Sunday, April 15, 2012

Biology Compilation Unit 3


Table of Contents:
The Skeletal System
Bones
Bone Development
Repair and Remodeling of Bones
Bone Shapes
The Axial Skeleton
The Appendicular Skeleton
Cartilage
Ligaments
Joints
Movement of the Skeleton

The Muscular System
Structure of a Muscle
Contraction
ATP

Blood
Function
Composition
Red Blood Cells
White Blood Cells
Platelets
Homeostasis
Blood Typing

The Cardiovascular System
The Heart
Arteries
Capillaries
Veins
Circulation

The Immune System
Bacteria
Viruses
Prions
Health Risk Factors
The Lymphatic System
Blocking Pathogens and Keeping Them Out
Non-Specific Defenses
Specific Defense Mechanisms
The Five Classes of Antibodies
Medical-Initiated Immunity
Innappropriate Immune Responses

Respiration
The Upper Respiratory Tract
The Lower Respiratory Tract
Lungs
Breathing
Measuring Lung Capacity
Gas Exchange
Regulations of Breathing


The Skeletal System












The skeleton's function in the body is to support it, allow movement, protect it, and less commonly known, allow for the formation of blood cells and mineral storage. It consists of three types of connective tissue: bones, ligaments and cartilage.



Bones

There are 206 bones in the skeleton. Bones are hard inorganic matrices of calcium salts.



Spongy bone, found at the top of the epiphysis of each bone, carries the appearance of a very porous sponge. Trabaculae give the spongy bone this look. The purpose of spongy bone is to give the bone a light, but strong support.






Compact bone forms the shaft of the bone and covers each end of the bone. It is denser than spongy bone.

Bone also consists of cells called osteocytes. Osteocytes, found in compact bone, are enclosed by calcium phosphate deposits. They are arranged in cylindrical rings called osteons (or Haversian systems). Haversian canals bring the osteons their nutrients from blood diffusion via blood vessels and nerve fibers.





Bone Development

Chondroblasts are cells that form cartilage. In fetal development, chondroblasts form hyaline cartilage.

Osteoblasts are carried in the blood vessels to form bone during childhood.

Osteoclasts break down mature bone to remodel and repair it.

Osteocytes are mature bone cells.








Repair and Remodeling of Bones

Bones constantly undergo remodeling through life. Osteoclasts break down the bone and osteoblasts rebuild it. Diet, exercise and age can change the shape, size and strength of bones.

Parathyroid Hormone (PTH) removes calcium from the bone and stimulates osteoclasts to dissolve the bone. Calcitonin stimulates osteoblasts, removing calcium and phosphate from the blood and putting it into the bone.

When a bone is broken, a hematoma is formed. A hematoma is a mass of clotted blood. Fibroblasts and chondroblasts form a callus and then osteoclasts remove dead fragments of bone. Osteoblasts then form new bone out of the callus.



Bone Shapes

Long bones are bones used for larger movement. They are long and cylindrical and have heads, such as the femur. The heads of these bones are called the epiphysis.

Short Bones are for small, complex movements. Examples of short bones are the carpals and tarsals.

Flat Bones protect organs. The skull, ribs, scapula, sternum and pelvic girdle are examples of flat bones.

Irregular bones include the vertebrae and some facial bones.

Sesamoid bones are small bones within tendons, such as the patella.






The Axial Skeleton: The Skull, Vertebral Column, Ribs and the Sternum

The Skull: Temporal bone, parietal bone, frontal bone, occipital bone, sphenoid bone, ethmoid bone, lacrimal bone, nasal bone, zygomatic bone, maxilla, mandible, palatine bone, vomer bone.




The Vertebral Column: 7 Cervical vertebrae, 12 thoracic vertebrae, 5 lumbar vertebrae, 5 fused sacral vertebrae, 4 fused coccygeal vertebrae.




There are 12 Ribs and the sternum is the breastbone (three bones that are fused together).




The Appendicular Skeleton: The Pectoral Girdle, Pelvic Girdle and Limbs

The Pectoral Girdle (shoulder) includes the clavicle and scapulas.




The pelvic girdles (hips) include the coxal bones, sacrum and pubic bones.




