused into the blood plasma and then into RBCs, where it attaches to the iron atoms in the hemoglobin.




A picture of hemoglobin. The green, yellow, blue, and gray colors make up the four-polypeptide subunits of hemoglobin. Each subunit has its own heme group (shown in red.) The heme group is where the oxygen binds.

http://www.psc.edu/science/Ho/Ho.html, Retrieved April 8, 2012.


The hemoglobin binding to oxygen must be temporary so that oxygen is released to the cells that need it. In body tissue the concentration of dissolved oxygen and pH are low. Hemoglobin readily releases oxygen into body tissues. The increase in body heat increases the rate which hemoglobin releases oxygen.


Hemoglobin that has given up its oxygen is called deoxyhemoglobin and is a dark purple color. Hemoglobin also transports carbon dioxide (waste product of cellular metabolism).


7.1c Hematocrit and hemoglobin reflect oxygen-carrying capacity


Hematocrit is the percent of blood that consist of RBCs’. Normal hematocrit is 43 to 49 % for men and 37-43% for women (Johnson 2012). A low hematocrit may signal anemia (inadequate supply of hemoglobin in the RBCs) or other disorders of RBC production. A high hematocrit can signal polycythemia, a disorder of the bone marrow by an over production of RBCs.




7.1d All blood cells and platelets originate from stem cells





All blood cells and platelets originate from bones called stem cells that are constantly dividing in order to create immature blood cells (Johnson 2012). These blood cells develop into platelets and various types of mature red and white blood cells. Even stem cells from the pelvic bone may help hearts beat stronger. Science Daily (April 11, 2012) states in their article that researchers are using stem cells from pelvic bone marrow to restore tissue and improve heart function after muscle damage and heart attacks. By infusing certain stem cells into the area of the heart muscle that has been damaged from a heart attack, tissue can be preserved and heart function restored.



7.1e RBCs have a short life span







Some stem cells develop into immature cells called erythroblasts. They fill with hemoglobin and develop into mature RBCs within a week. They cannot reproduce because they have no nucleus or organelles and die out quickly.



RBCs originate from stem cells in bone marrow and have a short life span that is approximately 120 days (Oellers, Online Presentation, 2012). Within that time they make approximately 3000 round trips carrying oxygen from the lungs to the tissues and carbon dioxide from the tissues back to the lungs (Johnson 2012). Erythropoietin is a hormone that contains no nucleus and controls production of RBCs. To keep the hematocrit constant RBCs must be produced at a rate of more than 2 million per second (Johnson 2012).



Old and damaged RBCs are removed from the circulating blood and destroyed in the liver and spleen by large cells called macrophages by a process call phagocytosis. Macrophages are derived from monocytes the largest of the white blood cells (WBCs).



When the hemoglobin in RBCs are broken down in the liver, bilirubin mixes with bile and is secreted during digestion, which passes into the intestines. This pigment contributes to the colors of the urine and feces. Bilirubin is a yellowish pigment in the liver that the heme groups minus the iron are converted to during the breakdown of RBCs.



7.1f RBC production is regulated by a hormone



The hormone Erythropoietin regulates RBC production (Oellers, Online Presentation, 2012). The regulation of RBC production is a negative feedback control loop that maintains homeostasis. The number of RBCs are not regulated, just their ability to transport oxygen. The cells in the kidneys monitor the availability of oxygen (Oellers, Online Presentation, 2012). If the levels fall, the cells in the kidneys secrete erythropoietin, which is transported in the blood to the red bone marrow where it stimulates stem cells to produce more RBCs (Oellers, Online Presentation, 2012). People who suffer from a kidney disease do not produce enough erythropoietin to regulate RBC production properly. Erythropoietin is now available commercially for these individuals (Johnson 2012).



Blood doping is injecting erythropoietin (Johnson 2012). It is a practice used by some athletes to increase their blood-oxygen carrying capacity.



7.1g White blood cells defend the body



Approximately one percent of whole blood consists of white blood cells (WBCs) or leukocytes (Johnson 2012). WBCs are larger than RBCs. They contain a nucleus but no hemoglobin. There is one WBC for every 700 RBCs (Johnson 2012). WBCs originate from stem cells in the red bone marrow.



The function of WBCs is to protect from infection and regulate inflammatory reaction (Oellers, Online Presentation, 2012).



There are two categories of WBCs (Oellers, Online Presentation, 2012):



1.      Granular leukocytes (granulocytes)

2.      Agranular leukocytes (agranulocytes)



Both types contain granules (vesicles) in their cytoplasm that is filled with proteins and enzymes to assist in their defensive work.



WBCs have a short life span and many granular leukocytes die within a few hours to nine days due to injuries while fighting microorganisms. WBCs are constantly removed from the blood by the liver and spleen.



WBCs increase when viruses, bacteria, etc threaten the body. When activated by either tissue injury or microbes each type of WBC produces chemical that stimulates the production of new WBCs from the bone marrow.



7.1 g, 1 Granular leukocytes: Neutrophils, eosinophils, and basophils







Neutrophils are the first WBC to combat infection by engulfing foreign cells and are 60% of circulating WBCs (Oellers, Online Presentation, 2012).



Eosinophils are two to four percent of circulating WBCs and have two functions (Johnson 2012):



1.      Defend the body against large parasites, such as worms, by forming clusters of eosinophils that surround each parasite and bombard it with digestive enzymes.

2.      They also release chemicals that moderate the severity of allergic reactions.



Basophils is .5% of circulating WBCs (Oellers, Online Presentation, 2012). When body tissue are injured basophils secrete histamine (a chemical that initiates the inflammatory response) causing adjacent blood vessels to release blood plasma into the injured area. The plasma brings in nutrients, various cells, chemicals to begin tissue repair.



7.1g, 2 Agranular leukocytes: Monocytes and lymphocytes



Monocytes is five percent of the circulating WBCs (Oellers, Online Presentation, 2012). Monocytes are the largest WBC. They filter out the bloodstream and live in body tissues where they differentiate into macrophages (removes RBCs) and engulf invaders. They also stimulate lymphocytes to defend the body.




A picture of a Lymphocyte

http://en.wikipedia.org/wiki/Lymphocyte, Retrieved April 8, 2012.


Lymphocytes consist of thirty percent of circulation WBCs (Oellers, Online Presentation, 2012). Lymphocytes are found in the blood stream, tonsils, spleen, lymph nodes and thymus gland.

They can be classified into two types (Johnson 2012):





1.      B-lymphocytes (B cells) give rise to plasma cells that produce antibodies that defend against microorganisms and invaders.

2.      T lymphocytes (T cells) target and destroy bacteria, viruses and cancer cells.



7.1h Platelets are essential for blood clotting



Less than one percent of whole blood consist of platelets (Johnson 2012). Platelets are small cell fragments derived from megakaryocytic (large cells derived from stem cells in bone marrow) that play an important role in homeostasis (Oellers, Online Presentation, 2012).



Platelets are not living cells that last approximately five to nine days in the circulation (Johnson 2012). Platelets participate in blood clotting when a blood vessel is injured. During the repair process, platelets release proteins that promote blood vessel growth and repair.



7.2 Hemostasis: Stopping blood loss




A picture of the process of Hemostasis



Hemostasis is the natural process of stopping the excessive loss of blood.


Hemostasis has three stages (Oellers, Online Presentation, 2012):



1.      Vascular spasm or intense contraction of blood vessels to decrease blood flow.

2.      Platelet plug formation- the sealing of a ruptured blood vessel

3.      Coagulation or blood clotting


Once blood loss has stopped tissue repair can begin.



7.2a Vascular spasms constrict blood vessels to reduce blood flow



When a blood vessel is damaged, it contracts to decrease blood flow. Depending on the vessel size, can determine the reduction of blood flow speed. Small vessels contract and press the inner walls together and may stop the bleeding entirely.



7.2b Platelets stick together to seal a ruptured vessel



Platelets under normal conditions circulate freely; however, when a blood vessel is damaged platelets swell and develop spiky extensions. Platelets then begin to clump together resulting in a platelet plug that seals the injured area.



7.2c A blood clot forms around the platelet plug



The three stages in hemostasis (vascular spasm, platelet plug formation and blood clotting) is where the blood changes from a liquid to a gel creating a blood clot.



This involves a series of chemical reactions of three important clotting factors:



1.      Prothrombin activator

2.      Thrombin

3.      Fibrinogen



Prothrombin activator is released when there is damage to a blood vessel. This activates the conversion of prothrombin (a plasma protein) into an enzyme called thrombin. This requires calcium ions (Ca2+). Thrombin then facilitates the conversion of a soluble plasma protein fibrinogen into long insoluble threads of a protein called fibrin. The fibrin threads wind around the platelet plug that traps and holds platelet blood cells and various molecules against the opening. This results in an initial clot that decreases the flow of blood. Platelets in the clot start to contract, tightening the clot and pulling the vessel walls together. The blood clotting formation takes less than an hour to form (Johnson 2012).



A blood clotting disorder can be deadly. Hemophilia is a deficiency of one or more blood clotting factors (Johnson 2012). When a vessel is breached, blood clots slowly or not at all. This is due to factor VIII (a protein) missing (Johnson 2012).



7.3 Human blood types



Blood transfusion is putting foreign blood directly into the bloodstream of another person (Johnson 2012). Success depends largely on blood type, which is based on the ABO blood group system.



Blood typing deals with antigens (surface markers on RBCs) and antibodies (immune system protein, directed against antigens) (Oellers, Online Presentation, 2012).



Blood must be compatible when having a blood transfusion in order for our WBCs to not activate because of the blood not being compatible. The body recognizes these cells to be foreign cells that carry different surface proteins. The WBCs recognize these foreign cells as “nonself”.



An antigen is a nonself cell protein that stimulates the immune system. As part of the WBCs defense, the immune system produces an opposing protein called an antibody. Produced by lymphocytes antibodies belong to plasma proteins called gamma globulins (Johnson 2012). These antibodies attack the antigens, however; only a specific antibody can attack a specific antigen. Antibodies float freely in the blood and lymph until they encounter an invader with the matching antigen.



7.3a ABO blood typing is based on A and B antigens



RBCs are classified by the ABO blood group system.






There are four types:



1.      Type A

2.      Type B

3.      Type AB

4.      Type O



Type A blood has A antigens and makes B antibodies, type B blood has B antigens and makes A antibodies, type AB blood  make both A and B antigens and produces neither A or B antibodies and type O blood has neither A or B antigens and produces A and B antibodies.



All individuals have circulating antibodies that fight against surface antigens different from their own. Antibodies appear early in life and attack RBCs with foreign antigens, damaging them and causing them to clump together (agglutinate). This can result in blood vessels becoming blocked, organ damage or death if agglutination is extreme (Johnson 2012).



Any adverse effect of a blood transfusion is called a transfusion reaction (Johnson 2012). If you have type A blood you are restricted to receiving transfusions of type A or type O blood because neither of them has a foreign (type B) antigen and vice versa. People with type AB blood can receive transfusions from A, B, O, but not from other AB individuals. People with AB blood can donate only to other type AB people. Type O people can give blood to people of A, B or AB type, but they can receive blood only from Type O people. The antibodies of the recipient generally cause the transfusion reaction.



