I have divided the first major topic for unit II into six subtopics. Each subtopic is handled separately. This review is organized in the following format: subtopic outline, discussion of the subtopic, and finally references for that subtopic.
Subtopics Discussed in this Review:
I. Cardiovascular System: The Heart and Blood Vessels
II. Cardiovascular System: The Blood
III. Microbes and Pathogens
IV. The Lymphatic System
V. Immunity and Immune Disorders
VI. HIV and AIDS
Subtopic I - The Cardiovascular System: The Heart and the Blood Vessels 
Outline
- Structure of the Cardiovascular System
- Regulation of the Heart Beat
- Pattern of Blood Flow Through the Heart
- Pulmonary and Systemic Circuits
- Capillary Exchange
- Evaluating Cardiovascular Function
- Cardiovascular Disease and Disorders
http://www.abc.net.au/science/articles/2008/01/14/2137790.htm
Discussion 1.1 The Structure of the Cardiovascular System
Structure of the Heart
The primary purpose of the cardiovascular system is to deliver materials to the cells and transport wastes away from the cells. The cardiovascular system is composed of the heart and the blood vessels. In addition, the respiratory system and the lymphatic system work closely with the cardiovascular system to achieve this goal.
The primary organ of the cardiovascular system is the heart. The major structure of the heart is a muscle called the myocardium which is composed of branched muscle fibers that are connected to each other by intercalated disks. The myocardium is surrounded a membrane called the pericardium. The pericardium is actually a double layered membrane that forms a sac around the heart muscle. Its outer layer (the fibrous pericardium) serves to protect and support the heart. A portion of the inner (serous pericardium) produces pericardial fluid that lubricates the heart and allows the pericardium to slide over the heart as it beats. (1) http://en.wikipedia.org/wiki/Pericardium
The heart muscle is not nourished by the blood that is contained within its chambers. The coronary arteries are responsible for providing oxygen and other needed materials to the cells of the heart. The coronary arteries are found above the aortic semilunar valve and run along the outside of the heart muscle. The coronary arteries then branch into arterioles and then into capillary beds. The capillary beds then merge into venules and finally into cardiac veins that return O2 poor blood to the right atrium. The image to the right is a view of the outside heart structure that details the coronary arteries and cardiac veins.
(Image right) http://my.clevelandclinic.org/heart/disorders/cad/cad_arteries.aspx
The aorta and the pulmonary artery are the major arteries that come out of the heart. The pulmonary artery takes blood from the heart to the lungs and the aorta takes blood from the heart to the body. There are also two major veins that come into the heart. They are the superior and inferior vena cava which bring O2 poor blood from the body back to the heart.
The inside of the myocardium is composed of four chambers. The right and left sides of the heart are separated by a thin wall called the septum. The upper two chambers of the heart are the right and left atria and the lower two chambers are the right and left ventricles. The atria and the ventricles are separated by the atrioventricular valves. These valves prevent the blood from flowing the wrong direction in the heart.
The atrioventricular valve that is found between the right atrium and the right ventricle is known as the tricuspid valve. The atrioventricular valve on the left is the bicuspid valve. The bicuspid and tricuspid valves are anchored to pappillary muscles found along the wall of the ventricles by fibrous protrusions called chordae tendineae. This support system composed of the pappillary muscles and the chordae tendinaeae is called the subvalvular apparatus. (2)http://en.wikipedia.org/wiki/Heart_valve . Two other valves called the semilunar valves are also present in the heart. The pulmonary semilunar valve is found between the right ventricle and the trunk of the pulmonary artery. The aortic semilunar valve is found between the left atrium and the aorta.
The images and text below summarize the structure of the heart. 
Structure of the Blood Vessels
There are three types of blood vessels. They are arteries, capillaries, and veins. Arteries and veins are composed of the same three layers. The layers are (from the outside in) connective tissue, smooth muscle with elastic tissue, and then endothelium which is a very thin layer of cells. Eventhough, arteries and veins have the same basic structure, there are differences based on their function. For example, arterioles are very small arteries that are surrounded by primarily smooth muscle. The smooth muscle can constrict or dilate the arteriole by either contracting or relaxing. (This plays a part in blood pressure and will discussed further in a moment). Also, the walls of veins and the smaller venules have less connective tissue and less smooth muscle than arteries. Because of this the veins serve as a holding area for much of the body's blood (up to 70%).