Limbs include the arms (humerus, radius, ulna, wrists and hand bone) and legs (femur, tibia, fibula, ankle and foot bones)





Cartilage

Cartilage is used for support and where movement is needed in the bones. It is made of fibers and collagen. It is smooth and flexible. There are three types of cartilage, including fibrocartilage, hyaline, and elastic.



Fibrocartilage consists of collagen fibers arranged in bundles. It is best used for tension and pressure because it is able to support both well.



Hyaline cartilage is smooth and has a glossy appearance consisting of thin collagen fibers. It is found in embryonic development of the skeleton, along with covering the ends of bones to ease friction.



Elastic cartilage is more flexible, found in the outer ear, and in the epiglottis.



Ligaments

Ligaments are made of dense fibrous connective tissue used to connect bone to bone.







Joints

Fibrous joints are immoveable.

Cartilage joints are slightly moveable and are connected by cartilage, such as the backbone)

Synovial joints are freely moveable, such as hinge joints (like the jaw) and ball and socket joints (like the hip). Several factors help synovial joints move. The joint capsule holds the synovial membrane, which secretes a lubricating fluid, and a hyaline cartilage, which cushions the joint.



Movement of the Skeleton

Abduction and adduction are the movements of the limbs to and away from the body. Abduction means to move a limb away from the body while adduction means to move the limb toward the body.



Circumduction is a cone-like movement, or to move the limb in a circle.

Rotation is the movement of a body part around its axis, such as the way the hand moves on its axis around the arm.



Flexion and extension are the movements of joints in angles, such as the leg or arm being bent or lifted at the knee and elbow. Flexion is the decrease of the angle and extension is the increase of the angular motion.

Hyperextension means to extend the limb or head beyond its anatomical position, like moving the head back to look up, or extending a leg behind the body.



The ulna and radius are a special kind of structure in that when the arm is held in a palm-up position, the two bones are parallel. But when the palm is facing downward, the radius will cross over the ulna. These movements are classified as supination (rotating the arm so that the palm faces up or out) and pronation (rotating the arm so that the palm faces down or in).




The Muscular System







The purpose of muscles is to produce movement, contract to shorten distance between bones through the skeletal muscles and generate tension.



Synergistic muscles work together while antagonistic muscles oppose each other.



Muscles connect to bones through tendons. The origin is where the muscle joins to a bone and stays the same while the insertion is where a muscle connects across a joint. During contraction, the insertion is pulled toward the origin.








Structure of a Muscle

Muscles are composed of little bundles called fascicles. Each bundle is composed of fibrous connective tissue called fascia, which contain the muscle cells, otherwise known as muscle fibers. The fasciae all come together at the end of the muscle to form the tendon.

Muscle cells contain more than one nucleus. The cell is full of long structures called myofibrils, which are packed with the contractile proteins, myosin and actin. When myofibrils contract, the muscle cell contracts. The myofibrils are striated at intervals. In these patterns a Z-line is found. From one myofibril to a Z-line composes a sarcomere. The sarcomeres contain myosin and actin. Actin filaments are linked to the Z-line and myosin filaments are located within the sarcomeres. Myosin filaments are thick while actin filaments are thin.







Contraction

Skeletal muscle is activated by a nerve, which increases the calcium by the contractile proteins. Motor neurons secrete acetylcholine, a neurotranspmitter, or a chemical that excites the muscle cells. T-tubles transmit the electrical impulse into the cell. The sarcoplasmic reticulum is like the endoplasmic reticulum of other cells except for its shape. It stores ionic calcium.

When a muscle contracts, the sarcomeres shorten and the thick and thin filaments slide past each other in the sliding filament mechanism. The thin filaments are made of two strands of actin molecules spiraling around each other. The thick filaments are individual molecules of myosin, shaped like the head of a golf club. The heads almost touch the actin, but when the muscle relaxes, they don't contact.

In contraction, the myosin connects with the thin filaments to form a cross-bridge between them, pulling the actin towards the center of the sarcomere.

Troponin and tropomyosin are another two proteins connected with actin and myosin. Together the two form troponin-tropomyosin complex. Calcium binds to troponin and the complex exposes the myosin binding site so that the cross-bridges form. The myosin heads form cross-bridges with actin and bend, pulling the actin toward the center of the sarcomere.

