Cardiovascular System: Heart and Blood Vessels
Cardiovascular System: Blood
Lymphatic System and Immunity
AIDS
Cardiovascular System: Heart and Blood Vessels
The cardiovascular system consists of the heart (which pumps blood) and the blood vessels (through which the blood flows.)
http://www.niaaa.nih.gov/NR/rdonlyres/BF321698-FDCA-443F-9D66-6E00F445CDAF/0/270f1.gifThe purpose of the circulatory system is to service the cells. Cells are bathed with tissue fluid. The blood exchanges substances with the tissue fluid and not with the cells directly. The blood removes waste from the tissue fluid but also brings oxygen and the nutrients the cells need to survive.
The lymphatic system assists the cardiovascular system because the lymphatic vessels collect excess tissue fluid and return it to the cardiovascular system. Water collects in the tissues during the exchange of blood and tissue fluid. The water enters the lymphatic vessels which start in the tissues and end at the cardiovascular veins in the shoulder. As soon as fluid enters the lymphatic vessels, it is called lymph. Lymph is a fluid tissue as is blood.
http://www.healingdaily.com/exercise/lymphatic-system-dependent-on-detoxification.jpgThere are 3 types of blood vessels: arteries, veins, and capillaries. Each has a specific and appropriate function.
Arteries:
- Have 3 layers: inner (endolithium) , middle (smooth muscle and elastic tissue) and outer (connective tissue)
- Strong arterial walls support when the blood enters, elasticity allows for expansion
- Take oxygenated blood from the heart to the tissues (except pulmonary artery)
http://encyclopedia.jrank.org/Cambridge/entries/images/artery%201.jpgVeins:
- Have 3 layers with less smooth muscle in middle layer and less connective tissue in outer layer than an artery, thinner than an artery.
- Have valves which allow blood flow only toward the heart, found in veins that carry blood against the force of gravity
- Act as a blood reservoir
- Carry deoxygenated blood to the heart (except pulmonary vein)
http://www.medem.com/MEDEM/images/ama/ama_preventive_heartdiseaseandstroke_lev20_circulatorysystem-venous_01.gifCapillaries:
Aterioles (small arteries visible to the naked eye) branch into capillaries. A capillary is an extremely narrow, microscopic tube with a wall composed of endolithium and a basement membrane. Capillary beds (networks of capillaries) are present in all regions of the human body. Only certain capillaries are open at certain times. When a capillary bed is closed, the precapillary sphincter contracts, and the blood moves from the arteriole to the venule (small veins that drain blood from capillaries) by way of an arteriovenous shunt.
http://academic.emporia.edu/aberjame/struc_geo/appalach/app09.jpgThe heart is a cone-shaped, muscular organ located between the lungs, directly behind the sternum. The major portion of the heart s called the myocardium, which consists largely of cardiac muscle tissue. Myocardium is serviced by the coronary artery and cardiac vein, not by the blood it pumps. The muscle fibers of myocardium are branched and tightly joined by intercalated disks. The heart is surrounded by the pericardium: a thick, membranous sac that supports and protects the heart. The inside of the pericardium secretes a lubrication fluid and the pericardium slides smoothly over the surface as the heart pumps.
http://www.nlm.nih.gov/medlineplus/ency/images/ency/fullsize/1097.jpgThe septum separates the heart into a right and left side. The heart itself has 4 chambers: the right and left atrium and the right and left ventricles. Heart valves keep blood flowing in the right direction and prevent backward movement. The valves that lie between the atria and the ventricles are called the atrioventricular valves. One is a tricuspid valve (hence the name) and the other is the mitral valve (named for resemblance to a mitre.) They are supported by strong, fibrous strings called the chordae tendineae. The chordae are attached to the muscular projections of the ventricular walls (papillary muscle) which support the valves and prevent them from inverting when the heart contracts. The other two valves are the semilunar valves that lie between the ventricles and their attached vessels. The semilunar valves are named for their attached vessels: the pulmonary valve and the aortic valve.