7.3b Rh blood typing is based on Rh factor


Rh factor is a RBC surface antigen that is important in blood transfusion. People either carry Rh on their RBCs or do not. People who are Rh-negative meaning they are not equipped with the Rh antigen, their immune system will respond to any foreign Rh antigen by making antibodies against it. Being Rh negative is a concern for pregnant women especially if they become pregnant by an Rh-positive man. If the fetus is Rh positive, its blood cells can leak into the mother’s blood and cause the mother to start producing anti-Rh antibodies. These antibodies can cross the placenta and attack the fetus’ RBCs. This can cause the fetus to have mental retardation or even death (Johnson 2012). To prevent this and Rh negative mother carrying an Rh positive child the mother is given an injection of anti-Rh antibodies at 28 weeks (Johnson 2012). This injection destroys any of the child’s RBCs that may have entered the mother’s circulation during childbirth, before her immune system has time to react.



Blood typing has several purposes. Here are a few (Johnson 2012):



·         Used in criminal investigations to compare the blood of victims and perpetrators

·         DNA tests to determine paternity



7.3c Blood typing and cross matching ensure blood compatibility



Blood typing involves determining your ABO type and the presence or absence of the Rh factor. For example, B positive means that you have type B blood and are positive for the Rh factor, (O-) means you have type O blood and negative for the Rh factor.


ABO blood typing is done by adding plasma containing small amounts of anit-A and anti-B antibodies to drops of diluted blood. If the blood agglutinates then it contains the antigens that match the antibodies. To ensure that blood transfusions are safe blood typing and cross matching is done.


Cross matching involves mixing small samples of donor blood with recipient plasma and recipient blood with donor plasma and examining both combinations for agglutination to be safe.





REFERENCES



            Johnson, M. D. (2012, 2010, 2008). Human Biology: concepts and current issues, sixth edition. Pearson Education, inc.; Benjamin Cummings.

            Oellers, J. (n.d). Online Presentation: Ch. 7 Blood. Retrieved April 8, 2012, from http://lblackboard.yc.edu/webapps/portal/frameset.jsp?tab_tab_group_id=_2_1&url=%2Fwebapps%2Fblackboard%2Fexecute%2Flauncher%3Dcourse%26id%3D_43466_1

                Science News (April 11, 2012). Stem cells from pelvic bone may preserve heart function. Retrieved April 12, 2012 from http://www.sciencedaily.com/releases/2012/04/120411102434.htm




Ch. 8 Heart and Blood Vessels



Table of Contents

8.1 Blood vessels transport blood

            a. Arteries transport blood away from the heart

            b. Arterioles and precapillary sphincters regulate

            c. Capillaries: Where blood exchanges substances with tissues

            d. Lymphatic system helps maintain blood volume

            e. Veins return blood to the heart

                        1. Skeletal muscles squeeze veins

                        2. One-way valves permit only one-way blood flow

                        3. Pressures associated with breathing push blood toward the heart

8.2 The heart pumps blood through the vessels

            a. The heart is mostly muscle

            b. The heart has four chambers and four valves

            c. The pulmonary circuit provides for gas exchange

            d. The systemic circuit serves the rest of the body



8.1 Blood vessels transport blood

The structure of blood vessels reflects their function. Thick-walled arteries and arterioles transport blood to the tissues under high pressure; capillaries allow fluid exchange between blood and interstitial fluid; large thin-walled veins store most of the blood and return it to the heart (Johnson 2012). High fat diets can damage our arteries reducing the amount of blood they transport to the heart. Science Daily (April 3, 2012) state that high fat diets cause damage to blood vessels and can cause high blood pressure. Researchers found that only after six weeks of high fat feeding to mice that their structural and mechanical properties of small arteries were rapidly altered. This can play a role in hypertension which puts a strain on the heart and can lead to cardiovascular heart disease.

The heart is a pump that is constructed entirely of living cells and cellular materials. The heart and blood vessels are known as the cardiovascular system. The heart provides the power to move the blood and the vascular system transports the blood to body parts. It is essential to maintaining homeostasis.

Blood vessels transports blood to all parts of the body.

1.        Blood rich in carbon dioxide is pumped from the heart into the lungs through the pulmonary arteries. (Arteries are blood vessels carrying blood away from the heart; veins are blood vessels carrying blood to the heart.)
2.        In the lungs, CO2 in the blood is exchanged for O2.
3.        The oxygen-rich blood is carried back to the heart through the pulmonary veins.
4.        This oxygen-rich blood is then pumped from the heart to the many tissues and organs of the body, through the systemic arteries.
5.        In the tissues, the arteries narrow to tiny capillaries. Here, O2 in the blood is exchanged for CO2.
6.        The capillaries widen into the systemic veins, which carry the carbon-dioxide-rich blood back to the heart.

http://www.chemistry.wustl.edu/~courses/genchem/Tutorials/Hemoglobin/effect.htm, Retrieved April 13, 2012.

Three types of Blood vessels transport blood (Oellers, Online Presentation, 2012):

1.      Arteries contain thick walls that carry blood away from the heart to body tissues under high pressure.

2.      Capillaries are microscopic and exchange solutes and water with cells of the body.

3.      Veins contain thin walls that store blood and return deoxygenated blood back to the heart.




8.1a Arteries transport blood away from the heart



Blood leaves the heart and enters the arteries where the blood is transported throughout the body.  Arteries have thick walls ranging from medium to large size enabling them to withstand the high pressure generated by the heart. Arteries resemble the roots of trees; they branch out and out and the further, they go the smaller in diameter the arteries become.

Arteries have the ability to stretch under pressure so that they can store the blood that is pumped into them with each beat of the heart and then provide it to the capillaries at high pressure. The elastic recoil of arteries maintains the blood pressure between heartbeats (Johnson 2012).



The structure of the artery vessel’s wall has three layers as follows: (Johnson 2012):







·         The thin innermost layer is the endothelium. This layer is flat and is the squamous epithelial cells. It is the continuation of the lining of the heart. The exterior of these cells are smooth due to the cells being compact. This keeps friction to a minimum and promotes smooth blood flow.



·         The second layer is composed of smooth muscle that is interwoven with elastic connective tissue. This is the thickest layer of most arteries. When this layer contracts because of the smooth muscle, the artery stiffens and helps resist the high pressure caused by the heart, but it does not construct the artery to alter blood flow. The elastic tissue interwoven into the smooth muscle allows the artery to stretch to accommodate the blood that enters with each heartbeat.



·         The outer layer is made of tough supportive connective tissue that consists primarily of collagen. This layer anchors vessels to surrounding tissues and helps protect them from injury.

Arteries can easily sustain injury because of the high pressure created by the beating of the heart. If the inner layer becomes damaged then blood can seep through the injured area and separate the outer layers causing an aneurysm. Aneurysms cause the smooth muscle and endothelial layer (inner layer) to bulge inward as they develop, narrowing the lumen or interior of the vessel to reduce blood flow to an organ or region of the body. Aneurysms can cause severe chest pain or they can be symptomless until they rupture causing massive internal bleeding that often results in death.

Aneurysms take years to develop and if detected can be repaired surgically. A stethoscope can detect them. Doctors use a stethoscope to listen to the flow of blood and can determine if an aneurysm has developed by this technique. A computerized tomography (CT) scan can also locate aneurysms before they rupture.



8.1b Arterioles and precapillary sphincters regulate blood flow



Arterioles are the smallest arteries about the width of a piece of thread. By the time blood flows through the arterioles, blood pressure has fallen considerable. Arterioles generally lack the outer most layer of connective tissue and their smooth muscle layer is not as thick.

Arterioles store and transport blood as well as help regulate the amount of blood that flows to each capillary. They accomplish this by contracting or relaxing the smooth muscle layer, altering the diameter of the arteriole lumen.

Where an arteriole joins a capillary there are bands of smooth muscles called precapillary sphincter. They serve as gates that control blood flow into individual capillaries.

Vasodilatation increases blood flow to capillaries, while vasoconstriction (contraction of vascular smooth muscle) and precapillary sphincters reduce arterioles diameter so reducing blood flow to the capillaries (Oellers, Online Presentation, 2012).

Nerves, hormones and conditions in the local environment of the arterioles and precapillary sphincters can produce a wide variety of external and internal factors of the vasoconstriction (Johnson 2012). For example, your fingers will become pale if you go outside on a day when it is freezing. This happens because the vasoconstriction produced by the nerves is narrowing your vessel reducing heat loss from your body. Vice versa on a hot day, your skin will appear flushed because the vasodilatation occurs to speed up heat loss and cool you off.



8.1c Capillaries: Where blood exchanges substances with tissues



Arterioles connect to the smallest blood vessels called the capillaries.

Capillaries consist of thin walls that allow red blood cells to pass through.

Networks of capillaries are called capillary beds and can be found in all regions of the body causing you to bleed no matter where you are cut.

The design of capillaries and their thin, porous walls allow blood to exchange oxygen, carbon dioxide, nutrients, and waste products with tissue cells (Johnson 2012). Capillary walls consist of a single layer of squamous epithelial cells. Pores pierce this layer and the cells are separated by narrow slits. The slits are large enough to allow the exchange of fluid and other materials between blood and the fluid that surrounds every living cell (interstitial fluid), yet small enough to retain red blood cells and most plasma proteins.

Capillaries function as biological strains that permit selective exchange of substances with the fluid surrounding the cell. Capillaries are the only blood vessels that can exchange materials with the interstitial fluid.



8.1d Lymphatic System helps maintain blood volume

There is an imbalance between the amount of plasma fluid filtered by the capillaries and the amount reabsorbed. This excess plasma fluid must be returned to the cardiovascular system or all the plasma will end up in the interstitial fluid (Johnson 2012).



The lymphatic capillaries, which are a system of blind-ended vessels that branch throughout our body tissues, pick up the excess plasma fluid.

The lymphatic system also picks up objects in the interstitial fluid that are too large to diffuse into the capillaries which include lipid droplets absorbed during digestion and invading organisms.

The lymphatic capillaries transport the excess plasma fluid and large objects to larger lymphatic vessels that will return the fluid to the veins near the heart.

This is how the lymphatic system maintains the proper volumes of blood and interstitial fluid.


8.1e Veins return blood to the heart


From the capillaries, blood flows back to the heart through venules (small veins) and veins.

Veins have three layers of tissue like arteries. Unlike arteries, veins consist of much thinner walls of the outer two layers than arteries. Veins also have a larger diameter lumen as well.

Veins have thinner walls compared to arteries because there is not as much pressure build up from the heart beating. As blood moves through the cardiovascular system the blood pressure becomes lower and lower so by the time the blood reaches the veins the pressure has decreased by a lot. The large diameter of the veins allows them to stretch so that they can accommodate large volumes of blood.

Veins serve as a blood volume reservoir for the entire cardiovascular system. This is approximately two-thirds of all the blood in your body (Johnson 2012). This reservoir of blood allows your heart to continue beating when your body is dehydrated keeping your blood pressure constant (Johnson 2012).


A picture of varicose veins


If veins become dilated this can lead to varicose veins which are permanently swollen veins that look bumpy from the pool of blood. Veins become varicose when the leaflets of the valves no longer meet properly and the valves do not work (Oellers, Online Presentation 2012). This allows the blood to flow backwards and the veins enlarge. They are most common in the feet and legs. Varicose veins can be treated by injecting a solution that shrivels the vessels and makes them less visible. This will not affect the blood flow because the undamaged adjacent veins will take over and return blood to the heart.


Many parts assist the vein in returning blood to the heart (Oellers, Online Presentation, 2012):

1)      Contractions of skeletal muscles

2)      One-way valves inside the veins

3)      Pressure changes associated with breathing



8.1e, 1 Skeletal muscles squeeze veins

Skeletal muscles squeeze veins collapsing them and pushing blood back to the heart. Moving around instead of standing still improves the return of blood to your heart and prevents fluid buildup in your legs, which cause varicose veins.