Contraction ends when the nerve activation ends. No more calcium is released and the complex shifts back to its initial position. Calcium is pumped back into the sarcoplasmic reticulum, is removed from the troponin and the myosin binding site is covered again.







ATP

Muscles require energy in the form of ATP. It is required for both relaxion and contraction. It can be replenished by glycogen, creatine phosphate, and the aerobic metabolism of glucose, fatty acids and other molecules involved with high energy.

Blood


Function
The function of blood is to transport nutrients from the digestive system and hormones from the endocrine glands throughout the body. Blood also transports waste from cellular metabolism to the organs that dispose of it. It transports oxygen from the lungs to the rest of the body. It also regulates body temperature, the amount of water in the system, and pH levels. Lastly, it defends against infections and bleeding.


Composition
Blood is composed of 55% plasma. 90% of plasma is water, while the rest is composed of proteins, horomones, gases, nutrients and wastes, and electrolytes. Plasma helps to transport blood cells and platelets. The other 45% of blood is composed of elements, such as red blood cells (RBCs), white blood cells (WBCs) and platelets.







Red Blood Cells
Red blood cells transport oxygen and carbon dioxide. They are full of hemoglobin, a protein that binds oxygen. They also contain hematocrit, a measurement of the oxygen carrying capacity in RBCs. Red blood cells are formed in bone marrow and live for about 120 days. Old or damaged RBCs are destroyed in the proper organs (the liver and spleen) by large blood cells called macrophages. During the process of phagocytosis, the macrophages surround and engulf the red blood cell.








Stem cells divide into various blood cells and platelets. They can become erythroblasts, myeoblasts, monoblasts, lymphoblasts and megakaryoblasts. After eyrthyroblasts lose their nucleus, they become a red blood cell.



Red blood cell production is regulated by erythropoietin, a horomone secreted by the kidneys when the oxygen in the cells fall. Erythropoietin is transported to the red bone marrow to stimulate stem cells to produce more RBCs.






White Blood Cells

White blood cells (or leukocytes) also come from stem cells in bone marrow. They defend the body against infection and regulate the inflammitory reaction. The stem cell is reduced into myeoblasts, which reduce into neutrophils, eosinophils, and basophils, all of which are granular leukocytes.



Neutrophils, the most abundant granulocyte, are the first to fight infection by surrounding and engulfing foreign cells. Eosinophils only make up about 2-4% of the white blood cells, generally defending against large parasites by surrounding them and shooting digestive enzmes into them. They also moderate allergic reactions. Basophils are the rarest white blood cell, secreting a histamine for the inflammitory response.

Other stem cells can become monoblasts, which become monocytes, and lymphoblasts, which become lymphocytes. These are agranular leukocytes. Monocytes go into body tissues where they go through phagocytosis to get rid of invading cells. They're active during chronic infections and viruses or bacterial parasites. Lymphocytes are part of the immune response, classified into B and T lymphocytes.


Platelets
Platelets make up less than 1% of the blood. They come from megakaryocytes in the bone marrow. They stay in the bone marrow and help in clotting and repair.


Homeostasis
Homeostasis prevents blood loss in three stages. The first is a vascular spasm, where the blood vessel constricts to reduce blood flow. The second is the formation of a platelet plug, where platelets stick together and form a plug around the damaged area. Lastly, a clot is formed by soluble fibrinogen, making a mesh of fibrin to trap the red blood cells and platelets.







Blood Typing

Blood transfusions depend upon blood typing, a process that puts blood into three primary classifications under the ABO system and the Rh system. Antigens are nonself cells and antibodies are opposing proteins to antigens. Only specific antibodies can fit specific antigens. Antibodies bind to their antigens to form a complex that marks a foreign cell for destruction.

Red blood cells are classified into four types in nearly all people: A, B, AB or or. Type A blood has A antigens, B blood has B antigens, AB blood has both A and B antigens and O has neither. For example, someone with type A can receive only A or O blood because they do not possess B antigens.