http://www.nlm.nih.gov/medlineplus/ency/images/ency/fullsize/9380.jpgAlthough the presence of intercalated disks allows both the atria and the ventricles to contract simultaneously, we can trace the passage of blood through the heart as follows:
- The superior vena cava and the inferior vena cava which carry O2 poor blood enter the right atrium
- The right atrium sends blood through the tricuspid valve to the right ventricle
- The right ventricle sends blood through the pulmonary semilunar valve into the pulmonary trunk, which carries O2 poor blood, divides into 2 pulmonary arteries which go to the lungs
- 4 pulmonary veins which carry O2 rich blood enter the left atrium
- The left atrium sends blood through the the mitral valve to the left ventricle
- The left ventricle sends blood through the aortic semilunar valve into the aorta to the body proper
http://www.medicalook.com/diseases_images/heart-diseases1.jpg Each heartbeat is controlled by a cardiac cycle. When the heart beats, the two atria contract at the same time, then the two ventricles contract at the same time. Then all chambers relax. Systole (the working phase) refers to the contraction of the chambers. Diastole (the resting phase) refers to the relaxation of the chambers. The normal adult heart rate is between 60-80 beats per minute.
The sounds of a heart beat are centered around the closing of the valves. The "lub" sound occurs when the increasing pressure forces the cusps of the AV valve to slam shut. The "dup" sound occurs when the ventricles relax and the blood in the arteries pushes back, closing the semilunar valves.'' A heart murmur is often due to ineffective valves. There is a distinctive swishing sound after the "lub." Faulty heart valves can usually be surgically corrected.
http://static.howstuffworks.com/gif/adam/images/en/heart-beat-picture.jpg The rhythmical contraction of the atria and ventricles is due to the internal conduction system of the heart. Nodal tissue (has both muscular and nervous characteristics) is a unique type of cardiac muscle located in 2 regions of the heart. The SA (sinoatrial) node is located in the upper dorsal wall of the right atrium; the AV (atrioventricular) node is located in the base of the right atrium near the septum. The SA node initiates the heartbeat and sends out an excitation impulse every 0.85 seconds; this causes the atria to contract. When impulses reach the AV node, there is a slight delay that allows the atria to finish their contraction before the ventricles begin their contraction. The signal for the ventricles to contract travels from the AV node throught the 2 branches of the AV bundle before reaching the numerous and smaller Purkinje fibers. The AV bundle, its branches, and the Purkinje fibers work efficiently because gap junctions at intercalated disks allow electrical current to flow from cell to cell.
The SA node is called the pacemaker because it usually keeps the heartbeat regular. If it fails to work properly, the heart still beats due to impulses generated by the AV node, but it will beat slower. An artificial pacemaker is implanted to correct this condition.
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The body also has an external way to regulate heartbeat. The cardiac control center in the medulla oblongata, a portion of the brain that controls internal organs, can alter the heartbeat by way of the parasympathetic or sympathetic nervous system. The hormones epinephrine and norepinephrine can also stimulate the heart.
http://www.medicalook.com/systems_images/Medulla_Oblongata.jpg
An electrocardiogram (ECG) is a recording of the electrical changes that occur in the myocardium during a cardiac cycle. Body fluids contain ions that conduct electric currents and electrical changes in the myocardium can be detected on the skin's surface. When an ECG is taken, electrodes placed on the skin are connected by wires to an instrument that detect myocardium electrical changes. Various types of abnormalities can be detected by an ECG. Ventricular fibrillation is an uncoordinated contraction of the ventricles and can be caused by injury or drug overdose. Defibrillation may help the SA node reestablish a coordinated beat.
http://www.clarian.org/ADAM/doc/graphics/images/en/1135.jpg
Pulse rate equals heart rate. The surge of blood entering the arteries causes their elastic walls to stretch, then immediately recoil. This rhythmic expansion and recoil of an arterial wall can be felt as a pulse in any artery that runs close to the body's surface. Pulse is normally taken in the radial artery, but can be taken in the brachial or carotid if necessary. Use your fingers and not your thumb, the thumb has its own pulse.
http://web.indstate.edu/thcme/PSP/eLabs/pulse1.gif
Blood pressure is the pressure of blood against the wall of a blood vessel. A sphygmomanometer (blood pressure instrument) is used to measure blood pressure in the brachial artery. The highest arterial pressure (systolic) occurs during ejection of blood from the heart. The lowest arterial pressure (diastolic) occurs while the ventricles are relaxing.