Capillaries are the third type of blood vessel and are the smallest. The wall of capillaries is made up of only endothelium attached to a basement membrane. The arterioles flow into the capillaries and the capillaries form dense beds (capillary beds) that are found throughout the body. Capillaries are the site of the exchange of materials from the blood to the tissue fluid (this will discussed in a later section of this review). The capillaries are able to open and close depending on the need of the tissue they are associated with. This is accomplished by the precapillary sphincter contracting. When this happens the blood is moved from the arteriole directly to the venule through the arteriovenous shunt.
The image to the right illustrates the structure of arteries, veins, and capillaries as well as the capillary bed.
Discussion 1.2 Regulation of the Heart Beat
Intrinsic Conduction System of the Heart
The heart "beat" is what sends blood from the heart through the body. Each heartbeat is a cardiac cycle. During each cycle the atria contract followed by the ventricles. This period when the heart muscle is contracting is called systole. After systole is diastole, when the heart muscle is relaxed and no chambers are contracted. The number of heartbeats per minute varies from person to person and also by activity, but on average the human heart beats 70 times per minute at rest. The characteristic sound of the heart beating "lub - dub" is casued by the AV valves closing. First the tricuspid valve and then the bic
uspid valve.
The contractions of the myocardium that create the heartbeat are initiated by special regions of the heart called nodal tissue. Nodal tissue is specialized in such a way that it behaves like muscle tissue and nervous tissue. There are two separate regions of nodal tissue. The first is called the sinoatrial node (SA node). The SA node is located in the upper portion of the right atrium. The SA node is called the "pacemaker" of the heart because its function is to regulate the heart beat. Every 0.85 seconds the SA node creates an impulse that causes the atria to contract. This impulse travels to the atrioventricular node (AV node) located in the lower portion of the right atrium near the septum. When he AV node receives the signal from the SA node it pauses briefly to allow the atria to complete their contractions, and then creates an impulse that moves through the branches of the atrioventricular bundle to the purkinje fibers in the bottom of the ventricles. This impulse causes the ventricles to contract. (Right)
Extrinsic Regulation of the Heartbeat
The heart beat is also controlled by a portion of the brain called the medulla oblongata through the function of the parasympathetic and sympathetic nervous systems. The parasympathetic nervous system controls the function of the body when it is at rest and causes the SA and AV node activity to be slowed. The sympathetic nervous system controls the bodies "fight or flight" mechanism and stimulates the SA and AV node activity.
Another way the brain controls the heart rate is through the release of hormones. Epinephrine and norepinephrine are two hormones released by the adrenal medulla that cause the heart rate to increase.
Discussion 1.3 Path of Blood Flow Through the Heart
Before blood can be pumped to the cells, the heart first pumps the blood to the lungs so that it can carry oxygen to the cells. This is why the heart is called a "double pump". The right side of the heart is responsible for getting blood to the lungs, while the left side is responsible for getting blood to the body. The image below illustrates the pattern that blood takes as it travels through the heart.
Path of Blood Through the Heart
(Blue Lines = O2 Poor Blood Red Lines = O2 Rich Blood)
- Superior & Inferior Vena Cava (blood from body)
- Right Atrium
- Tricuspid Valve
- Right Ventricle
- Pulmonary Semilunar Valve
- Pulmonary Trunk
- Right & Left Pulmonary Artery (To Lungs)
- (From Lungs) Right & Left Pulmonary Veins
- Left Atrium
- Bicuspid Valve
- Left Ventricle
- Aortic Semilunar Valve (not pictured)
- Aorta (To Body)
Discussion 1.4 The Path of Blood Flow Through the Body
Once the pulmonary arteries leave the heart, they branch into arterioles that carry blood into the capillaries of the lungs. In the capillaries carbon dioxide is exchanged for oxygen. The blood flows slowly through the capillaries (due to decreased blood pressure) which facilitates this exchange. The blood then moves into the pulmonary venules and then the four pulmonary veins before reentering the heart.
Systemic Circuit
The systemic circuit is the system of circulation that delivers the blood to all the tissues and structures of the body. Oxygenated blood leaves the aorta and flows through a network of arteries, arterioles, and capillaries in order to bring oxygen and nutrients to all the tissues of the body. As the blood flows through the capillary beds of the body it also takes up wastes that the cells have released into the tissue fluid.
The capillaries flow into venules and the venules flow into veins. The blood is moved through the veins not by the pumping of the heart but by contractions of the skeletal muscles (skeletal muscle pump) and the function of the respiratory pump. The respiratory pump is simply the change in pressure created between the thoracic and abdominal cavities when we breath. The blood moves from higher pressure to lower pressure. The presence of valves in the veins prevents blood from flowing backward when the blood is being moved against gravity.