8.1e, 2 One-way valves permit blood flow

One-way valves permit blood flow only one way toward the heart. They open to permit blood to move toward the heart and then close whenever the blood begins to flow backwards. Together skeletal muscles and valves form the skeletal muscle pump (Johnson 2012). Once blood has been pushed toward the heart by skeletal muscles the blood cannot drain in the direction of gravity because of these one-way valves. The opening and closing of these valves depend on the difference in blood pressure on either side of the valve.

8.1e, 3 Pressures associated with breathing push blood toward the heart

Changes in the chest (thoracic) and abdominal cavities create a pressure change that aids in pushing blood toward the heart (Johnson 2012). When we inhale, abdominal pressure increases and squeezes abdominal veins. At the same time pressure within the thoracic cavity decreases dilating thoracic veins. The result of these to actions create pressure that pushes the blood toward the heart. This is sometimes called the respiratory pump.


8.2 The heart pumps blood through the vessels


A picture of a human heart

http://www.picsearch.com/imageDetail.cgi?id=it9kiI6jHR5F0-G07gHNbV2xA90oKGHyt20facz4pAY&width=1663&start=1&q=picture of a human heart, Retrieved April 13, 2012.

Your heart is slightly larger than your fist and is cone shaped (Johnson 2012). The heart is located in the chest cavity between the lungs and behind the sternum or breastbone. The heart consists mostly of cardiac muscle that pumps ceaselessly in a squeezing motion to propel blood through the blood vessels. The heart pumps about 75 times every minute not including the increase in heart rate (Johnson 2012). Under normal circumstances the heart’s rate of pumping is controlled by the brain, but can also beat on its own without any instructions from the brain.

8.2a The heart is mostly muscle

The heart is surrounded in a tough fibrous sac called the pericardium, which protects the heart, anchors it to surrounding structures and prevents it from overfilling with blood (Oellers, Online Presentation 2012). The pericardial cavity separates the pericardium from the heart. This cavity contains a film of lubricating fluid that reduces friction and allows the heart and the pericardium to glide smoothly against each other when the heart contracts (Johnson 2012).

The walls of the heart consist of three layer (Oellers, Online Presentation 2012):

·         The epicardium is the thin layer of the epithelial and connective tissue

·         Myocardium is the thick layer of cardiac muscle that contracts every time the heart beats squeezing the chambers inside the heart and pushing blood outward into the arteries.

·          Endocardium is the thin layer of the endothelial tissue that rests on a layer of connective tissure.

Factors that can lead to inflammation in or around the heart wall is infections, cancer, injuries or complications from major surgery. Antibiotic and anti-inflammatory drugs work well to combat against inflammation.

8.2b The heart has 4 chambers and four valves



The heart consists of four separate chambers (Oellers, Online Presentation):

·         Two at the top are called the atria.

·          The two at the bottom are more muscular and called the ventricles.



The septum is a muscular partition that separates the right and left sides of the heart.

Blood returning to the heart from the body’s tissues enters the heart at the right atrium and passes through a valve into the right ventricle.

The right ventricle is more muscular than the right atrium because it pumps blood at pressure through a second valve and into the artery leading to the lungs.

Blood returning from the lungs to the heart enters the left atrium and then passes through a third valve into the left ventricle. The muscular left ventricle pumps blood through a fourth valve into the body’s largest artery the aorta. From the aorta, blood travels through the arteries and arterioles to the capillaries, venules and veins and then back to the right atrium again (Johnson 2012).

The left ventricle is more muscular than any of the heart’s four chambers because this ventricle must generate pressures higher than the aortic blood pressure to pump blood into the aorta.

The right ventricle has thinner walls because the blood pressure in the arteries leading to the lungs is about one-sixth that of the aorta.

Four heart valves enforce the heart’s one-way flow pattern and prevents blood from flowing backwards. The right and left atrioventricular valves (AV) located between the atria and their adjacent ventricle prevents blood from flowing back into the atria when the ventricle contract. The AV valves consist of thin connective tissue flaps that project into the ventricles. These valves are supported by strands of connective tissues called the chordae tendineae that connect to muscular extensions of the ventricle walls called papillary muscles (Johnson 2012). Together these connective tissues prevent the valves from opening backwards into the atria when the ventricle contract.

Two semilunar valves (the pulmonary and the aortic) prevent backflow into the ventricle from the main arteries leaving the heart when the heart relaxes (Johnson 2012). Each semilunar valve consists of three flaps.

8.2c The pulmonary circuit provides for gas exchange

The heart pumps blood through the lungs (the pulmonary circuit) and throughout the rest of the body to all the cells (the systemic circuit) simultaneously. Each circuit has its own set of blood vessels.

The pulmonary circuit (Johnson 2012):

           












When deoxygenated (Oxygen has been given to tissue cells and taken up carbon dioxide) blood returns to the heart from the veins it enters the right atrium.

1.      From the right atrium, blood passes through the right atrioventricular valve into the right ventricle.

2.      The right ventricle pumps blood through the pulmonary semilunar valve into the pulmonary trunk (the main pulmonary artery) leading to the lungs. The pulmonary trunk divides into the right and left pulmonary arteries which supply the right and left lungs.

3.      At the pulmonary capillaries, blood gives up carbon dioxide and receives a fresh supply of oxygen from the air we inhale.

4.      The freshly oxygenated blood flows into the pulmonary veins leading back to the heart. It enters the left atrium and flows through the left atrioventricular valve into the left ventricle.

The deoxygenated blood in the right side of the heart never mixes with oxygenated blood in the left. Deoxygenated blood leaving the right side of the heart must pass through the pulmonary circuit (where it picks up oxygen) before it reaches the left side of the heart.

Purpose of the Circulatory System (Oellers, Online Presentation 2012):

The Circulatory System distributes

·         Heat

·         Water

·         Immune System related cells

·         Carbon Dioxide

·         Nutrients

·         Waste

8.2d The systemic circuit serves the rest of the body




When blood enters the left ventricle, it begins the systemic circuit, which takes it to the rest of the body

The process of the systemic circuit (Oellers, Online Presentation, 2012):



1.      The oxygenated blood travels from the left ventricle through the aortic semilunar valve to the aorta.

2.      Through the branching arteries and arterioles to the tissues.

3.      Through the arterioles to capillaries.

4.      From Capillaries into venules and veins.

5.      To the vena cana and into the right atrium.

The heart requires a great deal of oxygen and nutrients to fuel its own operations so the heart has its own set of blood vessels called the coronary arteries. These arteries branch from the aorta just above the aortic semilunar valve and encircle the heart’s surface. From there they send branches inward to supply the myocardium. Cardiac veins collect the blood from the capillaries in the heart muscle and channel it back to the right atrium. The coronary arteries are small in diameter if they become blocked serious health issues can result.



REFERENCES



            Johnson, M. D. (2012, 2010, 2008). Human Biology: concepts and current issues, sixth edition. Pearson Education, inc.; Benjamin Cummings.

            Oellers, J. (n.d). Online Presentation: Ch. 8 Heart and blood vessels. Retrieved April 13, 2012, from http://lblackboard.yc.edu/webapps/portal/frameset.jsp?tab_tab_group_id=_2_1&url=%2Fwebapps%2Fblackboard%2Fexecute%2Flauncher%3Dcourse%26id%3D_43466_1

                Science News (April 3, 2012).Arteries under pressure early on: mice fed a high-fat diet show signs of artery damage after only 6 weeks. Retrieved April 12, 2012 from http://www.sciencedaily.com/releases/2012/04/120411102434.htm





Chapter 9 The Immune System and Mechanisms of Defense



Table of Contents



9.1 Pathogens cause disease

            a. Bacteria: Single-celled living organisms

            b. Viruses: Tiny infectious agents

            c. Prions: Infectious proteins

            d. Transmissibility, mode of transmission, and virulence determine health risk

9.2 The lymphatic system defends the body

            a. Lymphatic vessels transport lymph

            b. Lymph nodes cleanse the lymph

            c. The spleen cleans the blood

            d. Thymus gland hormones cause T lymphocytes to mature

            e. Tonsils protect the throat

9.3 Keeping pathogens out: The first line of defense

            a. Skin: An effective deterrent

            b. Impeding pathogen entry in areas not covered by skin

                        1. Tears, saliva, and earwax

                        2. Mucus

                        3. Digestive and vaginal acids

                        4. Vomiting, urination, and defecation

                        5. Resident bacteria

9.4 Nonspecific defenses: The second line of defense

            a. Phagocytes’ engulf foreign cells

            b. Inflammation: Redness, warmth, swelling, and pain

            c. Natural killer cells target tumors and virus-infected cells

            d. The complement system assists other defense mechanisms

            e. Interferon’s interfere with viral reproduction

            f. Fever raises body temperature

9.5 Specific defense mechanisms: The third line of defense

            a. The immune system targets antigens

            b. Lymphocytes are central to specific defenses

            c. B cells: Antibody-mediated immunity

            d. The five classes of antibodies

            e. Antibodies’ structure enables them to bind to specific antigens

            f. T cells: Cell-mediated immunity

                        1. Helper T cells stimulate other immune cells

                        2. Memory T cells reactivate during later exposures

9.6 Immune memory creates immunity

9.7 Medical assistance in the war against pathogens

            a. Active immunization: An effective weapon against pathogens

            b. Passive immunization can help against existing or anticipated infections

            c. Monoclonal antibodies: Laboratory-created for commercial use

            d. Antibiotics combat bacteria

9.9 Inappropriate immune system activity causes problems

            a. Allergies: A hypersensitive immune system

            b. Autoimmune disorders: Defective recognition of “self”

                        1. Lupus erythematosus: Inflamed connective tissue

                        2. Rheumatoid arthritis: Inflamed synovial membranes





9.1 Pathogens cause disease



All around us are bacteria, viruses and prions. Most are harmless and beneficial, but the ones that cause disease are pathogens. They come from outside the body to cause us harm. Our immune system and other general defense mechanisms work to protect us against pathogens (Johnson 2012): The skin, stomach acid, tears and actions such as vomiting and defecation are ways of expelling or neutralizing pathogens before they can harm us.


A picture of Nonspecific defense mechanisms





Nonspecific defense mechanisms help the body respond to generalized tissue damage and the common bacteria and some viruses, Specific defense mechanisms enable the body to recognize and kill specific bacteria and other foreign cells and to neutralize viruses.



All three mechanisms work together to protect us from pathogens. The immune system is made up of cells, proteins, and structures of the lymphatic and circulatory system; it is only capable of killing or neutralizing pathogens or abnormal cells it recognizes.



Pathogens include bacteria, viruses, fungi and a few protozoa and possibly prions (Johnson 2012).



9.1a Bacteria: Single-celled living organisms







Bacteria are single-celled organisms that do not have a nucleus or membrane-bound organelles (Johnson 2012). Bacteria can take on the shape of a sphere, rod or spiral because their outer surface is covered by a rigid cell wall. Bacteria is smaller than a human cell giving it an advantage. They contain a higher surface-to-volume ratio making it easier to obtain raw materials and getting rid of wastes by diffusion. Necessary to maintain life, grow and divide. Bacteria uses ATP and amino acids for making proteins the same as a human cell. Bacteria can obtain raw materials anywhere. Some bacteria break down raw sewage and cause the decomposition of dead animals and plants (Johnson 2012). Others can obtain nutrients from the soil and air (Johnson 2012). Through the use of bacteria antibiotics, hormones, vaccines and genetic engineered foods have been produced. Some bacteria are pathogens that rely on living human cells for their energy supply and in the process they damage or kill the human cells. They can cause pneumonia, tonsillitis, tuberculosis, botulism, toxic shock syndrome, syphilis, Lyme disease and many other diseases (Johnson 2012). Bacterial infections can be treated with antibiotics that inhibit or abolish the growth of bacteria, fungi and protozoa.