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The sounds you hear while taking blood pressure are called Korotkoff sounds, named after Dr. Nikolai Korotkoff, a Russian doctor who discovered them.
http://faculty.washington.edu/kepeter/119/images/bp_reading1.jpgBlood flow is slow in the capillaries. The slow progress allows time for exchange of substances between bloood and tissue. Blood pressure is minimal in the venous system, even so, velocity of flow increases in veins. Venous return is dependent on 3 factors: The skeletal muscle pump (dependent on skeletal muscle contraction) compresses the weak venous walls and cause the blood to move past a valve. Once past the valve the blood cannot return. A respiratory pump (dependent upon breathing) works as we inhale the chest expands which reduces pressure in the thoracic cavity. Blood flows from the higher pressure to the lower pressure. When we exhale, the process reverses, but the valves prevent backward flow.
http://www.lib.mcg.edu/edu/eshuphysio/program/section3/3ch10/3c10img/page6.jpgBlood flows in 2 circuits: the pulmonary circuit, which circulates blood through the lungs, and the systemic circuit, which serves the needs of the body tissues. Both are necessary for homeostasis.
The pulmonary and systemic circuit:
http://academic.kellogg.cc.mi.us/herbrandsonc/bio201_McKinley/f22-1_cardiovascular_sy_c.jpgThe coronary arteries serve the heart muscle itself. The coronary arteries are the first branches off the aorta. They originate just above the aortic semilunar valve and lie on the exterior surface of the heart.
http://www.texasheartinstitute.org/HIC/Anatomy/images/coronill.gifThe hepatic portal vein takes blood from the capillary bed of the digestive tract to a capillary bed in the liver. The blood in the hepatic portal vein is O2 poor, but rich in glucose and amino acids. The hepatic vein leaves the liver and enters in the inferior vena cava.
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Capillary exchange occurs by either blood pressure or osmotic pressure. At the arterial end, blood pressure is higher than osmotic pressure. Osmotic pressure is created by the presence of salts and the plasma proteins. At the venous end, osmotic pressure is higher than blood pressure.
http://www.coolschool.ca/lor/BI12/unit9/U09L08/CTFEx.gifCardiovascular disease is the leading cause of untimely death in the Western countries. Research has proved effective in improved diagnosis, treatment, and prevention. Some common cardiovascular diseases are:
- Hypertension- high blood pressure
- Aneurysm- burst blood vessel
- Atherosclerosis- accumulation of soft fatty materials, like cholesterol, beneath the artery inner linings
- Thrombus- a stationary plaque clot
- Embolus- moving plaque clot
- Thromboembolism- a clot that has moved and is now stationary
- Stroke (CVA)- small cranial arteriole bursts or is blocked
- Heart attack- portion of the heart muscle dies due to lack of O2
- Angina pectoris- partially blocked coronary artery with radiating pain
http://www.med.umich.edu/opm/newspage/images/engineerheartlg.jpg When a person has heart failure, the heart no longer pumps as it should. Heart failure is a growing problem. Often the heart is oversized because it is sagging and swollen. Sometimes a failing heart can have an abnormal rhythm and a cardioverter-defibrillator is implanted. Heart transplants are generally successful. Unfortunately, there are more patients that need hearts than donors. A left ventricular assist device is an alternative to a heart transplant. It is implanted in the abdomen and a tube passes blood from the left ventricle to the aorta. A few patients have received a total artificial heart. All recipients have been near death and have not survived very long. Hopefully technology will continue to improve.
http://www.thehindubusinessline.com/nic/055/heart.jpg
Cardiovascular System: Blood
The human body contains about 5 liters of blood and the heart pumps this amount in every beat. The functions of the blood fall into 3 categories: transport, defense, and regulation.