The Rh factor is also used in blood typing, first found in rhesus monkeys. Most Americans are Rh positive. It's something to take into consideration for pregnant women. For example: An Rh negative woman fathers a child by an Rh positive man and the child becomes Rh positive. The fetal blood can enter the bloodstream of the mother and the mother's cells can start attacking the fetal blood cells. The mother's blood builds an immunity to the fetal blood, so that if she decides to mother other children after the first, her blood can more quickly attack the fetal blood cells.


The Cardiovascular System

The cardiovascular system consists of the heart and blood vessels (veins, arteries and capillaries).


The Heart

Surrounded by a fibrous sac called the pericardium, the heart consists mostly of muscle. It has three layers: The epicardium ( the thin outermost layer of epithelial and connective tissue), the myocardium (the thick cardiac muscle) and the endocardium (the thin innermost layer of endothelial tissue).

The heart consists of chambers and valves to pump blood. There are four chambers, two atria and two ventricles. Blood enters from the rest of the body into the right atrium. It then passes through the right atrioventricular (AV) valve into the right ventricle. Blood returning from the lungs enters the left atrium, goes through the left atrioventricular valve into the left ventricle. The valves prevent backflow from the ventricles into the atria.

From the left ventricle, blood flows through the aortic semilunar valve into the aorta, which is the largest artery in the body. From the right atrium, the blood is deoxygenated and goes through the right atrioventricular valve into the right ventricle, which pumps blood through the pulmonary semilunar valve into the pulmonary trunk, which goes to the lungs.





Arteries

As blood flows from the heart, it goes through the arteries. Arteries carry blood away from the heart. They have thick, three layered walls (from inner to outer, the endothelium, smooth muscle, and connective tissue). Arteries also carry blood under high blood pressure. The blood then goes into arterioles, or little arteries. It then travels through precapillary sphincters, much like little gates into the capillaries.


Capillaries

Capillaries are the sites where blood exchanges solutes and water with other cells of the body. They are the smallest blood vessels, consisting of one cell-layer thickness. They are also porous, as they are composed of squamous epithelium. Capillary beds are networks of capillaries.


Veins

After the blood exits the capillaries, it goes into the veins, which carry the blood back to the heart. Veins have three layers like arteries, but their lumen is bigger and they have high distensibility. Veins also serve as a blood-volume reservoir, containing almost two-thirds of the body’s blood so that if the body becomes dehydrated, the heart will still have enough blood to pump to keep the blood pressure consistent.


Skeletal muscles move the blood back to the heart by squeezing the veins. One way valves permit the blood flow. However, varicose veins can occur when the leaflets of the valves don’t meet, and the valves allow the blood to flow back into the veins so that they enlarge. This generally occurs in people who stand on their feet a lot in the legs and feet.

Circulation

The blood is circulated through the body for many reasons, as it regulates temperature, carries water, immune-system cells, oxygen, carbon dioxide, nutrients and transfers waste out of the body.


The Immune System

Everything around us is covered in living organisms, some that are beneficial and some that are harmful. Pathogens are harmful and cause disease. They include bacteria, fungi and parasites, viruses and prions.

Bacteria
Bacteria are single-celled living organisms that do not have a nucleus, but require raw materials to maintain life and grow. Beneficial bacteria have many functions, such as lining our digestive tract to draw energy from the food we eat. Harmful bacteria can cause pneumonia, tonsillitis, tuberculosis, botulism, toxic shock syndrome, syphilis and other diseases. They can be treated with antibiotics usually.
Viruses
Viruses are small infections agents, smaller than bacteria. They cannot grow on their own or reproduce outside of a host cell. They use their host cell's organelles to produce more viruses. They can cause AIDS, hepatitis, encephalitis, rabies, influenza, colds, warts, chicken pox, etc.
Prions
Prions are infectious proteins, misfolded brain proteins. One prion produces another, which produces another, etc. The brain cell infected by prions can die and burst, releasing more prions. They are resistant to cooking, freezing and drying. Prions cause bovine spongiform encephalitis, more commonly known as mad cow disease and Creutzfeld-Jakob disease.

Health Risk Factors
Certain factors can determine the dangers of pathogens and the health risks they cause. How easily they are passed from one person to another is one, along with how they can be passed (airborne, fecal-oral or through bodily fluids). Lastly, the damage done by the infection is used to determine the harm of pathogens.