9.1b Viruses: Tiny infectious agents










http://www.mc3cb.com/viruses.html, Retrieved April 8, 2012.



Viruses are smaller much smaller than bacteria and consist of either RNA or DNA surrounded by a protein coat (Johnson 2012). Viruses use their DNA or RNA to force a living cell to make more copies of the virus. They have no organelles so they cannot grow or reproduce. Viruses are dead or alive it is an ongoing debate; however, they cannot reproduce until they take over a living cell. The virus uses the cell’s organelles to reproduce.



Viruses can enter a living cell by entering the cell’s cytoplasm by endocytosis (transporting the virus into a cell by using a coated vesicle). Once inside the cell the protein coats are dissolved and the viral genetic material is released for incorporation into the cells’ genetic material (Johnson 2012). Other viruses merge their outer coat with the cell membrane and release their genetic contents into the cell’s cytoplasm and other viruses attach to the outer surface of the cell membrane and inject the genetic material into the cell (Johnson 2012). The presence of the viral genetic material causes the cell to begin producing thousands of copies of the virus. Viral infections can vary in degrees of seriousness depending on a persons’ health and age. Antibiotics generally do not work against viral infections.



9.1c Prions: Infectious proteins




A picture of a normal prion on the left and a disease-causing prion on the right.




Prions are normal brain proteins that are not folded correctly (Oellers, Online Presentation, 2012). Prions destroy nerve cells in the brain and spinal cord by triggering nearby normal forms of the protein to misfold as well, causing your body to experience bizarre behaviors. Eventually so many prions accumulate within infected brain cells that the cells die and burst, releasing prions to infect other brain cells and causing the death of nerve cells.



There is no known cure for prion infection. They resist freezing, drying, and cooking (Oellers, Online Presentation 2012). Infection occurs when humans eat cattle that have been infected with mad cows’ disease causing a human disease called variant Creutzfeldt-Jakob disease (vCJD) (Johnson 2012).



9.1 d Transmissibility, mode of transmission, and virulence determine health risk



Factors that determine the danger of a pathogen include (Johnson 2012):



·         How easily it is passed from one person to another (mucus to hand, cold)

·         How it is transmitted (exchange of bodily fluid, food, blood, air)

·         How damaging the resulting disease is (cold minor, Aids deadly)



9.2 The lymphatic system defends the body



The lymphatic system performs three important functions (Johnson 2012):



·         Helps maintain the volume of blood in the cardiovascular system (by returning excess fluid back to the capillaries and back to the cardiovascular system)

·         Transports fats and fat-soluble vitamins absorbed from the digestive system to t he cardiovascular system

·         Defends the body against infection





Most of the cells of the immune system live in the lymphatic system. The basic components consist of the network of lymph vessels throughout the body, the lymph nodes, the spleen, the thymus gland, and the tonsils and adenoids (Johnson 2012).



9.23a Lymphatic vessels transport lymph



The lymphatic system begins as a network of small, blind ended lymphatic capillaries in the vicinity of the cells and blood capillaries (Johnson 2012). They contain wide spaces between overlapping cells allowing them to absorb substances that are too large to enter a blood capillary like bacteria.



The fluid in the lymphatic capillaries is called lymph a milky body fluid that contains WBCs, proteins, fats and can contain bacteria and viruses. The lymphatic capillaries merge to form the lymphatic vessels that consist of three thin layers. The lymphatic vessels merge to form larger vessels creating two major lymphatic ducts : the right lymphatic duct and thoracic duct (Johnson 2012).The two lymph ducts join the subclavian veins in the shoulders and returning the lymph to the cardiovascular system.



9.2b Lymph nodes cleanse the lymph



Lymph nodes remove microorganisms, cellular debris and abnormal cells from the lymph before returning it to the cardiovascular system (Johnson 2012). Lymph nodes are located at intervals along the lymphatic vessels. There are hundreds of them and can be found in the digestive tract, neck, armpits and groin (Johnson 2012).






Inside the lymph nodes is connective tissue and two types of WBC, macrophages and lymphocytes that identify microorganisms and remove them.



The lymphatic vessels carry lymph into and out of each node in one direction by the used of one-way valves. As the fluid flows through a node, the macrophages destroy foreign cells by phagocytosis and the lymphocytes activate other defense mechanisms (Johnson 2012). The clean lymph fluid flows out of the node and continues to the veins.



9.2c The spleen cleanses blood



The spleen is the largest lymphatic organ. It is soft, fist sized mass located in the upper-left abdominal cavity (Johnson 2012).



The organ is filled with two types of tissue (Johnson 2012):



1.      Red pulp contains macrophages that scavenge and break down microorganisms and damaged RBCs and platelets. Clean blood is stored here.

2.      White pulp contains lymphocytes that search for foreign pathogens.



The spleen has two main functions (Johnson 2012):



1.      Controls the quality of circulating red blood cells, by removing the old and damaged ones.

2.      Helps fight infection.



Infections such as leukemia can enlarge the spleen and can cause it to rupture causing internal bleeding. Surgery is necessary to remove the spleen. We can live without a spleen because our lymph glands, liver and red bone marrow aid in circulating RBCs, removing them and fighting infection.



9.2d Thymus gland hormones cause T lymphocytes to mature



The thymus gland plays a key role in the body’s immune response. Science Daily (March 29, 2012) state in their article, that researchers have generated artificially thymus tissue in a mouse embryo to enable the maturation of immune cells.



The thymus gland facilitates maturation of T lymphocytes (Oellers, Online Presentation, 2012).



The thymus gland secretes two hormones (Johnson 2012):



1.      Thymosin

2.      Thymopoietin



These two hormones cause lymphocytes called T (cells) to mature and take on specific defenses. The thymus gland varies in size according to age. It is largest and most active during childhood. As we age our thymus gland stops growing and begins to shrink and can eventually disappear to be replaced by fibrous and fatty tissue. The thymus gland is found in the lower neck, behind the sternum and just above the heart (Johnson 2012).



9.2e Tonsils protect the throat



Lymphocytes in the tonsils gather and filter out many microorganisms that enter the throat in food and air (Johnson 2012). Tonsils are lymphatic tissue located near the entrance of the throat and along with adenoids they protect the throat (Oellers, Online Presentation, 2012).



Adenoids are lymphatic tissue that if continued to enlarge obstruct airflow from nose to throat causing mouth breathing, a nasal voice and snoring. Adenoids usually disappear by puberty, but can continue to grow and cause problems.



9.3 Keeping pathogens out: The first line of defense



Our bodies have several ways to prevent pathogens from entering into our bodies: Our skin, tears, saliva, earwax, mucus, to name some of the few.







9.3a Skin: An effective deterrent



The skin is the most important barrier to keep pathogens out.



The skin has four key attributes that make it an effective barrier (Johnson 2012):



1.      Structure. The outer most layer of our skin is called keratin (fingernails are made of). Keratin forms a tough elastic barrier keeping microorganisms at bay.

2.      Constantly being replaced meaning that any pathogens deposited on the surface of the skin are shed along with the dead cells.

3.      Acidic pH because of sweat glands producing sweat.

4.      Production of an antibiotic by sweat glands called dermicidin kills harmful bacteria.



9.3b Impeding pathogen entry in areas not covered by skin



Pathogens are most effective when entering our bodies through moist surfaces such as mucous membranes that line the digestive, urinary, respiratory and reproductive tracts along with the eyes and ears.



These moist areas have defenses to block pathogens from entering into our bodies such as tears, saliva, earwax, mucus, vomiting, urination and defecation to name the few.




9.3b, 1 Tears, saliva and earwax



Tears lubricate the eyes while washing away particles. Tears and saliva contain lysozyme, which is an enzyme that kills many bacteria (Johnson 2012). Saliva lubricates the tissues inside of the mouth and rinses microorganisms from the mouth into the stomach where stomach acid destroys them. Earwax traps small particles and microorganisms.



9.3b, 2 Mucus



Mucus is sticky and secreted by cells like the lining of the digestive tract and the airways of the respiratory system. Mucous binds microorganisms to itself so that it cannot enter our bodies. Our bodies get rid of the mucous by cilia (hair like projections) in our airways that sweep the mucus toward our throat where we cough or swallow the mucus containing the microorganism (Johnson 2012).



9.3b, 3 Digestive and vaginal acids



Vaginal secretions are slightly acidic, but not anything like a digestive tract that is undiluted. It strong enough to kill nearly all pathogens that enter on an empty stomach. Bacteria called Helicobacter pylori that have evolved to endure the stomach acid cause a stomach ulcer.



9.3b, 4 Vomiting, urination, and defecation



Vomiting is a way for the body to get rid of toxin or microorganisms.



The urinary system is slightly acidic and constantly flushing of urination keeps bacteria low.



Defecation helps remove microorganisms from the digestive tract. Diarrhea is caused by an illness where the muscles in the intestinal wall start to contract rapidly and the intestines secrete additional fluid into the feces (Johnson 2012).



9.3b, 5 Resident bacteria



Beneficial bacterial often reside in the mucous membranes lining the vagina and the digestive tract. They help control population levels of harmful organisms by competing for food and winning. They also lower the vagina pH levels where many fungi and bacteria cannot survive.





9.4 Nonspecific defenses: The second line of defense







Nonspecific defense mechanisms include the immune system cells that engulf and digest foreign cells, chemicals that are toxic to foreign cells, proteins that interfere with viral reproduction, and the development of a fever (Johnson 2012).



Our second line of defense do not target specific pathogens but respond to all.



Nonspecific defenses include phagocytes, natural killer cells, the inflammatory response, the complement system, interferon’s’ and fever.



9.4a Phagocytes engulf foreign cells





Phagocytes are white blood cells that surround and engulf invading bacteria (Oellers, Online Presentation 2012). This is a process known as phagocytosis (Johnson 2012). Phagocytosis begins when the phagocyte captures the bacterium, surrounds it and encloses the bacterium in a membrane-bound vesicle. Inside the cell, the vesicle fuses with lysosomes, which dissolve the bacterial membranes, and the wastes and debris are discarded.



Neurtophils and macrophages and eosinophils are types of phagocytes.



Neutrophils are the first white blood cells to respond to infection (Johnson 2012). They digest and destroy bacteria and some foreign fungi in the blood and tissue fluids.



Monocytes are white blood cells that leave the vascular system enter the tissue fluids and develop into macrophages. Macrophages engulf and digest large numbers of foreign cells including viruses and bacterial parasites. Macrophages also scavenge old blood cells, dead tissue fragments and cellular debris as a tool for cleanup (Johnson 2012). Macrophages create new white blood cells by releasing a chemical that stimulates production of white blood cells.



Eosinophils engulf and digest invaders that are too big for the other phagocytes. They accomplish this by bombarding large parasites with digestive enzymes.



White blood cells increase when the body is fighting infection. Tissue fluid, dead phagocytes and microorganisms and cellular debris accumulate at the infection sited producing pus. An abscess forms when pus becomes trapped and the body forms skin over the infected areas. Common places for abscesses are the breast (mastitis, the gums (dental abscesses) and the liver or brain. You can drain an abscess or some require that you take antibiotic drugs or surgical removal to get rid of an abscess.