- Blood is the primary transport medium-delivers O2 from the lungs and nutrients from the digestive tract to the tissue where an exchange takes place. It picks up CO2 and wastes from the tissues to exchange surfaces in the lungs and kidneys.
- Blood defends the body against invasion by pathogens-certain blood cells are capable of phagocytizing and destroying pathogens and others secrete antibodies in the blood.
- Blood has regulatory functions-helps regulate body temperature by picking up heat. The salts and plasma proteins in blood act to keep the liquid content of blood high. Blood contains buffers that stabilize blood pH.
http://training.seer.cancer.gov/ss_module08_lymph_leuk/images/illu_blood_cell_lineage.jpgBlood is a tissue and contains cells and cell fragments. Collectively, the cell and cell fragments are called the formed elements. They are suspended in a liquid called plasma. Blood is classified as a liquid tissue.
The formed elements are red blood cells, white blood cells, and platelets. They are produced in red bone marrow, which occurs in most bones of a child, but only certain bones of an adult. Red bone marrow contains stem cells, which divide and give rise to the various types of blood cells. Stem cells are of interest since they can be coaxed into becoming different cells that may cure diseases.
http://static.howstuffworks.com/gif/artificial-blood-1.jpg
Plasma is the liquid medium for carrying the various substances in the blood. It also distributes heat generated as a byproduct of metabolism . About 91% of plasma is water, the remaining 9% consists of various salts and organic molecules.
http://www.ndsu.nodak.edu/instruct/tcolvill/435/plasma.gif
The most abundant organic molecules in blood are the plasma proteins. Plasma proteins take up and release hydrogen ions, regulating the blood pH to about 7.4. Plasma proteins are too large to pass through capillary walls; they remain in the blood and establish an osmotic gradient between blood and tissue fluid. There are 3 major types of plasma proteins: albumins, globulins, and fibrinogen. Albumins contribute most to plasma's osmotic pressure and combine with and help transport other organic molecules. Globulins are of 3 types: alpha, beta, and gamma. Alpha and beta combine with and help transport substances in the blood. Gamma globulins are important in fighting disease. Fibrinogen is a plasma protein that is active in the formation of blood clots.
Red blood cells (erythrocytes) are small biconcave disks that lack a nucleus when mature. Red blood cells (RBCs) are highly specialized for O2 transport. They lack a nucleus and contain many copies of hemoglobin (Hb.)
http://science.uwe.ac.uk/research/uploads/CRIB_blood_cells.jpg Hemoglobin is a pigment that makes red blood cells and blood a red color. The globin is a protein that contains 4 highly folded polypeptide chains. The heme is an iron-containing group in the center of each polypeptide chain. The iron combines reversible with O2.
http://chemistry.ewu.edu/jcorkill/biochem/HemoglobinMOM.jpg
After blood picks up CO2 in the tissues, about 7% is dissolved in plasma. Hemoglobin directly transports about 25% of CO2. The rest of the CO2 is transported as the bicarbonate ion (HCO3-) in the plasma. CO2 moves into RBCs where carbonic anhydrase speeds this reaction. The bicarbonate ion diffuses out of RBCs to carried in the plasma. The H+ binds to amino acids of the globin portion of Hb.
The RBC stem cell in the bone marrow divides and produces new cells that differentiate into mature RBCs. As red blood cells mature they lose their nucleus and acquire hemoglobin. Red blood cells live only 120 days. It is estimated the 2 million RBCs are destroyed per second and an equal number must be produced to keep the red blood cell count in balance. When red blood cells break down, hemoglogin is released. The globin portion is recycled by the body. The iron is recovered and returned to the bone marrow for reuse. The heme portion degrades and is excreted by the liver. Chemical breakdown in the heme causes a bruise to change color from red/purple to blue to green to yellow.
http://www.harunyahya.com/books/science/blood_heart/images/red_blood_cell_8.jpgRed blood cell disorders:
- Anemia-insufficient number or red blood cells or the cells do not have enough hemoglobin
- Hemolysis- rupturing of red blood cells
- Sickle Cell Anemia- a hereditary condition which the individual cell has a sickle shape and ruptures as it passes through capillaries
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White blood cells (leukocytes) differ from red blood cells in that they are larger, have a nucleus, lack hemoglobin, and are translucent unless stained. White blood cells are not as numerous as red blood cells. There are several types of white blood cells and the production of each is regulated by a protein called a colony-stimulating factor (CSF.)