The Lympatic System


The Lympatic System defends the body. It helps maintain the blood volume and transports fats and fat-soluble vitamins from the digestive system to the cardiovascular system. Lymph is found in the lymphatic system, a milky fluid that carries white blood cells, proteins, fats and sometimes bacteria and viruses. Lymphatic vessels carry the lymph throughout the system. The lymph nodes clean the lymph, removing microorganisms, cellular debris and abnormal cells. Lymph nodes are found in clusters, such as under the armpit, parts of the digestive tract, neck and groin. Macrophages and lymphocytes remove the microorganisms from the lymph.
The spleen cleanses the blood, containing red and white pulp. The red pulp contains macrophages that break down microorganisms and old or damaged red platelets. The white pulp contains lymphocytes to destroy foreign pathogens.
The thymus gland is the site of T lymphocyte maturation. It is found in the lower neck behind the sternum. It contains lymphocytes and epithelial cells, secreting thymosin and thymopoietin.
The tonsils are masses of lymphatic tissue that filter out microorganisms that enter the throat through food or air.

Blocking Pathogens and keeping them out:
The first line of defense includes the skin, tears and saliva, ear wax, mucus, the stomach, vagina, vomiting, urination, defecation and resident bacteria.
The skin's structure, pH level and its constant rebuilding of itself factors into keeping pathogens out of the body. Keratin produces a covering in the skin and the sweat glands also produce an antibiotic as a defense.
Tears, saliva, and earwax wash away particles and entraps microorganisms. Tears and saliva contain lysozyme, an enzyme that kills certain bacteria.
Mucus traps microorganisms in certain areas of the body, such as in the digestive tract so that they can no longer move. The cells in the respiratory areas move the mucus toward our throat so we get rid of the microorganisms by coughing or sneezing.
The stomach and vagina have acidic environments, inhibiting microorganisms.
Vomiting, urination and defecation remove microorganisms from the body through the digestive tract and acid pH levels in the urine.

Non-Specific Defenses:
The second line of defense includes phagocytic cells, inflammation, natural killer cells, complement proteins, interferons and the fever.

Phagocytosis is the process of surrounding and engulfing the invader cell, then breaking it down and digesting it with lysosomes, then disposing of the waste.
Inflammation is the process of healing a tissue injury. Redness, warmth, swelling an pain are found in inflammation. Mast cells release histamine to the site of injury, dilating the blood vessels to make them leaky. Complement proteins from plasma mark the bacteria for phagocyitic destruction. Phagocytes are attracted by histamine and other chemicals released and come to break down the bacteria. The rising temperature increases the activity of the phagocytes.

Natural killer cells release chemicals that break down the cell membranes of their targets until they develop holes. The natural killer cells secrete substances that enhance the inflammatory response while their target’s nucleus disintegrates.
The complement system consists of complement proteins that remain inactive until they are activated by infection. One complement protein activates another and another and so on. They create holes in the bacterial cells, which eventually fill with water and salts until they burst.
Interferons are secreted by cells that are infested with viruses. They diffuse to healthy cells and stimulate them to produce proteins that interfere with viral production.
Fever raises the body temperature to increase metabolic rate of defense cells.

Specific Defense Mechanisms;
The third line of defense is the immune response. The immune system recognizes and differentiates its own cells from non-self cells. It remembers non-self cells in order to build up a better immunity and react more quickly to a new attack.
The Immune system targets antigens, proteins or polysaccaride molecules on surfaces of invading cells. It responds to these antigens by producing antibodies to attack the antigen. Major histocompatibility complex proteins (MHC) are the body's unique self markers that mark each cell with a type of password or a fingerprint so that the immune system bypasses them because it knows they are self cells.
B Cells produce antibodies; they are antibody-mediated immunity. They become activated when they recognize an antigen. They can produce clones of themselves which become memory cells, cells with long lifespans to be used at a future date if necessary. The also produce plasma cells, which secrete antibodies to bind to the antigens when they clone.
T cells are cell-mediated immunity, which directly attack foreign cells that carry antigens; they don't need to produce antibodies. They can release proteins that help coordinate other cells and their actions. Cell-mediated immunity protects us against parasites, bacteria, viruses, fungi, cancerous cells or any other foreign cell.