9.4b Inflammation: Redness, warmth, swelling and pain







Inflammation has four outward signs (Johnson 2012):



1.      Redness

2.      Warmth

3.      Swelling

4.      Pain



These events prevent damage from spreading, dispose of cellular debris and pathogens and aid in tissue repair mechanisms.



When tissue is damaged the inflammatory process begins. Chemicals bare released from the damaged cells; this begins the process. These chemicals stimulate mast cells which are connective tissue cells specialized to release histamine. Histamine promotes dilation of neighboring blood vessels.



White blood cells are too big to cross capillary walls. Histamine makes it possible for WBCs to squeeze through the walls into the interstitial fluid where they attack foreign organisms and damaged cells. The dilation of blood vessels brings more blood into the injured area making it red and warm. The rising temperature increases phagocyte activity. Swelling is caused by the capillary walls allowing more fluid to seep into the tissue spaces. This extra fluid dilutes pathogens and toxins and brings in clotting proteins that form a fibrin mesh to wall off the damaged areas from healthy tissue (Johnson 2012). The extra fluid also carries in extra oxygen and nutrients to promote in the healing of tissue and carries away dead cells, microorganisms and other debris from the area.



Pain forces the injured person to rest to aid in the healing process. Pain is caused by the swollen tissue pressing against nerve endings.



9.4c Natural killer cells target tumors and virus-infected cells



Natural killer (NK) cells are a type of lymphocytes (white blood cells) that attacks tumor cells and viruses (infected cells) (Oellers, Online Presentation, 2012). NK cells are not phagocytes; instead, they release chemicals that break down their targets’ cell membranes. They are able to recognize certain changes that take place in the plasma membranes of tumor cells and virus-infected cells. The target of a NK cells destroys the cell’s nucleus and the target cell’s membranes develop holes. The NK cells aid in the inflammatory response by secreting substances.



9.4d The complement system assists other defense mechanisms





The complement system is made up of approximately 20 plasma proteins that assist other defense mechanisms by circulating in the blood (Johnson 2012). Once activated the protein than activates another protein and so on creating a domino effect. Some activated proteins can join to form large protein complexes that create holes in bacterial cell walls causing them to swell and burst. Other activated complement proteins bind to bacterial cell membranes, marking them for destruction by phagocytes. Others stimulate mast cells to release histamine or serve as chemical attractants to draw additional phagocytes to the infection.



9.4e Interferons interfere with viral reproduction



Viruses cannot reproduce on their own; they must invade a host’s cell in order to reproduce.



Cells that become infected by viruses secrete a group of proteins call interferons (Johnson 2012). Interferons diffuse to nearby healthy cells and bind to their cell membranes. They then stimulate the healthy cells to produce proteins that interfere with the reproduction of viral proteins making it harder for viruses to infect the protected cell.



Interferon proteins can protect against viral diseases such as genital warts, hepatitis B and one form of leukemia (Johnson 2012).



9.4f Fever raises body temperature



A normal body temperature is 98.6 F. When macrophages detect and attract bacteria, viruses, or other foreign substances, they release certain chemicals into the bloodstream called pyrogens (Johnson 2012). Pyrogens cause the brain to raise your body temperature. Modest fevers help the body to fight infection by increasing the metabolic rate of body cells, speeding up both defense  mechanisms and tissue-repair processes. When the infection is gone macrophages stop releasing pyrogens and your body temperature returns to normal. Abnormally high fevers can be dangerous in adults. If your core temperature reaches 105 F your brain begins to fry; seek medical attention.



9.5 Specific defense mechanisms: The third line of defense



Specific defense mechanisms involve the production of antibodies and T cells that recognize and inactivate one specific pathogen. Specific defense mechanisms have a memory component that remembers initial exposure and responds more quickly and aggressively on subsequent exposures (Oellers, Online Presentation 2012).



The immune system is made up of cells, proteins and the lymphatic system that work together to detect and kill particular pathogens and abnormal body cells.





9.5a The immune system target antigens







An antigen is any substance that triggers an immune response (Oellers, Online Presentation, 2012). The immune system responds to each uniquely shaped antigen by producing specific antibodies to attack and inactivate the antigen.



All antigens are located on the outer surface of a cell or virus. Human cells have unique proteins on the surfaces that our immune system uses to recognize that the cells belong to us. These are self-markers known as major histocompatibility complex (MHC) proteins. Each person has a unique set of MHC proteins that would act as antigens in another person’s body.



9.5b Lymphocytes are central to specific defenses



Lymphocytes are white blood cells that synthesize from stem cells in bone marrow. Found in the bloodstream, tonsils, spleen, lymph nodes and thymus gland they total about 30% of circulating WBCs (Johnson 2012).





There are two types of lymphocytes (Johnson 2012):







1.      B cells

2.      T cells



B cells mature in bone marrow and are responsible for antibody-mediated immunity. In other words, they produce antibodies (proteins that bind with and neutralize specific antigens). B cells protect us best from viruses, bacteria and foreign molecules that are soluble in blood and lymph, because B cells release antibodies into the lymph, bloodstream and tissue fluid.



T cells mature in the thymus gland and are responsible for cell-mediated immunity. T cells directly attack foreign cells, coordinate the immune response from other cells, are active against parasites, fungi, viruses, intercellular bacteria, cancer cells, and cells with “non-self” MHC (Oellers, Online Presentation, 2012).





9.5c B cells: Antibody-mediated immunity



As B cells mature, they develop unique surface receptors that allow them to recognize specific antigens. When a B cell encounters a surface antigen with the matching receptor, it activates the B cell’s surface receptors and bind to the antigen. The B cell begins to grow and multiply producing more B cells exactly like the original with the same surface receptors called clones.



Some of the clone cells become memory cells that lie in wait for the next exposure to the antigen and other clone cells become plasma cells. Plasma cells secrete antibodies into the lymph fluid and ultimately into the blood plasma.



9.5d The five classes of antibodies



Antibodies belong to the class of blood plasma proteins called gamma globulins also known as immunoglobulin (Ig) (Johnson 2012).



There are five classes of Ig:







1.      IgG are the most prevalent in blood. They are found in blood, lymph, intestines and tissue fluid. They activate the complement system and neutralize any toxins. They are the only antibodies that cross the placenta during pregnancy and pass on the mother’s acquired immunities to the fetus.

2.      IgM are the antibodies that are the first to be released during immune responses. Found in blood and lymph, they activate the complement system and cause foreign cells to clot.

3.      IgA are antibodies that enter areas of the body covered by mucous membranes, such as the digestive, reproductive, and respiratory tracts. There they neutralize pathogens. They are also present in mother’s milk and are transmitted to the infant during breast-feeding.

4.      IgD are antibodies in the blood, lymph, and B cells. Their function is not clear.

5.      IgE  are the rarest of the antibodies. They are in B cells, mast cells and basophils. They activate the inflammatory response by triggering the release of histamine. They also trigger allergic responses.





9.5e Antibodies’ structure enables them to bind to specific antigens



The immune system produces the antibody that is an exact match to an antigen that allows the antibody to neutralize the antigen.



All antibodies share the same basic structure that consist of four linked polypeptide chains arranged in a Y shape. Each of the four chains has a constant region that forms the trunk and two branches and a variable region that represents the antigen-binding site (Johnson 2012). Each variable region has a unique shape that fits only one specific antigen.          

                                                                                               

                                                                                                                                    








http://homepage.usask.ca/~kmj127/Immuno.html, Retrieved April 8, 2012.



9.5f T cells: Cell-mediated immunity



There are two basic functional differences between B cells and T cells (Johnson 2012):



1.      B cells produce circulating antibodies

2.      T cells either release chemicals that stimulate other cells of the immune system or they directly attack the foreign cell and kill it.



T cells originate from stem cells in bone marrow and mature in the thymus (Oellers, Online Presentation, 2012).



Macrophages and activated B cells act as antigen-presenting cells (APCs) that engulf foreign particles, then lysosomes partially digest the pathogen. A vesicle containing MHC molecules binds to the digestive vesicle and a fragment of the antigen form an antigen MHC complex that is displayed on the surface of the cell when the vesicle fuses with the cell membrane and releases its digestive products. T cells recognize fragments of the antigen along with its own cell-surface self marker.



T cells develop two sets of surface proteins once they mature (Oellers, Online Presentatino, 2012):





1.      CD4 T cells are memory and helper cells

2.      CD8 T cells will become cytotoxic and suppressor cells



These proteins determine what type of T cell they will become.



9.5f, 1  Helper T cells stimulate other immune cells



CD4 becomes a helper T cell when its receptors encounter an antigen-presenting cell displaying a fragment of an antigen. This new T cell undergoes mitosis producing a clone which recognizes the same antigen. Most of the cells in the helper T cell clone will secrete cytokines, which stimulate other immune cells such as phagocytes, natural killer cells, and T cells with CD8 receptors.



Helper T cells are crucial to an effective immune response. Without them the immune response would be nonexistent. AIDS is so devastating because HIV destroys helper T cells, weakening the body’s ability to mount a cell-mediated immune response (Johnson 2012).



Cytotoxic T cells are the only T cells that directly attack and destroy other cells. Cytotoxic T cells are produced when a mature T cell with CD8 receptors meets an antigen-producing cell that displays an antigen fragment.

When a cytotoxic T cell is activated it locates and binds to a target cell, secretary vesicles release a protein called perforin into the space between the two cells (Johnson 2012). The perforin molecules assemble themselves into a pore in the target cell, allowing water and salts to enter. This will eventually kill the cell. The cytotoix T cell also releases granzyme, a toxic enzyme that is small enough to pass through the pore (Johnson 2012). Then it detaches from the target cell and goes off in search of other prey.



9.5f, 2 Memory T cells reactivate during later exposures



Memory cells are reactivated when an antigen that originally stimulated their production is presented to them again. Memory T cells are an important factor that distinguishes specific defenses from nonspecific defense mechanisms.



9.6  Immune memory creates immunity



Your first exposure to a particular antigen generates a primary immune response. This involves recognition of the antigen and production of B and T cells. The primary immune response takes three to six days after the antigen first appears to start synthesizing specific B cells. Antibodies reach their peak about 10-12 days after first exposure (Johnson 2012).



B and T cells create memory cells this is the basis for immunity from disease. Secondary immune response kicks in when the initial antigen pops up again. This time however within hours after the exposure to the same antigen memory cells bind to the pathogen. Within a few days antibodies respond.



Why can a person get a cold or flu over and over again? The reason being is that the cold and flu are viruses that evolve rapidly changing every year. Their antigens change enough that each one requires a different antibody and each exposure triggers a primary response.



9.7 Medical assistance in the war against pathogens



Through medicine, we have been able to produce medicines and vaccines to help us combat pathogens. Immunizations help the body resist specific pathogens.



9.7a Active immunization: An effective weapon against pathogens



Vaccines are a strategy for causing the body to develop immunity to a specific pathogen (Oellers, Online Presentation, 2012). This way when we are introduced to the pathogen again our secondary immune response will activate shielding us from the danger of the disease.



The process of activating the body’s immune system in advance is called active immunization (Johnson 2012). There are issues of safety, time and expense when it comes to vaccines.  First, vaccines are produced from dead or weakened pathogens for example the polio vaccine made from weakened poliovirus. Vaccines that are made from live, but weakened pathogens make better vaccines because they eject a greater immune response; however, this type of vaccine can cause the disease itself. Second, a vaccine confers immunity against only one pathogen, so a different vaccine is needed for every virus. Third, vaccines do not cure an existing disease.