http://graphics8.nytimes.com/images/2007/08/01/health/adam/9123.jpgWhite blood cells fight infection and are an important part of the immune system. Many white blood cells die within a few days, some live for months or even years. White blood cells fight infection in various ways. During phagocytosis, a projection from the cell surrounds a pathogen and literally engulfs it. Other white blood cells produce antibodies to destroy pathogens.
http://scienceroll.files.wordpress.com/2007/04/phagocytosis.jpg Granular leukocytes include neutrophils, eosinophils, and basophils.
Neutrophils account for 50-70% of all white blood cells. They have a multilobed nucleus and are called polymorphonuclear leukocytes. Neutriphils are the first responders to bacterial infection and their intense phagocytic activity is essential to destroying pathogens. Neutrophils are like vacuum cleaners because they suck up unwanted substances.
http://www.chronicprostatitis.com/images/neutrophil.jpg
Eosinophils have a bilobed nucleus and their large abundant granules take up eosin and become a red color. Not much is known about eosinophils except they increase in number in the event of a parasitic worm or allergic reaction.
http://192.107.108.56/portfolios/b/bess_n/bessthesisproject/eosinophil.jpgBasophils have a U-shaped or lobed nucleus. In the connective tissue, basophils and mast cells release histamines associated with allergic reactions. Histamines dilate blood vessels, but constrict air tubes that lead to the lungs.
http://www.funsci.com/fun3_en/blood/blood_10.gif
Agranular leukocytes include lymphocytes and monocytes.
Leukocytes account for 25-35% of all white blood cells. They are responsible for specific immunity to particular pathogens and thier toxins. There are 2 types of lymphocytes: B cells and T cells. B cells and their descendants produce antibodies. Some T cells directly destroy pathogens.
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Monocytes are the largest of the white blood cells and after taking up residence in the tissues, they differentiate into even larger macrophages except in the skin where they become dendritic cells. Macrophages and dendritic cells stimulate other white blood cells to defend the body.
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Disorders involving white blood cells:
- Severe Combined Immunodeficiency Disease (SCID)- stem cells of white blood cells lack the enzyme adenosine deaminase
- Leukemia- a group of cancerous conditions that involve uncontrolled white blood cell proliferation
- Epstein-Barr Virus (EBV)- infection of the lymphocytes, the cause of infectious mononucleosis
http://plaza.snu.ac.kr/~sklcrs/t-cell2.jpg
Platelets (thrombocytes) result from fragmentation of certain large cells called megakaryocytes in the red bone marrow. Platelets are produced at the rate of 200 billion per day. They are formed elements that are involved in the process of blood clotting (coagulation.) Also involved in clotting are the plasma proteins prothrombin and fibrinogen.
http://www.astrographics.com/GalleryPrints/Display/GP2076.jpg
When a blood vessel is damaged, platelets clump together at the site of the puncture and seal the break if it is not too extensive. A large break may require a blood clot to stop the bleeding. At least 12 clotting factors participate in the formation of a blood clot. Clot formation is initiated when platelets and damaged tissues release prothrombin activator which converts plasma protein prothrombin to thrombin. Thrombin acts as an enzyme that severs 2 short amino acid chains from each fibrinogen molecule. These activated ends join together to form fibrin. Fibrin threads wind around the platelet plug in the damaged area and provide the framework for the clot. The fibrin clot is temporary as plasmin destroys the fibrin network as soon as blood vessel repair is initiated.