Portal Systems
Most of the time the blood follows the pattern described above, sometimes however there are connections from one capillary bed to the next. An example of this is the hepatic portal system which is composed of the hepatic portal vein that takes blood between the capillary bed of the digestive system to the capillary bed of the liver. This system delivers glucose and amino acids that the digestive system receives from food to the liver. The liver stores glucose in the form of glycogen and uses amino acids to build proteins. The liver also removes any pathogens that may have been taken into the body through the digestive process.
Discussion 1.5 Exchange at the Capillaries
The image below illustrates how nutrients and oxygen leave the thin walls of the capillaries and move into the tissue fluid where it can be taken into the cells of the body. This exchange is facilitated by osmotic pressure and blood pressure. At the end of the capillary closest to the artery the blood pressure inside is higher than the osmotic pressure outside in the tissue fluid, thus water leaves the capillary. At the venous end of the capillary the situation is reversed. The blood pressure is lower than the osmotic pressure water enters the capillary. In the middle of the capillary bed where osmotic pressure and blood pressure are the same, materials are able to diffuse along their normal concentration gradient. Oxygen and nutrients leave the capillary while carbon dioxide and waste material enter the capillary.
Discussion 1.6 Evaluating Cardiovascular Function
Electrocardiogram
One of the ways physicians monitor the heart beat is through an electrocardiogram (ECG). This is done by putting electrodes on the surface of the skin. The electrodes are connected to wires that carries the impulses to a recording device that notes the function of the heart with lines on a piece of paper. This is possible because the electrical changes in the myocardium create currents that the cells of the body a
re able to conduct (because the cells contain ions).
A normal ECG has the pattern of electrical waves indicated in the image to the right. The P Wave is created when the SA node causes electrical changes in the fibers of the atria. The P wave is a sign that the atria are about to contract. The Q, R, and S, waves together occur just before the ventricle contracts and show that the AV node has signaled the ventricle to contract. After the ventricles contract the T-wave occurs which indicate that the fibers of the ventricles are in recovery.
Taking the Pulse
Another way the heartbeat is monitored is by taking the pulse. The pulse (which mirrors the beating of the heart) can be easily felt in the inside of the wrist (radial artery) or the in the neck (carotid artery). The pulse is created by the arterial wall expanding and recoiling as blood is pumped through it by the heart.
Another useful measure in evaluating the function of the heart is blood pressure. The blood pressure refers to the amount of pressure the blood exerts on the arteries. Blood pressure is measured at the brachial artery of the arm by an instrument called the sphygmomanometer. When blood pumps out of the heart the pressure in the arteries increases. This is the systolic pressure. When the ventricles are relaxed blood pressure in the arteries is reduces. This is the diastolic pressure. Normal blood pressure is 120/ 80 mmHG (millimeters of mercury). The top number refers to the systolic pressure (highest pressure reached in the artery). The bottom number is the diastolic pressure or the lowest pressure reached in the artery. The blood pressure is the highest in the aorta and lowest in the venules and veins. What happens when the pressure is too low or too high will be discussed later.
Discussion 1.7 Cardiovascular Disease and Disorders
Diseases of the cardiovascular system are very serious and are the leading cause of early death in U.S. and also represents the most costly of diseases on the American health care system. Cardiovascular disorders can affect the blood vessels and the heart muscle itself. There are a number of diseases and conditions that are characterized as cardiovascular disease. These conditions are listed below. (3) http://www.mayoclinic.com/health/cardiovascular-disease/HB00032
Just like we saw in the previous unit on cancer, a number of cardiovascular diseases are due to lifestyle choices such as diet, physical activity, smoking, and alcohol consumption and can be prevented. In some cases there are genetic influences at work and an individual's only risk factor is a familial history of cardiovascular problems. Below is a discussion of some common conditions related to the cardiovascular system.
HypertensionHypertension (also known as high blood pressure) is when the blood is pumped out of the aorta under greater pressure than normal. As mentioned above, the normal blood pressure for an adult is 120/ 80 mmHg. An individual is considered to have hypertension when their blood pressure is over 140/ 90 mmHg. A number of conditions can develop as a result of hypertension or often appear in tandem with hypertension. Hypertension can be treated with medication but can often be prevented entirely through healthy lifestyle choices.
If there is a weak point in a vessel increased blood pressure can cause the vessel to burst (aneurysm). Aneurysms typically occur in the abdominal artery or in the arteries that go into the brain. If an aneurysm is caught early enough, the damaged vessel can be replaced.