Active immunizations produce long-lived immunity that can protect us for many years. The widespread practice of vaccinations has greatly reduced many diseases such as polio, measles and whooping cough (Johnson 2012).



9.7b Passive immunization can help against existing or anticipated infections



Passive immunization is administering protective antibodies to an individual (Oellers, Online Presentation, 2012). This type of immunization produces short-term protection because the administered antibodies disappear from the circulation quickly because the person’s own B cells aren’t activated and so memory cells for the pathogen do not develop.



Passive immunizations has been used effectively against common viral infections like hepatitis B and measles.





9.7c Monoclonal antibodies: Laboratory-created for commercial use







Monoclonal antibodies are produced in the laboratory from cloned descendants of a single hybrid B cell (Johnson 2012). They are antibodies that are made specific for a single antigen.



Monoclonal antibodies are synthesized by immunizing a mouse with a specific antigen. Then extracting the B cells from the mouse’s spleen and fusing antibody-producing B cells with cancer (myeloma) cells to produce fast-growing cells. The desired antibody is the separated out and cloned producing millions of copies. This is why monoclonal antibodies are proving useful in research, testing and cancer treatments because they are pure and they can be produce cheaply in large quantities.



Monoclonal antibodies are used in home pregnancy tests, screening for prostate cancer and diagnostic testing for hepatitis, influenza and HIV/AIDS (Johnson 2012).



9.7d Antibiotics combat bacteria



Antibiotic means against life (Johnson 2012). Antibiotics kill bacteria or stop their growth. The difference between bacteria and human cells is that bacteria have a thick cell wall and human cells do not. Bacterial DNA is not safely enclosed in a nucleus, human DNA is, and bacterial ribosome’s are smaller than human ribosome’s. Bacterial rate of protein synthesis is very rapid and they grow and divide. Antibiotics are ineffective against viruses they can only combat against bacteria. Most antibiotics kill bacteria by interfering with bacterial protein synthesis or bacterial cell wall synthesis.



9.9 Inappropriate immune system activity causes problems



Inappropriate immune system activity can lead to allergies and autoimmune diseases such as lupus erythematosus and rheumatoid arthritis.




9.9a Allergies: A hypersensitive immune system



10% of North Americans suffer from allergies (Johnson 2012). Allergies are hypersensitivity reactions (Oellers, Online Presentation 2012).



An allergy is an inappropriate response of the immune system to an allergen. An allergen is any substance (antigen) that causes an allergic reaction (not a pathogen, but the body reacts, as though it is a pathogen) (Oellers, Online Presentation, 2012). Exposure to an allergen triggers a primary immune response, causing B cells to produce specific IgE (allergic reactions fall into this group) antibodies. The IgE antibodies bind to mast cells (found in connective tissue) and to circulating basophiles.







When the same allergen enters the body a second time, it binds to the IgE, antibodies on mast cells and basophiles, causing them to release histamine. The result is an allergic reaction, a typical inflammatory response that includes warmth, redness, swelling, and pain in the area of contact with the allergen (Johnson 2012).



Some allergens affect only the areas exposed others include food allergens and bee sting venom are absorbed or injected into the bloodstream. Such allergens elicit a systemic response meaning they affect several organ systems. Systemic responses include constriction of smooth muscle in the lungs making it difficult to breathe and digestive system and dilation of blood vessels (Johnson 2012).



When the circulatory collapses with a life threatening fall in blood pressure this is known as anaphylactic shock (Johnson 2012). People with this condition should be rushed to the hospital because the reaction can be fatal. People who know that they have allergic reactions such as to bee stings are advised to carry an emergency kit with them that contains a self-injected hypodermic needle of epinephrine, a hormone that dilates the airway and constricts peripheral blood vessels, preventing shock.



9.9b Autoimmune disorders: Defective recognition of “self”



The immune system’s on occasion can fail to distinguish self from nonself. When this happens the immune system produces antibodies and cytotoxic T cell that target its own cells (Johnson 2012). Autoimmune disorders are conditions that result from this happening. At the moment there are no cures for autoimmune disorders. Treatments include therapies that depress the body’s defense mechanisms and relieve the symptoms. Autoimmune conditions include multiple sclerosis, a progressive disorder of the central nervous system, Type 1 diabetes mellitus, which targets cell in the pancreas, lupus erythematosus and rheumatoid arthritis.



9.9b, 1 Lupus erythematosus: Inflamed connective tissue



Lupus is an autoimmune disorder in which the body attacks its own connective tissue (Johnson 2012). One type of lupus called discoid lupus erythematosus primarily affects areas of the skin exposed to sunlight. Systemic lupus erythematosus affects the heart, blood vessels, lungs, kidneys, joints and brain. Lupus often starts as a red skin rash on the face or head and can include fever, fatigue, joint pain and weight loss. Spreading inflammation can lead to osteoarthritis, pericarditis or pleurisy (inflammation of the lining of the lungs). Medications can reduce the inflammation and alleviate the symptoms.



9.9b, 2 Rheumatoid arthritis: Inflamed synovial membranes



Rheumatoid arthritis is a type of arthritis involving inflammation of the synovial membrane that lines certain joints (Johnson 2012). At first, fingers, wrists, toes or other joints become painful and still. Over time the inflammation destroys joint cartilage and the neighboring bone. Eventually bony tissue begins to break down and fuse resulting in deformities and reduced range of motion. The disease is intermittent, but with each recurrence the damage is progressively worse. Pain-relieving medications can help, as can regular mild exercise and physical therapy to improve range of motion.





REFERENCES



            Johnson, M. D. (2012, 2010, 2008). Human Biology: concepts and current issues, sixth edition. Pearson Education, inc.; Benjamin Cummings.

            Oellers, J. (n.d). Online Presentation: Ch. 9 The immune system and mechanisms of defense. Retrieved April 8, 2012, from http://lblackboard.yc.edu/webapps/portal/frameset.jsp?tab_tab_group_id=_2_1&url=%2Fwebapps%2Fblackboard%2Fexecute%2Flauncher%3Dcourse%26id%3D_43466_1

                Science News (March 29, 2012).Artificial thymus tissue enables maturation of immune cells. Retrieved April 12, 2012 from http://www.sciencedaily.com/releases/2012/04/120411102434.htm









Ch. 10 The Respiratory System: Exchange of Gases



Table of Contents



10.1 Respiration takes place throughout the body

10.2 The respiratory system consists of upper and lower respiratory tracts

            a. The upper respiratory tract filters, warms, and humidifies air

            b. The lower respiratory tract exchanges gases

                        1. The larynx produces sound

                        2. Bronchi branch into the lungs

                        3. The lungs are organs of gas exchange

                        4. Gas exchange occurs in alveoli

                        5. Pulmonary capillaries bring blood and air into close contact

10.3 The Process of breathing involves a pressure gradient

            a. Inspiration brings in air, expiration expels it

            b. Lung volumes and vital capacity measure lung function

10.4 Gas exchange and transport occur passively

            a. Gases diffuse according to their partial pressures

            b. External respiration: The exchange of gases between air and blood

            c. Internal respiration: The exchange of gases with tissue fluids

            d. Hemoglobin transports most oxygen molecules

            e. Most Carbon Dioxide is transported in plasma as bicarbonate

10.5 The nervous system regulates breathing

            a. A respiratory center establishes rhythm of breathing

            b. Chemical receptors monitor carbon dioxide, hydrogen and oxygen levels

            c. We can exert some conscious control

10.6 Disorders of the respiratory system

            a. Reduced airflow or gas exchange impedes respiratory function

                        1. Asthma: Spasmodic contraction of bronchi

                        2. Emphysema: Alveoli become permanently impaired

                        3. Bronchitis: Inflammation of the bronchi

                        4. Cystic fibrosis: An inherited condition

            b. Microorganisms can cause respiratory disorders

                        1. Colds and the flu: Common viral respiratory tract infections

                        2. Pneumonia: Infection inflames the lungs

                        3. Tuberculosis: Bacterial infection scars the lungs

                        4. Botulism: Poisoning by bacterial toxin

            c. Lung cancer is caused by proliferation of abnormal cells

            d. Pneumothorax and atalectasis: A failure of gas exchange

            e. Congestive heart failure impairs lung function





10.1 Respiration takes place throughout the body



The function of the respiratory system is to exchange these gases (oxygen and carbon dioxide) with the air (Johnson 2012). We extract oxygen from the air we breathe and exhale carbon dioxide, the waste product of our metabolism. The oxygen in the air comes from the plants. The plants absorb carbon dioxide through their leaves and use it to accomplish photosynthesis (turning carbon dioxide into oxygen).



Respiration includes four processes (Oellers, Online Presentation, 2012):



1.      Breathing (ventilation) is the movement of air into and out of the lungs and uses associated bones, muscles and nerves to accomplish this.

2.      External respiration is the exchange of gases between inhaled air and blood that takes place in the lungs.

3.      Internal respiration is the exchange of gases between the blood and tissue fluids.

4.      Cellular respiration is the process of using oxygen to produce ATP within cells. Cellular respiration generates carbon dioxide as a waste product.



The respiratory system is also responsible for the production of sound (vocalization).



10.2 The respiratory system consists of upper and lower respiratory tracts







The respiratory system is divided into the upper and lower respiratory tracts.



The upper respiratory tract includes (Oellers, Online Presentation, 2012):



·         The nose (passageway for air) and nasal cavity (filters, warms and moistens air)

·         Pharynx (throat) is the common passageway for air, food and liquid. The pharynx is located above the “Adam’s apple” in your neck.



The lower respiratory tract includes (Oellers, Online Presentation 2012):



·         Larynx (voice box) is used for the production of sound.

·         Trachea (windpipe) is the main airway.

·         Bronchi are branching airways that stem from the trachea.

·         Lungs is the organ of gas exchange.



10.2a The upper respiratory tract filters, warms, and humidifies air



The nose is not just used as a passageway for air, but has many purposes (Johnson 2012):



·         Contains receptors for the sense of smell

·         Filters inhaled air and screens out some foreign particles.

·         Moistens and warms incoming air.

·         Provides a resonating chamber that helps give your voice its characteristic tone



The outer portion of the nose is called the external nose, while the internal area of the nose is known as the nasal cavity. The outer area of the nose is made up of cartilage in the front and two nasal bones behind the cartilage.



The external nose and nasal cavity are divided into two chambers by the nasal septum (Johnson 2012). Air enters through the nostrils and is filtered partially by the nose hairs. The air then flows into the nasal cavity, which is lined with moist epithelial tissue that is supplied with blood vessels. These blood vessels help to warm incoming air and the epithelial tissue secretes mucus, which humidifies the air (Johnson 2012). Cilia are tiny hair like projections that cover the epithelial tissue.



Mucus in the nasal cavity trap dust, pathogens and other particles in the air, before they enter further into the respiratory tract. The cilia move the mucus toward the back of the nasal cavity and pharynx by creating gentle movement back and forth. There the mucus is coughed out or swallowed where it is digested by stomach acid. In cold weather, your nose is likely to run because the cilia in the nasal cavity slow down and allows mucus to pool in the nasal cavity and drip from the nostrils.



Sinuses are the air spaces inside the skull lined with tissue that secretes mucus to help trap foreign particles. The sinuses drain into the nasal cavity by small passageways. Two tear ducts that carry fluid away from the eyes, drain into the nasal cavity as well. Excessive tears will also makes your nose “runny” because of the passageways from the sinuses to the nasal cavity.