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Disorders related to blood clotting:
- Thrombocytopenia-due to a low production of platelets in the bone marrow or an increased breakdown of platelets outside the bone marrow
- Thromboembolism- a formed clot in an unbroken blood vessel, if dislodged becomes an embolus
- Hemophilia- an inherited clotting disorder due ti a deficiency in a clotting factor
http://blogsci.com/images/ABO_blood_type.jpg
The designation of blood type includes whether the person has or does not have the Rh factor on the red blood cell. Rh- individuals normally do not have the antibodies to the Rh factor, but make them when exposed to the Rh factor. During pregnancy, an Rh- mother can have problems if the father is Rh+, because the child may be Rh+. If so, the mother will produce anti-Rh antibodies which may harm the child's red blood cells. This is prevented by giving the mother an Rh immunoglobulin injection no later than 72 hrs after giving birth.
Each of the human systems work together to maintain homeostasis. The cardiovascular system is of primary importance because it serves the needs of the cells. Several other systems contribute as well: the digestive, the respiratory, the nervous and endocrine, the lymphatic, and the skeletal.
Lymphatic System and Immunity
Microbes such as bacteria are widely distributed in the environment. They cover the surfaces of plants, animals, and inanimate objects. Some microbes are helpful, some are harmful. Human infectious diseases are typically caused by bacteria and viruses, collectively known as pathogens. The human body has 3 lines of defense against pathogens: barriers to entry, first responders, and specific defenses.
Bacteria are single celled prokaryotes without a nucleus. They have 3 common shapes:
- Bacillus-rod
- Coccus-spherical
- Spirillum-curved
http://www.scharfphoto.com/fine_art_prints/archives/199812-026-Staph-Bacteria.jpgViruses bridge the gap between the living and nonliving. Outside a host, viruses are essentially chemicals that can be stored on a shelf. BUt when the opportunity arises, viruses replicate inside cells and appear to be alive. Viruses are acellular, they are obligate parasites and do not live independently. Virus particles are four times smaller than bacteria. Virus has 2 parts: an outer capsid composed of protein units and an inner core of nucleic acid. A virus carries genetic information needed to reproduce. Viral genetic material does not need to be double stranded DNA or even DNA. Some viruses, like HIV, have an RNA genome. Viruses with animal reservoirs are hard to control. A virus may emerge by transport from one location to another. Viral disease are also transmitted by vectors, usually insects. Mutations allow different modes of transmissions.
http://infusionblog.com/wp-content/uploads/2007/08/virus_big.jpgPrions are proteinaceous infectious particles. They cause a group of degenerative diseases of the nervous system (wasting diseases.) Prions are proteins of unknown function in the brains of healthy individuals. Disease occurs when certain prion proteins change shape into a rogue form.
http://www.mpibpc.mpg.de/groups/grubmueller/start/people/mstumpe1/gallery/Prion.jpgThe lymphatic system consists of lymphatic vessels and the lymphatic organs. The lymphatic system has 4 main functions that contribute to homeostasis:
- Lymphatic capillaries absorb excess tissue fluid and return it to the bloodstream
- In the small intestine, lymphatic capillaries called lacteals absorb fat in the form of lipoproteins and transport them to the bloodstream
- The lymphatic system is responsible for the production, maintenance, and distribution of lymphocytes
- The lymphatic system helps defend the body against pathogens
http://www.advancedhealthhealingarts.com/images/lymphatic_drainage.jpg
Lymphatic vessels form a one-way system of capillaries then vessels then ducts that take lymph to cardiovascular veins in the shoulders. The fluid inside lymphatic vessels is called lymph. The lymphatic system has 2 ducts, the thoracic duct and the right lymphatic duct. The thoracic duct returns lymph collected from the body below the thorax, the left arm, and the left side of the head and neck into the left subclavian vein. The right lymphatic duct returns lymph from the right arm and the right side of the head and neck into the right subclavian vein.
http://training.seer.cancer.gov/module_anatomy/images/illu_lymph_capillary.jpgLymphatic organs are divided into those that are primary: red bone marrow and the thymus gland; and those that are secondary: lymph nodes and spleen. Blood cells, including lymphocytes, are produced in red bone marrow. B cells mature in the bone marrow, but T cells mature in the thymus. Lymph is cleansed in lymph nodes, while blood is cleansed in the spleen.
http://pubutils.fccc.edu:8180/slide/files/www/images/pdq/CDR0000533339.jpg- Red bone marrow- produces all types of blood cells.