Helper T Cells stimulate other immune cells. They undergo mitosis and produce a clone to carry receptors to recognize an antigen.
Cytotoxic T cells go through the blood, lymph, and tissues to find the cells that display specific antigens, the antigens they are meant to destroy. Cytotoxic T cells are the only T cells that directly attack and destroy other cells. They release a protein called perforin into the cell to create a pore for water and salts to enter into and burst the cell. It also inserts granzyme, a poisonous enzyme to kill the cell. Cytotoxic cells also go to tumors and release toxic chemicals to the abnormal cells.
Memory T cells retain receptors for the antigen that they were initially stimulated for. Once they are reactivated by that antigen, they may form new helper T cells or new cytotoxic cells.

Cells such as macrophages and B cells are called antigen-presenting cells (APCs). They engulf and partially digest foreign particles and form fragments of antigens on their surfaces. The vesicle joins with a vesicle that contains MHC molecules, which bind to the antigen pieces and displays as an antigen-MHC complex. The cell presents a fragment of the antigens for the T cells to recognize.
If the T cell binds with the complex, it activates and begins mitosis. This is called clonal expansion, increasing the number of T cells that recognize that antigen.


The Five Classes of Antibodies:
Antibodies are classified as immuniglobulins (Ig)

IgG is the most common, found in blood and lymph, intestines and tissue fluid. They are long lived and activate the complement system.
IgM: They are the first ones released during immune responses, found in blood and lymph.
IgA: They enter areas of the bodies that are covered in a mucous membrane, like the digestive, reproductive and respiratory tracts. They neutralize infections.
IgD: Found in blood and lymph and B cells, possibly playing a role in activating B cells
IgE: Rarest, found in B cells, mast cells and basophils to activate inflammatory response by triggering histamine release.

A primary immune response is created when the immune system is first exposed to an antigen about 3 to six days after the antigen first appears. B cells to that antigen multiply and turn into plasma cells, and the amount of antibodies rise until they peak after about 10 to 12 days and level off.
A secondary immune response is faster and lasts longer. Once re-exposed tot\ the antigen, the second immune response takes only hours and reaches its peak in days.

Medical-Initiated Immunity
The medical world has taken multiple steps in helping the immune system defend the body.
Vaccines have been developed. They are the intentional exposure to a form of the antigen that doesn't produce a disease so as to develop faster immunity to the antigen that does carry disease should the body get it later on naturally. Thisa is known as active immunization.
Passive immunization is a way of giving the body protective antibodies.
Monoclonal antibodies are antibodies that are produced in laboratories as clones of a hybrid B cell. They are most popularly used in pregnancy tests, prostate cancer tests, and tests for hepatitis, influenza and HIV.
Antibiotics are toxic to kill bacteria by targeting the cell wall or capsule, but are ineffective against viruses.

Innappropriate Immune Responses
Allergies can be severe enough to require hospitalization or mild enough for common treatments. They are considered 'inappropriate” because the body reacts to allergens as if it were a pathogen, though its not. In turn, stem cells can produce histamine to the area of contact, secreting secretion of mucus. Antihistamines are treatments to mild to moderate allergic reactions.
Bee stings and food allergies go into the blood stream though, some eliciting a systemic response to where they could constrict muscle in the lungs and digestive system and dilate blood vessels. This could cause difficulty breathing, stomach cramps, swelling and circulatory collapse. Epinephrine injections dilates the airway and constricts peripheral blood vessels to prevent shock.

Autoimmune disorders are disorders in which the immune system cannot distinguish self cells from non-self cells so that the antibodies and cytotoxic T cells target the body's own tissues. Lupus is a disorder in which the body attacks its own connective tissue. Rheumatoid arthritis is in inflammation of the synovial membrane that lines certain joints where B cells produce antibodies against a protein in their cartilage.
Respiration

The respiratory system exchanges carbon dioxide and oxygen with air.