Incoming air enters the pharynx (throat) next. The pharynx connects the mouth and nasal cavity to the larynx (voice box) (Johnson 2012). The upper pharynx extends from the nasal cavity to the roof of the mouth. Into it, open the two auditory tubes (Eustachian tubes) that drain the middle ear cavities and equalize air pressure between the middle ear and outside air (Johnson 2012). The lower pharynx is a common passageway for both food and air. Food passes through the pharynx to the esophagus, and air flows through to the lower respiratory tract.



10.2b The lower respiratory tract exchanges gases



The lower respiratory tract includes (Johnson 2012):



·         Larynx

·         Trachea

·         Bronchi

·         Lungs with bronchioles and alveoli



10.2 b, 1 The larynx produces sound



The larynx or voice box extends two inches below the throat.



The voice boxes purpose is to (Johnson 2012):



·         Maintain an open airway.

·         Route food and air into the appropriate channels

·         Assist in the production of sound.














http://www.mybwmc.org/library/2/1118, Retrieved April 14, 2012.



The voice box contains the epiglottis, a flap of cartilage located at the opening to the voice box. When air flows, through the pharynx the epiglottis is open, but when we swallow food or liquids the epiglottis blocks the opening, resulting in food and beverages into the esophagus and digestive system than into the trachea.













http://www.woering.nl/pg_veterinair.html, Retrieved April 14, 2012.



The vocal cords consist of two folds of connective tissue that extend across the airway (Johnson 2012). The glottis is surrounded by vocal cords and is the opening to the airway. Ligaments support the vocal cords.



The skeletal muscles control how tightly the vocal cords are stretched which produces the unique sounds of our voices. The vibration of the vocal cords makes the sound. When we are not talking, our vocal cords are relaxed and open, but when we start to talk they stretch tightly across the tracheal opening, and the flow of air past the vocal cords cause them to vibrate (Johnson 2012).



The volume of pitch we have in our voices is contributed to the tension on our vocal cords. High-pitched tones are from cords that are short and stretched tightly and vice versa with deep pitched voices. Testosterone in men contributes to them having a deep voice. In puberty, testosterone causes the larynx to enlarge at puberty adjusting the tension on their vocal cords.



The mouth, throat, nose and nasal cavity, tongue and teeth also determine our distinct voices (Johnson 2012). Muscles in the throat, tongue, soft palate, and lips create sounds. The throat, nose and nasal sinuses serve as resonating chambers to amplify tones.





10.2 b, 2 The trachea transports air







The trachea is the windpipe that extends from the larynx to the left and right bronchi. The trachea transports air to and from the lungs (Oellers, Online Presentation 2012). The trachea consists of smooth muscle and layers of epithelial and connective tissue held open by tough, flexible C-shaped bands of cartilage (Johnson 2012).



The C-shaped bands keep the trachea open at all times and permit the trachea to change diameter when we cough or breathe heavily due to the bands being an incomplete circle.



The trachea is lined with cilia covered epithelial tissue that secretes mucus.



Choking occurs when a foreign object is lodged in the trachea. If the airway is completely blocked death can occur. Choking stimulates receptors in the throat that trigger the cough reflex. This is a sudden expulsion of air from the lungs in an attempt to dislodge foreign object (Johnson 2012).



10.2, b 3 Bronchi branch into the lungs







The trachea branches into two airways called the right and left bronchi as it enters the lung cavity. Bronchioles are small airways that lack cartilage. The walls of bronchi contain fibrous connective tissue and smooth muscle reinforced with cartilage. As the airways get smaller and smaller the cartilage decreases.



The bronchi and bronchioles have many functions: (Johnson 2012)



·         Transport air.

·         Clean the air.

·         Warm the air to body temperature.

·         Saturate air with water vapor before it reaches the lungs.



Smoking is terrible on the respiratory tract. It irritates it, destroys the cilia allowing mucus and debris from the smoke to accumulate in the airway, resulting in “Smoker’s cough”. Coughing is the body’s way to dislodge a foreign object or mucus in this case from the airway. Accumulation of mucus leads to frequent infections because pathogens and irritants remain in the respiratory tract (Johnson 2012).



10.2b, 4 The lungs are organs of gas exchange







The lungs consist of supportive tissue that encloses the bronchi, bronchioles, blood vessels and the areas where gas exchange occurs (Johnson 2012). The heart is what separates the right lung from the left. Each lung is enclosed in two layers of thin epithelial membranes called the pleural membranes. One layer represents the outer lung surface and the other layer contains a small amount of watery fluid that reduces friction between the pleural membranes as the lungs and chest wall move during breathing. Pleurisy is the inflammation of the pleural membranes resulting in a decrease in the secretion of pleural fluid, increase friction and cause pain during breathing (Johnson 2012). The lungs consist of several lobes that can be surgically removed without eliminating lung function. The right lungs consist of three lobes and the left lung two. Each lobe contains a branching tree of bronchioles and blood vessels.





10.2b, 5 Gas exchange occurs in alveoli







Lungs are very soft and mostly consist of air. The lungs are a system of branching airways that end in 300 million tiny air-filled sacs called alveoli (Johnson 2012). Alveoli is  where the gas exchange takes place. A single alveolus is a thin bubble of living squamous epithelial cells only one cell layer thick. Within each alveolus, certain epithelial cells secrete a lipoprotein called surfactant that coats the interior of the alveoli and reduces surface tension that is caused by the attraction of water molecules toward each other. Without surface tension, the alveoli could collapse.




10.2b, 6 Pulmonary capillaries bring blood and air into close contact







Gas exchange occurs between the alveoli and pulmonary capillaries. The right ventricle of the heart pumps deoxygenated blood into the pulmonary trunk, which splits into the left and right pulmonary arteries. These arteries become smaller and turn into arterioles, eventually terminating in a capillary bed called the pulmonary capillaries. Only the squamous epithelial cell of the alveolus and the cell of the capillary wall separate blood from air (Johnson 2012). Veins then collect the oxygenated blood from the pulmonary capillaries and return the blood to the left side of the heart where it is transported to all parts of the body. Heart attacks occur when the blood vessels going to the heart become filled up with plaque and the heart is not getting enough oxygen to fulfill its duties. More than 30% of the one million heart attack victims in the U.S. each year die before seeking medical attention. Science Daily (April 13, 2012) writes in their article that researchers are studying the benefits of the AngelMed Guardian and implantable medical device. This device is currently undergoing clinical trials that alert users about potential heart attacks through a combination of vibrations, audible tones and visual warnings.



10.3 The process of breathing involves a pressure gradient



Breathing consists of getting air into and out of the lungs; this requires muscular effort. Since the lungs do not contain skeletal muscle tissue, the surrounding bones and muscles expand when the lungs expand resulting in the expansion of the chest cavity. These bones and muscles consist of the ribs, the intercostals muscles between the ribs and the main muscle of respiration the diaphragm (a skeletal muscle that separates the chest from the abdominal cavity).



10.3a Inspiration brings in air, expiration expels it



Air moves into and out of the lungs in a cyclic manner.



Below is the general principle of gas pressure and how these gases move (Johnson 2012):



·         Colliding molecules of gas cause gas pressure.

·         When the volume of a closed space increases, the molecules of gas in that space are farther away from each other, and the pressure inside the space decreases. Conversely, when the volume in a closed space decreases, the gas pressure increases.

·         Gases flow from areas of higher pressure to areas of lower pressure.



Lungs cannot contract or expand on their own. The pleural cavity expands so will the lungs because they are stretchable.



Inspiration (inhalation) pulls air into the respiratory system as lung volume expands and expiration (exhalation) pushes air out as lung volume declines again.



Cycle of inspiration and expiration as follows (Oellers, Online Presentation, 2012):







            Inspiration (inhalation), when we inhale our diaphragm contracts pulling muscles down, intercostal muscles contract, elevates the chest wall and expands the volume of the chest, lowering pressure in lungs, pulling in air.



            Expiration (exhalation), when we exhale muscles relax, diaphragm resumes dome shape; intercostals muscles allow chest to lower, resulting in increase of pressure in chest and expulsion of air.



10.3b Lung volumes and vital capacity measure lung function







Each breath you take represents a tidal volume of air, which is the total air, inhaled and exhaled in a single breath. Some of the air we inhale will actually reach the alveoli and become involved in gas exchange; the other will remain in the airways and is referred to as dead space volume.



The maximal volume that you can exhale after a maximal inhalation is called your vital capacity. Your vital capacity is almost 10 times your normal tidal volume at rest. The amount of additional air that can be inhaled beyond the tidal volume is called the inspiratory reserve volume. Some air will always remain in your lungs this is called your residual volume.



A spirometer can measure your lung capacity by having a person breathe normally into the device.



Lung volumes and rates of change in volume are useful in diagnosing various lung diseases, like emphysema a condition where the smaller airways lose elasticity, causing them to collapse during expiration and impairing the ability to exhale naturally.




10.4 Gas exchange and transport occur passively



Once the air enters the alveoli, gas exchange and transport occur. There are basic principles of governing the diffusion of gases to set the stage for external and internal respiration (the second and third processes of respiration).



10.4a Gases diffuse according to their partial pressures



Earth’s atmosphere contains a mixture of gases: 78% nitrogen and 21% oxygen (Johnson 2012). In a mixture of gases, each gas exerts a partial pressure that is proportional to its percentage of the total gas composition. Because partial pressures in a mixture of gases are directly proportional to concentrations, a gas will always diffuse down its partial pressure gradient, from a region of higher partial pressure to a region of lower partial pressure (Johnson 2012). The exchange of oxygen and carbon dioxide between the alveoli and the blood and between the blood and the tissues, are passive. No ATP is used. The changes in partial pressures are used to exchange and transport these gases.



10.4b External respiration: The exchange of gases between air and blood







Oxygen diffused from alveoli (104mmHg partial pressure) into the blood (40mmHg of partial pressure), down its partial pressure gradient.



Carbon dioxide diffuses from blood, which is 46mmHg partial pressure into the alveoli 40mmHg partial pressure down its partial pressure gradient.





10.4c Internal respiration: The exchange of gases with tissue fluids










The body’s cells get their supply of oxygen for cellular respiration from the interstitial fluid that surrounds them. Because cells are constantly drawing oxygen from the interstitial fluid (by diffusion), the interstitial fluid needs to be replenished. This is accomplished by blood entering the capillaries. The oxygen is then diffused into the interstitial fluid. Carbon dioxide is opposite, it diffuses from the cell into the interstitial fluid and then into the capillary blood (Johnson 2012).



Both external and internal respiration occur entirely by diffusion. The partial pressure gradients that permit diffusion are maintained by breathing, blood transport, and cellular respiration (Johnson 2012). The end effect of all these processes is that homeostasis of the concentrations of oxygen and carbon dioxide of the cells is maintained.



10.4d Hemoglobin transports most oxygen molecules



Oxygen is transported in blood in two ways (Johnson 2012):



1)      Bound to hemoglobin in RBCs

2)      Dissolved in blood plasma







The presence of hemoglobin is essential for the transport of oxygen because oxygen is not soluble in water. Without hemoglobin, the tissues would not be able to receive enough oxygen to sustain life. 98% of oxygen in blood is carried bound to hemoglobin molecules in RBCs (Oellers, Online Presentation 2012). 2% of oxygen is dissolved in plasma (Oellers, Online Presentation, 2012).



Hemoglobin is a large protein molecule consisting of four polypeptide chains, each of which is associated with an iron-containing heme group that can bind oxygen (Johnson 2012). Oxyhemoglobin is formed because the four-heme groups bind four oxygen molecules at a time.