- Thymus gland- located in the thoracic cavity between the trachea and the sternum; produces thymic hormones that aid in the maturation of T lymphocytes, immature T lymphocytes migrate from the bone marrow through the bloodstream to the thymus, where they mature
- Spleen-filters blood
- Lymph nodes- filter lymph
- Lymphatic nodules-concentrations of lymphatic tissue not surrounded by a capsule (such as tonsils)
- Peyer's patch- located in the intestinal wall and the appendix, attached to the cecum; encounters pathogens in the intestinal tract
- Skin and Mucous Membranes
- Chemical Barriers- sebaceous glands, lysozyme, acid pH of the stomach
- Resident Bacteria- normal flora and microbes
- Capillary changes and chemical mediators, like histamine from mast cells
- Macrophages and dendritic cells release cytokines
- Macrophages and dendritic cells phagocytize pathogens, as do neutrophils
- Blood clots seal a break in a blood vessel
http://www.chronicprostatitis.com/images/f3.jpg
The complement system is composed of a number of blood plasma proteins designated by the letter C and subscript. The complement proteins "complement" certain immune system responses. They amplify the inflammatory response because certain complement proteins can bind to mast cells and trigger histamine release and others can attract phagocytes. Other proteins join to form a membrane attack complex that produces holes in the surface and bacteria and some viruses. Interferons are proteins produced by virus infected cells as a warning to non-infected cells in the area. Interferon binds to receptors of noninfected cells, causing them to prepare for possible attack.
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Immunocell Type and Function
- B cells- produce plasma cells (produce specific antibodies) and memory cells (ready to produce antibodies in the future)
- T Cells- regulate immune response; produce Cytotoxic T cells (kill virus-infected cells and cancer cells), Helper T cells (regulate immunity), and Memory T cells (ready to kill in the future)
http://stemcells.nih.gov/StaticResources/info/scireport/images/figure61.jpgOnce the threat of an infection has passed, the development of new plasma cells ceases and those present undergo apoptosis (programmed cell death.)
The basic unit which composes antibody molecules is a Y shaped protein molecule with 2 arms. Each arm has a heavy and light polypeptide chain. These chains have constant regions located at the trunk of the Y where the sequence of the amino acids is set. The class of antibody of each individual molecule is determined by the structure of the antibody's constant region. The variable region forms an antigen-binding site and their shape is specific to a particular antigen. Memory B cells remain in the body and produce antibodies if the same antigen enters the body at a later date.
http://www.accessexcellence.org/RC/VL/GG/ecb/ecb_images/04_32_antibody.jpgThere are 5 different classes of antibodies:
- IgG-main antibody type in circulation, binds to pathogens, activates complement and enhances phagocytosis
- IgM-found in circulation, largest antibody, first antibody formed by newborn, activates complements, clumps cell
- IgA-main antibody type in secretions such as saliva and milk, prevents pathogens from attaching to epithelial cells in digestive and respiratory tract
- IgD-found on surface of immature B cells, presence signifies readiness of B cell
- IgE-found as antigen receptors on basophils in blood and on mast cells in tissues, responsible for immediate allergic response and protection against parasitic worms
http://research.chem.psu.edu/edsgroup/img/IgEstimulation.jpg
For a T cell to recognize an antigen, the antigen must be presented by an antigen-presenting macrophage, along with an human leukocyte antigen (HLA.) Activated T cells undergo clonal expansion until the illness has been stemmed. Then, most of the activated T cells undergo apoptosis. A few cells remain as memory T cells. The 2 main types of T cells are cytotoxic T cells and helper T cells. Cytotoxic T cells kill virus-infected cells or cancer cells on contact because they bear a nonself protein. Helper T cells produce cytokines and stimulate other immune cells.
http://www.wellesley.edu/Chemistry/Chem101/antibiotics/Tcell.jpg
Active immunity can be induced by vaccines when a person is well and in no immediate danger of contracting an infectious disease. Active immunity depends upon the presence of memory cells in the body. Passive immunity is needed when an individual is in immediate danger of succumbing to an infectious disease. Passive immunity is short lived because the antibodies are administered to and not made by the individual. Monoclonal antibodies which are produced by the same plasma cell, have various functions from detecting infections to treating cancer. Cytokines, including interferon, are a form of passive immunity used to treat AIDS and to promote the body's ability to recover.