Atherosclerosis occurs when plaque deposits build up in the blood vessels. If these deposits block a vessel and interrupt blood flow they can cause a stroke or heart attack (myocardial infarction) depending on their location. The image to the right illustrates what happens when plaque builds up on the arterial wall. In addition to hypertension, artherosclerosis can be caused by a diet high in saturated fat, smoking, and also bacterial or viral infections. Artherosclerosis typically begins to develop in early adulthood but symptoms typically don't appear until midlife.
Plaque in the arterial walls can cause a blood clot to form in an artery (thrombus). If this clot breaks loose (embolus), it can travel through the blood system and block the small arteries of the heart or brain. Again, this can lead to a heart attack or a stroke. If an artery that feeds the heart muscle is partially blocked the resulting pain down the left side of the body is called angina pectoris. This type of blockage can be treated with medication to dilate the artery and dislodge the clot or the clot can be dissolved through a drug that causes the body to produce a clot dissolving enzyme.
If the artery is completely blocked a heart attack results and will require treatment if the damage to the heart muscle is not severe enough to cause death initially. Depending on the location of the clogged artery the individual may require bypass surgery, angioplasty, or a stint to regain normal blood flow to the heart muscle. Other treatments being explored are using gene therapy to grow new vessels in the portion of the heart where the blood flow is lessened.
Heart Failure
Heart transplant is a last resort treatment used when the heart is too damaged to be repaired by other means. New technologies are being explored to replace human to human transplants. These include implanting a device that assists the left side of the heart in its pumping (LVAD -left ventricle assistance device), transplanting organs of genetically engineered animals, and implanting full mechanical pumps in place of the heart. 
References
Image References
Images obtained from Aris site for Human Biology by Sylvia Mader (http://highered.mcgraw-hill.com/classware/selfstudy.do?isbn=0072986867 chapter resources - power point presentation), unless otherwise cited under image.
Topic References
(1) http://en.wikipedia.org/wiki/Pericardium. (2) http://en.wikipedia.org/wiki/Heart_valve (3) http://www.mayoclinic.com/health/cardiovascular-disease/HB00032. All additional information for this subtopic obtained from Human Biology; Mader, Sylvia S., and instructor power point presentation.
Subtopic II- The Cardiovascular System: The Blood
Outline
- Composition and Function of Blood
- Red Blood Cells and Gas Exchange
- White Blood Cells and the Body's Defense System
- Platelets and Blood Clotting
- Blood Types
- Diseases and Disorders of the Blood
- Body System Interdependence
http://static.howstuffworks.com/gif/artificial-blood-1.jpg
Discussion 2.1 Composition and Function of the Blood
As discussed in the previous unit, the blood is actually considered fluid tissue. The blood is made up of two different types of cells (red blood cells and white blood cells) and cell fragments called platelets. These formed elements are surrounded by a liquid matrix (plasma).
The blood plays a major role in maintaining homeostasis by helping to regulate body temperature and also by regulating the body's water-salt ratio. This is accomplished by the plasma. Plasma is primarily composed of water, but also contains a small amount of ions and organic molecules. The ions help to regulated the fluid balance in the blood. The plasma carries organic molecules like glucose that provides nourishment to the cells, wastes like urea produced by the kidney's , but also the plasma carries proteins.
There are three kinds of plasma proteins. They are albumins which are produced by the liver and help to transport other substances through the body by binding with them. Globulins are a plasma proteins that are produced by the white blood cells and also aid in transport. The final plasma protein is fibrinogen. Fibrinogen is produced by the liver and helps the platelets in the formation of blood clots.
Discussion 2.2 Red Blood Cells and Gas Exchange 
Red blood cells are the most abundant of the blood's cells. Red blood cells (RBC) primarily contain numerous hemoglobin molecules. RBC lack many of the organelles common to other cells of the body including the nucleus and mitochondria. Because RBC lack a nucleus (lost during maturation) they have a biconcave shape that increases the surface area of the cell available for transporting O2 and CO2. RBC's use anaerobic respiration to produce energy for the cell and thus do not use any of the oxygen that they transport. RBC are formed from stem cells that are found in the bone marrow. RBC only live about 120 days. After that they are broken down by white blood cells in the spleen. The amino acids that compose the polypeptide chains of hemoglobin (discussed below) are recycled, the iron is reused by the bone marrow, and the rest of the RBC is broken down and excreted by the liver.
Each hemoglobin molecule of the RBC is composed of four polypeptide chains wrapped around an iron containing heme group. The iron in the heme group bonds loosely to oxygen when the blood flows through the capillaries of the lungs. When this happens the hemoglobin changes shape and becomes oxyhemoglobin. There are four heme groups in each hemoglobin molecule (each carries and O2 molecule).