Breathing (ventilation) is the process of moving air into and out of the lungs.
External respiration is the exchange of gases between air and blood. It takes place in the lungs.
Internal respiration is the exchange of gases between blood and tissue fluids. It happens in tissues and throughout the rest of the body
Cellular respiration is the process of using oxygen to make ATP, and turn carbon dioxide into waste. It also takes place in tissues and throughout the rest of the body.

The Upper Respiratory Tract
The upper respiratory tract consists of the nose, nasal passages, and pharynx. Air goes through the nose (or mouth), then through the nasal passages, and into the pharynx, which is in the throat. The upper respiratory tract is responsible for scent receptors, warming and moistening the air, resonating the voice, and filtering out foreign particles.



Air then travels down to the lower respiratory tract, including the larynx, trachea, bronchi and bronchioles,lungs and alveoli.
The Lower Respiratory Tract
The lower respiratory tract is responsible for sound production, transporting the air to and from the lungs, and routing food and air to the appropriate places. Mucus in the respiratory tract also entraps microorganisms and cilia propels them up and out of the respiratory tract via coughing and sneezing. Smoking can cause damage to the cilia.


The Lungs
The lungs are in the thoracic cavity. They are covered in pleural membranes and in between them and their membranes is a pleural cavity where fluid reduces friction between the lungs and chest wall during respiration. The right lung has three lobes and the left has two. Inside each lobe is a branching tree of bronchioles. The bronchioles contain clusters of aveoli, which are air filled sacs. This is where the gases are exchanged.

In the pulmonary capillaries in the lungs, blood comes close to the air in the aveoli, allowing oxygenated blood to be collected and brought back to the heart.


Breathing
In a relaxed state, the diaphragm and intercostal muscles are relaxed. Inspiration (inhailing) brings air into the lungs. The lungs expand and the diaphragm contracts, pulling the muscle down. The intercostal muscles (between the ribs) contract and the chest wall elevates. The pressure in the lungs lowers and air goes in. Expiration (exhaling) pushes air out of the lungs. The muscles relax, the diagram lowers and the intercostal muscles lower. The pressure in the chest increases and air goes out.

Measuring Lung Capacity
The amount of air inhaled and exhaled per breath is measured as the tidal volume. The air that stays in the airways but does not go through gas exchange is called dead space volume. The maximum amount of air that can be inhaled is measured as the vital capacity. Beyond the tidal volume is the inspiratory reserve volume. Conversely, the amount of air that goes beyond the tidal volume is called expiratory reserve volume. And the amount of air that remains in the lung after even forceful expiration is called residual volume. Each of these volumes can be measured by a spirometer.

Gas Exchange
Partial pressure is the pressure exerted by each gas in a mixture of gases. It is proportional to its percentage of total gas composition. It is represented as P and is measured in mm Hg.
Between air and blood, O2 is diffused from aveoli into blood (104mmHg) down the partial pressure gradient. In exchange, CO2 diffuses from blood (46mmHg) into the aveoli (40mmHg) down the partial pressure gradient.
Between tissue fluids and gases, O2 diffisues from the capillaries to the intersitial fluid to the cells down the pressure gradient. The process reverses with CO2.
Most of the O2 is transported by hemoglobin in red blood cells. The rest is dissolved in plasma. In the same, most of the CO2 is transported in plasma as bicarbonate. 70% of it is converted and used as a buffer to moderate pH. 10% is dissolved in the plasma and 20% of it binds to hemoglobin for transport.

Regulation of Breathing
The nervous system regulates breathing because the respiratory system is located in the medulla oblongata. The medulla oblongata generates a pattern of electrical impulses every 4-5 seconds, which stimulate the intercostal muscles to contract. When the stretch receptors in the lungs send the impulses back to the respiratory center, the lungs relax.
The medulla oblongata also monitors CO2, H+ and O2 levels. A rise in the PCO2 in the blood will cause a rise in H+ in the cerebrospinal fluid, and the medulla oblongata raises the respiratory rate. If the PO2 falls by at least 20%, the aortic and carotid bodies will increase the rate and depth of breathing to lower the PO2.
We are able to control our breathing to an extent. We can hold our breath for awhile, but the medulla oblongata will take over after a certain point. We can also moderate our breath to speak and sing.
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