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Allergic responses occur when the immune system reacts vigorously to substances not normally recognized as foreign.
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Immediate allergic responses, usually consisting of cold-like symptoms, are due to the activity of antibodies. Delayed allergic responses such as contact dermatitis, are due to the activity of T cells. Tissue rejection occurs when the immune system recognizes a tissue as foreign.
When a person has an autoimmune disease, cytotoxic T cells or antibodies mistakenly attack the body's own cells as if they bear foreign antigens. There are no cures for autoimmune disorders, but sometimes immunosuppressive drugs are effective. Some disorders of the immune system are:
- Myasthenia gravis-antibodies attach to an interfere with functioning of neuromuscular junctions and muscular weakness results
- Multiple Sclerosis-T cells attack the myelin sheath of nerve fibers which causes neuromuscular symptoms
- Systemic Lupus Erythematosus-various symptoms prior to death due to kidney damage
- Rheumatoid Arthritis-affected joints with severe pain
http://medicineworld.org/images/blogs/6-2007/rheumatoid-arthritis-17890.jpgAIDS
Acquired immunodeficiency syndrome (AIDS) is caused by the human immunodefiency virus (HIV.) There are 2 types of HIV: HIV-1 and HIV-2. HIV-1 is the more virulent and widespread form of HIV. AIDS originated in Africa and spread to the US and Europe by way of the Carribean. Both HIV-1 and HIV-2 correspond with types of viruses found in primates in Africa. The virus may have mutated after humans ate nonhuman primates for meat. AIDS is a pandemic because the disease is prevalent in the entire human population around the globe.
http://newsimg.bbc.co.uk/media/images/41703000/gif/_41703244_2006_figures4_416.gifHIV infection has different phases:
- Category A: Acute Phase-no apparent symptoms, highly infectious, and has a CD4 T cell count that has never fallen below 500 cells per mm cubed.
- Category B: Chronic Phase-CD4 T cell count between 499 and 200 cells per mm cubed and a variety of symptoms related to an impaired immune system: yeast infection, cervical dysplasia, prolonged diarrhea, thick sores on the tongue, or shingles, swollen lymph nodes, recurrent fevers, cough, or fatigue
- Category C: AIDS-CD4 T cell count below 200 cells per mm cubed or the person has developed one or more of the 25 AIDS defining illnesses. People with AIDS die from one or more of the the following opportunistic infections: pneumocystis jiroveci pneumonia, mycobacterium tuberculosis, toxoplasmic encephalitis, Kaposi's sarcoma, or invasive cervical cancer
http://biology.kenyon.edu/slonc/gene-web/Lentiviral/hiv_image.jpgHIV Life Cycle:
- Attachment
- Fusion
- Entry
- Reverse transcription
- Integration
- Biosynthesis and cleavage
- Assembly
- Budding
http://www.tthhivclinic.com/fig_3.gif
HIV testing does not test for the virus itself, but for the presence of HIV antibodies in the body. Most people develop antibodies to HIV within 2-8 weeks, but it can take up to 6 months. HIV and AIDS do not have a cure, but a treatment called highly active antiretroviral therapy (HAART) is usually able to stop HIV replication to such an extent that the viral load becomes undetectable. Vaccines are not yet available for HIV, but testing continues.
Citations:
Blood, Molecules, and Diseases. (2008) http://www.sciencedirect.com/science/journal/10799796
CDC, HIV Transmission. (2008) http://www.cdc.gov/hiv/resources/factsheets/transmission.htm
Heart Information System. (2008) http://www.texasheartinstitute.org/HIC/Anatomy/
Mader, S. (2008) Cardiovascular System: Heart and Blood Vessels, Cardiovascular System: Blood, Lymphatic System and Immunity, AIDS Supplement. Human Biology, 10th ed. (p 85-142,343-352)
Microbiology. (2008) http://www.scienceprofonline.org/
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