Once the RBC reaches the tissues the oxygen is released and the hemoglobin molecule again changes shape and is now called deoxyhemoglobin. The hemoglobin is now free to transport CO2. About 25% of the CO2 in the cells is transported directly by the hemoglobin molecules of the red blood cells. This is possible because the CO2 molecule bonds to the amino groups at the end of the globin molecules. A small portion of the CO2 produced by the cells simply diffuses into the plasma, the remaining CO2 is converted into bicarbonate (HCO3-) and is also transported by the plasma back to the lungs. The reaction below illustrates how bicarbonate is produced. The H+ ion that result from the production of bicarbonate are also taken up by the globin molecules. This allows the blood to not only transport CO2 out of the cells but also to h
elp maintain the pH balance of the body.
Discussion 2.3 White Blood Cells and the Body's Defense System
White blood cells can be distinguished from red blood cells in several ways. White blood cells are larger, contain a nucleus, and are much less numerous than red blood cells. They are produced by the red bone marrow from stem cells at the direction of the protein CSF or colony stimulating hormone. There are several different types of white blood cells, each type is specialized for a different function in the body. There are two categories of white blood cells (or leukocytes), they are grandular leukocytes and agrandular leukocytes. The different types of white blood cells and their functions are outlined in the table below.
| Grandular Leukocytes | Function | Appearance |
| Neutrophils | Most Abundant WBC Multilobed Nucleus (Polymoponuclear) First WBC to Attack Invading Bacteria Cause of Pus (When Destroyed)
| |
| Eosinophils | Bilobed Nucleus Function Not Well Known Increase in Presence of Parasites and Allergens
| |
| Basophils | U-shaped Nucleus Release Histamine During Allergic Reaction
|
| Agrandular Leukocytes | Function | Appearance |
| Lymphocytes | 2nd Most Abundant WBC Recognize and Cause Immunity to Certain Antigens Two Kinds of Lymphocytes (T Cells & B Cells) T Cells Kill Invaders Directly B Cells Produce Antibodies
|
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| Monocytes | Largest of the Blood Cells Reside in the Tissues Group Together to Form Macrophages In Skin Become Dendrytic Cells Perform Phagocytosis of Old Cells Alerts Lymphocytes to Threats to Body |
|
Discussion 2.4 Platelets and Blood Clotting
Blood platelets are not cells but rather fragments of cells called megakaryocytes that originate in the red bone marrow. Platelets, plasma proteins (thrombin and fibrinogen), calcium ions, and numerous other clotting factors all work together to form a blood clot when a vessels is punctured.
- Initially, platelets respond to an injury and attempt to seal the wound. Sometimes this is all that is necessary to stop the bleeding. If a wound is too large the platelets produce prothrombin activator.
- Prothrombin actitivator that was produced by the platelets turns the plasma protein prothrombin into thrombin.
- Thrombin then cuts fibrinogen molecules (which are short) in half. The fragmented fibrinogen links together to create long strings of fibrin.
- The fibirin strings get wrapped around the platelets and together they close the break in the vessel. Red blood cells also get caught up in the threads.
- Once the body begins to repair the break in the vessel, the clot is broken up by the enzyme plasmin.
Discussion 2.5 Blood Types
The red blood cells of all individuals are not the same. Red blood cells have identifying proteins on their plasma membranes (glycoprotiens) and these proteins vary between individuals. Blood type is the categorization of blood based on these glycoproteins. There are two major categories used to describe blood type. These are the ABO blood group and the Rh Blood Group. The image to the right illustrates the different ABO blood groups.
Knowing a persons Blood type is of utmost importance when doing 
blood transfusions. This is because the plasma has antibodies that recognize and destroy any blood cells that do not have the same glycoproteins as the individuals blood (agglutination). Antibodies to "foreign" blood develops in infancy.
This means that donor blood must be compatible with an individuals blood before they can receive a blood transfusion. The chart below illustrates the compatibility of ABO blood types for blood transfusion.
| Blood Type | Possible Donors |
| A | O or A |
| B | O or B |
| AB | O, A, B, or AB |
| O | O |
You'll notice that individuals with AB blood can receive all blood types (universal recipient). Individuals with O blood can only receive O blood but can donate blood to all blood types. For this reason O is known as the universal donor. This table is just a generalization because other variations in blood type do exist.