This is represented as:



Hb                               +          O2                   =          HbO2

Hemoglobin                            Oxygen                       Oxyhemoglobin



This formula is dependent on the partial pressures of oxygen in plasma. When the partial pressure increases in the lungs, oxygen attaches to hemoglobin and is transported in arterial blood (Johnson 2012). When the partial pressure decreases at the tissues, oxygen detaches from hemoglobin.







Other factors affect oxygen attachment to hemoglobin (Johnson 2012):



·         Binds efficiently with a neutral pH

·         Cool temperatures (similar to conditions in the lungs)

·         Affected by carbon monoxide



10.4e Most Carbon Dioxide is transported in plasma as bicarbonate



Cellular metabolism produces carbon dioxide as a waste product. Blood is used to transport carbon dioxide away from tissues and back to the lungs so that it can be removed. Carbon dioxide is diffused into the blood by the tissues because the partial pressure of carbon dioxide is higher in the tissues in the blood.



Carbon dioxide is transported in three ways (Johnson 2012):



1.      Dissolved in blood plasma

2.      Bound to hemoglobin

3.      In the form of bicarbonate



Hemoglobin can transport oxygen and carbon dioxide molecules at the same time because the two gases attach to different sites.



Almost all carbon monoxide produced by the tissues is converted to bicarbonate prior to transport.70% of carbon dioxide is converted to and transported in the plasma as bicarbonate which is used as a buffer (absorbs and releases hydrogen to moderate pH. Bicarbonate from carbon dioxide forms inside of RBCs, but quickly diffuses out of the RBCs and is transported back to the lungs and dissolved in plasma.



Hydrogen ions formed with the bicarbonate stay inside the RBCs and bind to hemoglobin. Their attachment weakens the attachment between hemoglobin and oxygen molecules and cause hemoglobin to release more oxygen. The presence of carbon dioxide enhances the delivery of oxygen to the sites where it is most likely to be needed.


As carbon dioxide is removed by breathing, the bicarbonate and hydrogen ions formed in the peripheral tissues to transport carbon dioxide are removed as well.



10.5 The nervous system regulates breathing



Breathing depends on contractions from the skeletal muscles that are activated by motor neurons. Breathing is controlled by the nervous system, which regulates the rate and depth of breathing to maintain homeostasis of carbon dioxide, hydrogen and oxygen.



10.5a A respiratory center establishes rhythm of breathing







The respiratory center is positioned at the medulla oblongata located in an area near the base of the brain and establishes basic breathing patterns (Oellers, Online Presentation 2012). The respiratory center is a group of nerve cells that automatically generate a cyclic pattern of electrical impulses every 4 to 5 seconds. These impulses stimulate the skeletal muscles to contract, causing the rib cage to expand, the diaphragm to pull downward as we inhale. As we inhale, the respiratory center receives sensory input from stretch receptors in the lungs. These receptors monitor the degree of inflation of the lungs and sever to limit inhalation and initiate exhalation. When the nerve impulses from the respiratory center to the muscles end, the respiratory muscles relax, the rib cage returns to its original size, the diaphragm moves upward again and we exhale.





10.5b Chemical receptors monitor carbon dioxide, hydrogen and oxygen levels



The body modifies the rate and depth of breathing to maintain homeostasis. Under normal circumstances the regulation of breathing centers to maintain homeostasis of carbon dioxide, hydrogen and oxygen with the main emphasis on carbon dioxide (Johnson 2012).



Certain cells in the medulla oblongata detect changes in the hydrogen concentration of the cerebrospinal fluid (the interstitial fluid around the cells in the brain). A rise in carbon dioxide increases hydrogen and increases arterial blood. Receptor cells detect elevated hydrogen concentrations and transmit signals to the respiratory center, resulting in us breathing more frequently and more deeply, exhaling more carbon dioxide and lowering blood levels of the gas back to normal.



The aortic and carotid bodies are receptors that detect changes in oxygen concentration in the arterial blood. If oxygen falls, by at least 20% these receptors are activated and will signal the respiratory center to increase the rate and depth of breathing in response to sufficiently lowered arterial oxygen.



The rate and depth of normal breathing is determined by the need to get rid of carbon dioxide rather than the need to obtain oxygen (Oellers, Online Presentation, 2012).





10.5c We can exert some conscious control



Conscious control resides in the cerebral cortex. The ability to modify our breath gives us the ability to speak and sing (Johnson 2012). We can even hold our breath for a minute, but we are not able to override automatic regulatory mechanisms, conscious control will be overpowered every time.



10.6 Disorders of the respiratory system



Many factors can lead to disorders of respiration like conditions that reduce airflow or gas exchange, infections by microorganisms, cancer, diseases of other organs such as congestive heart failure, and genetic diseases.



10.6a Reduced air flow or gas exchange impedes respiratory function



Respiration depends on the flow of air between the atmosphere and the alveoli and on the diffusional exchange of gases across the alveolar and capillary walls. Any factor that impairs these activities impedes respiratory function.



10.6a, 1 Asthma: Spasmodic contraction of bronchi



Asthma is a spasmodic contraction of bronchial muscle, bronchial swelling, and increased production of mucus (Johnson 2012). An asthma attack causes partial closure of the bronchi, making breathing difficult. Symptoms of an asthma attack include coughing while exercising, shortness of breath, wheezing and a sense of tightness in the chest. Symptoms can be triggered by viruses, air particles, allergies, exercise, tobacco smoke and air pollution.



Most asthma attacks are caused by a hyperactive immune system. When a person with asthma breathes in allergens, the body reacts with excessive production of immunoglobulin E. The IgE stimulates mast cells in the lungs, to release chemical weapons such as histamine, leading to excessive inflammation and constriction of bronchiolar smooth muscle.



Treatments focus on preventing attacks by isolating the cause and avoiding it when possible.



10.6a, 2 Emphysema: Alveoli become permanently impaired







Emphysema is a chronic disorder involving damage to the alveoli (Johnson 2012). Connective tissue in the smaller airways is destroyed resulting in airways that are less elastic, do not stay open properly and tend to collapse during exhaling. The high pressures in the lungs damage the fragile alveoli.



Most cases of emphysema are associated with smoking or long-term exposure to air pollutants.




10.6b, 3 Bronchitis: Inflammation of the bronchi



Bronchitis refers to inflammation of the bronchi, resulting in a persistent cough that produces large quantities of phlegm (Johnson 2012). Bronchitis can be either acute or chronic depending on if you smoke or live in a highly polluted area.



Symptoms include wheezing, breathlessness and a persistent cough that yields yellowish or greenish phlegm.



Acute bronchitis can be treated by humidifying the lungs, drinking plenty of fluids, and taking antibiotics if bacteria caused the infection.



10.6a, 4 Cystic fibrosis: An inherited condition



Cystic fibrosis is an inherited condition in which a single defective gene causes the mucus-producing cells in the lungs to produce a thick, sticky mucus (Johnson 2012). This disease affects organ systems. In the lungs, the thick mucus impedes airflow and provides a site for bacteria to grow. Treatment includes physical therapy to try to dislodge the mucus and keep the airways open.



10.6b Microorganisms can cause respiratory disorders



Because the lungs are moist, warm and covered in a thin layer of fluid they are prone to infection. If microorganisms infect the lungs, serious diseases can be caused like pneumonia, tuberculosis and botulism.



10.6b, 1 Colds and the flu: Common viral respiratory tract infections



Viruses cause both colds and the flu. A cold is usually an upper respiratory infection that includes symptoms like coughing, runny nose, nasal congestion and sneezing. The flu is a virus of the influenza family that include symptoms like a sore throat, fever and a cough, sometimes accompanied by aches and chills, muscle pains, and headache. There is no medical treatment for either of them. Rest and plenty of fluids are the best prescription.



The same person can catch colds and the flu repeatedly. The reason is that these viral infections evolve rapidly, so that each year they are just a little bit different from the previous year and so the immune system does not recognize them.



10.6b, 2 Tuberculosis: Bacterial infection scars the lungs



Tuberculosis (TB) is an infectious disease caused by the bacterium Mycobacterium tuberculosis. People pass the infection airborne by sneezing or coughing. In most cases, the immune system fights off this disease, but it can leave a scar on the lungs.



Symptoms include coughing, chest pain, shortness of breath, fever, night sweats, loss of appetite, and weight loss. A chest X-ray can reveal lung damage, such as cavities in the lungs or old infections that have healed, leaving scarred lung tissue. A skin test called the tuberculin test can indicate whether someone has been exposed to the infection.



10.6b, 3 Botulism: Poisoning by bacterial toxin



Botulism is a form of poisoning caused by a bacterium, Clostridium botulinum, occasionally found in improperly cooked or preserved foods (Johnson 2012). This bacterium produces a toxin that blocks the transmission of nerve signals to skeletal muscles, including the diaphragm and intercostals muscles.

Symptoms will appear 8 to 36 hours after eating contaminated food. You may have a hard time swallowing and speaking, double vision, nausea, and vomiting.



If botulism is not treated, it can be fatal because it paralyzes the respiratory muscles.



10.6c Lung cancer is caused by proliferation of abnormal cells







Cancer is the uncontrolled growth of abnormal cells (Johnson 2012). Cancer in the lungs impair the normal function of the lungs and can impair the movement of air in the airways, exchange of gases in the alveoli and the flow of blood in pulmonary blood vessels.



Lung cancer takes years to develop and is associated with smoking. Symptoms include chronic cough, wheezing, chest pain and coughing up blood. Lung cancer is highly preventable if you do not smoke, know the conditions of your work environment, and have your home inspected for radon gas.



10.6d Pneumothorax and atalectasis: A failure of gas exchange



A pneumothorax is collapse of one or more lobes of the lungs (Johnson, 2012). The most common cause is a penetrating wound of the chest that allows air into the pleural cavity around the lungs, but can also occur because of disease or injury to a lung. Pneumothorax can be life threating because of the inability to inflate the lungs, which results in a reduced exchange of oxygen and carbon dioxide.



Treatment requires repairing the damage to the chest wall or lungs and removing the air from the pleural cavity.



Atalectasis refers to a lack of gas exchange within the lung because of alveolar collapse or a buildup of fluid within alveoli (Johnson 2012). This can be caused by a complication of surgery or the amount of surfactant is deficient.



Treatment involves finding and reversing the underlying cause.



10.6e Congestive heart failure impairs lung function



Congestive heart failure is a cardiovascular condition in which the heart gradually becomes less efficient and can eventually impair lung function.



 Congestive heart failure begins when the heart fails as a pump, this can cause high blood pressure, increase the diffusional distance and reduces diffusion of gases.



Treatments focus on reducing this fluid buildup by helping the body get rid of fluid and improving the heart’s pumping action.





REFERENCES



            Johnson, M. D. (2012, 2010, 2008). Human Biology: concepts and current issues, sixth edition. Pearson Education, inc.; Benjamin Cummings.

            Oellers, J. (n.d). Online Presentation: Ch. 10 The Respiratory System: Exchange of gases. Retrieved April 14, 2012, from http://lblackboard.yc.edu/webapps/portal/frameset.jsp?tab_tab_group_id=_2_1&url=%2Fwebapps%2Fblackboard%2Fexecute%2Flauncher%3Dcourse%26id%3D_43466_1

                Science News (April 13, 2012).Implantable medical device is designed to warn patients of impending heart attack. Retrieved April 14, 2012 from http://www.sciencedaily.com/releases/2012/04/120413145305.htm