There are only two Rh groups. Blood either has the Rh factor (Rh+) or it does not (Rh-). Unlike the ABO antibodies, Rh antibodies do not already exist in the plasma of those who are Rh-. They develop if a person is exposed to Rh+ blood. To avoid compatibility problems due to Rh factor blood typing also includes evaluation of the Rh as well as the ABO blood types. One situation where this does pose a problem is during pregnancy and childbirth if the mother's and the baby's blood mixes. If a mother is Rh- and her baby is Rh+ the mother's blood may form antibodies to the Rh factor and attack the baby's blood. This is usually not a problem unless the mother has another Rh+ baby because it time for the antibodies to form. The resulting condition in the baby is called hemolytic disease of the newborn.
Discussion 2.6 Diseases and Disorders of the Blood
| Disorders of the Red Blood Cells | |
| Iron Deficiency Anemia | Anemia caused by iron deficiency |
| Pernicuious Anemia | Anemia caused by lack of B12 |
| Folic Acid Deficiency Anemia | Anemia caused by a lack of folic acid (especially impacts pregnant women and can cause birth defects) |
| Hemolytic Anemia | RBC’s rupture leading to anemia |
| Sickle Cell Disease | RBC are abnormally shaped due to inherited genetic disorder. Leads to RBC rupturing in the capillaries. Life span of RBC reduced to about 90 days. Causes early death. |
| Hemolytic Disease of the Newborn | Caused by Rh incompatibility. Causes severe anemia in newborn. |
| Disorders of the White Blood Cells | |
| SCID (Severe Combined Immunodeficiency Disease) | Stem cells of the WBC lack the enzyme adenosine deaminase. The body isn’t able to fight infections at all. It is treated with gene therapy or repeated replacement of the enzymes through injection. |
| Leukemia | Type of cancers where the WBC are abnormal or immature. These abnormal WBC cannot defend the body leading to repeated and life threatening infections. |
| Epstein Barr Virus | Virus that causes infectious mononucleosis. It is an infection of the leukocytes. Most common human virus. |
| Disorders of the Platelets and Blood Clotting | |
| Thrombocytopenia | Not enough platelets either because the marrow isn’t producing enough or because they are being destroyed after being produced. Leads to easy bruising, nosebleeds, and other bleeding. Can be serious if bleeding occurs in brain or intestines. |
| Thromboembolism | Clot caused by plaque in vessel that breaks away from vessel wall. Can lead to heart attack or stroke. |
| Hemophilia | An inherited disorder where the body lacks certain clotting factors. Leads to uncontrolled bleeding. |
Discussion 2.7 Body System Interdependence
All of the systems of the body work together to maintain homeostasis. For example, the heart and cardiovascular system alone can not keep the body alive. The respiratory system must perform its job to bring oxygen into the lungs for the blood to deliver to the cells. The digestive system must breakdown the food we eat so that the blood can deliver nutrients to the cells. The image below illustrates how all the other systems of the body work together to accomplish the basic goal of the cardiovascular system which is to transport oxygen, nutrients, and wastes to and from the cells of the body.
References
Image References
Images obtained from Aris site for Human Biology by Sylvia Mader (http://highered.mcgraw-hill.com/classware/selfstudy.do?isbn=0072986867 chapter resources - power point presentation), unless otherwise cited under image. 
Subtopic III - Microbes and Pathogens
Outline
- Kinds of Microbes
- Bacteria
- Viruses
- Prions
(Image left) http://www.nextnature.net/?p=1785
Discussion 3.1 The Relationship of Microbes and Humans
Microbes
Microbes are tiny organisms and include bacteria, viruses, and prions. Microbes are found every where and on everything, including inside the human body. Some microbes are helpful to humans and the environment while others are harmful and cause disease. Some examples of how microbes can be helpful is in producing foods such as yogurt, producing medications, and in decomposing plant and biological wastes.
Bacteria
Bacteria are prokaryotic and lack a nucleus. There are three primary types of bacteria that occur in different shapes: Bacillus (rod shaped), Coccus (spherical shaped), Spirillum (curved shaped). All bacteria contain a cell wall that is made out amino-disaccharide chains. The cillin class of anitbiotics functions by preventing bacteria from creating this amino-disaccharide cell wall. Bacteria reproduce very rapidly via binary fission.
The table below illustrates some of the ways that bacteria can be specialized.
| Can be encapsulated which causes them to be sticky and adhere to surfaces and be protected against phagocytes. |
| Can move through the use of flagella. |
| Can have fimbria which are fibers that let bacteria cling to surfaces. |
| Can have a tube like appendage called a pilus that the bacteria uses to transfer DNA from one cell to another (like antibody resistant genes). |
| Can have a secondary ring of DNA called a plasmid. |
Viruses
Viruses are very tiny (100 times smaller than a eukaryotic cell) parasitic organisms that are not able to live outside the body of a host. They are acellular and typically use the host ribosomes and enzymes to reproduce. They are typically composed of two parts. They have an outer capsid made of proteins and an inner core with nucleic acids. Viruses can mutate and change frequently making them difficult to vaccinate against. 
Prions
Prions are specialized proteins found in the brain and nerve tissue. Sometimes these proteins spontaneously change shape thus becoming unable to function. Prions have the ability to cause other (healthy) prions to change shape as well. These denatured proteins cause Creutzfeldt-Jacobs Disease.
References
Image References
Images obtained from Aris site for Human Biology by Sylvia Mader (http://highered.mcgraw-hill.com/classware/selfstudy.do?isbn=0072986867 chapter resources - power point presentation), unless otherwise cited under image.
Subtopic IV - The Lymphatic System
Outline
- Functions of the Lymphatic System
- Lymphatic Vessels
- Organs of the Lymphatic Organs
(Image Left) http://www.loftinhealth.com/lymphaticdrainage.html
Discussion 4.1 Functions of the Lymphatic System
The lymphatic system (discussed in Unit I review as well) is composed of the lymphatic vessels and lymphatic organs. The lymphatic vessels carry the tissue fluid lymph throughout the body. There are four primary functions of the lymphatic system 1) Absorption of excess tissue fluid by the lymphatic capillaries 2) Fat absorption in the small intestines, 3) Produce, maintain, and distribute lymphocytes, 4) Fight pathogens that enter the body.
Discussion 4.2 The Lymphatic Vessels
The lymphatic vessel network is made up of lymphatic capillaries, lymphatic veins, lymphatic ducts. The capillaries take up excess tissue fluid. Fluid moves through the lymphatic capillaries because of skeletal muscle contractions. Next the lymphatic fluid or lymph moves into lymphatic veins that are very similar to the veins of the cardiovascular system. There are valves in the lymphatic veins that keep the fluid moving in the right direction. Finally, the lymphatic veins end in two ducts. The thoracic duct returns lymph to the left subclavian vein and the right lymphatic duct returns lymph to the right subclavian vein.
Discussion 4.3 Lymphatic Organs
There are two types of lymphatic organs: primary and secondary organs. Primary lymphatic organs are the red bone marrow and the thymus gland. The secondary lymphatic organs are the spleen, lymph nodes, lymph nodules, the appendix, and Peyer's patches. I have listed the lymphatic organs as well as their functions below.
| Organ | Function |
|
| Red Bone Marrow | The red bone marrow is found in the sternum, vertebrae, ribs, pelvic girdle, and end of the humorous and femur of adults. (Most bones of children contain red bone marrow). Red bone marrow is responsible for blood cell production including red blood cells, neutrophils, eosinophils, basophils, lymphocytes, and monocytes. In addition, B cells mature in the red bone marrow. |
|
| Thymus Gland | The thymus is a gland found between the trachea and the sternum. T cells mature in the thymus and the thymus is responsible for the production of thymic hormones that also help to mature T cells. |
|
| Spleen | The spleen is the largest of the lymphatic organs and is located in the upper left quadrant of the abdominal cavity. The spleen is responsible for filtering the blood. The spleen is divided into two different regions; the red pulp and the white pulp. The red pulp is a region that contains macrophages remove old red blood cells. The white pulp contains many T cells and B cells that help cleanse the blood of pathogens. (1) http://en.wikipedia.org/wiki/Spleen |
|
| Lymph Nodes | Lymph nodes are found along the lymphatic vessels throughout the body. They are divided into sections and each section contains a sinus. As the blood goes through the sinuses macrophages filter our pathogens. The lymph nodes also contain lymphocytes to further defend the body against infection and disease. |
|
| Lymphatic Nodules | Lymphatic nodules are similar to lymph nodes but they are not surrounded by a connective tissue capsule like lymph nodes. The tonsils are an example of lymphatic nodules. The function of lymphatic nodules is the same as lymph nodes. |
|
| Peyer’s Patch |
Peyer’s patches are lymph tissue found along the intestines that dispose of pathogens that enter the digestive tract. (image right) http://embryology.med.unsw.edu.au/histology/git/peyer_patch_he.jpg |
|
| Appendix |
The appendix is found attached to the cecum and is a pouch of tissue that also helps serves to filter pathogens from the digestive tract.
(image right) http://ibs.about.com/b/2007/11/02/is-the-appendix-important.htm |
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Subtopic V - Immunity
Outline
- Nonspecific Defenses and Specific Defense
- Cell Mediated Immunity
- Antibody Mediated Immunity
- Antibodies: Structure and Function
- Acquired Immunity
- Hypersensitivity and Immune Disorders
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Discussion 5.1 Nonspecific Defenses of the Immune System
There are two levels of nonspecific defense the body uses to prevent infection by invading pathogens. They are barriers to entry and the inflammatory response.
1. Barriers that prevent pathogens from entering the body.
The skin and mucous membranes are the first parts of the body that pathogens come in contact with. They are designed to prevent pathogens from entering beyond this outer epithelial layer. On the skin's surface there are chemical barriers as well. The sebaceous glands produce sebum that contains special chemicals that kill bacteria on the skin before it can make it's way into the body. There are also lysosomes excreted in sweat and tears that kill pathogens. In addition to forming a protective barrier the respiratory tract contains ciliated cells that function to push debris and pathogens back out of the body. The digestive tract utilizes lysosomes in the saliva as well as stomach acid to kill bacteria. In addition to these, the body houses "good" bacteria that are not harmful to us but prevent harmful bacteria from having a sustainable environment to live in by using up available nutrients.
2. The inflammatory response that occurs if a pathogen does enter the body.
If a pathogen does manage to get past the barriers mentioned above the body will often mount an inflammatory response. The inflammatory response begins when damaged tissues release histamine. Histamine is a protein that causes the capillaries to dilate. This brings more blood to the area which will bring more white blood cells (neutrophils and macrophages) to the area to perform phagocytosis. In addition, increased blood flow causes the temperature of the area to rise. This may inhibit the growth of the pathogen. These events are responsbile for the characteristics of inflammation (redness, swelling, pain, warmth). If the inflammatory response is not successful in controlling the pathogen the neutrophils will release cytokines which stimulate the body's more specific defenses against infection (which will be discussed in a moment). If the body is damaged in some way such as a cut or a sprain, the inflammatory response also assists in the formation of blood clots as well as preventing infection.
Complement System
The complement system is made up of specialized proteins that assist in immune responses. The inflammatory response is sometimes helped in it's effort to control infection and kill pathogens by the complement system. The actions of the complement system are outline below.
- Stimulate histamine production.
- Signal for phagocytes to an area with pathogens.
- Attach to pathogens to make sure they are phagocytized by the WBC.
- Create a membrane attack complex that can poke holes in the cell membrane of pathogens causing lysis.
- Proteins called interferons are produced by virus infected cells that cause noninfected cells to boost their defenses.
Specific Defenses - Overview
The body's specific immune defenses involve the action of the B cells and T cells (lymphocytes). The chart below illustrates the way that B cells and T cells are further specialized. The surface of T cells and B cells contain antigen receptors that are capable of recognizing and binding to antigens that find their way into the body. The shape of the antigen receptors on T cells and B cells are specific to the particular antigen they were created to recognize. This means that there are literally millions of different variations of T cells and B cells in the body because we are exposed to such a vast number of antigens.
Discussion 5.2 Cell Mediated Immunity and T-Cells
http://en.wikipedia.org/wiki/T_cell
T cells are a type of lymphocyte (WBC) that matures in and is released by the thymus. They are responsible for attacking diseased cells. T cells have specialized receptor sites on their surface that correspond to a particular antigen (TCR); however, T cells are not able to recognize their corresponding antigen by themselves.
The response of T cells begins when an antigen-presenting cell (APC) like a macrophage or dendritic cell presents the antigen to the T cell. The APC partially digests the pathogen through phagocytosis and then a portion of the antigen is bound to the major histocompatibility complex (MHC) on the surface of the APC. MHC are proteins that are found on all the cells of all vertebrates that either display "self" proteins or when a pathogen is present they also display pathogen proteins. (1) http://genome.wellcome.ac.uk/doc_WTD020754.html. When the MHC is displaying the human proteins it is called the HLA (human leukocyte antigen). This MHC (with a portion of the antigen) presents itself to the T cell and the T cell is able to do a side by side comparison of the pathogen containing MHC and the HLA or "self" MHC. This how the T-cell recognizes "self" and "non-self".
After the antigen has been recognized as a foreign invader and the T-cell has been activated, clonal expansion occurs. Exactly which cells are created in clonal expansion are determined by which HLA complex presents the antigen.
If HLA I presents the antigen then the T cells will create cytotoxic T cells that seek and destory the pathogen. Cytotoxic T cells contain perforin molecules and enzymes called granzymes. Once the cytotoxic T cells locate a cell that contains a virus or a diseased cell they release the perforin molecules which perforate its cell membrane. The cytotoxic T cell then releases the granzymes into the infected or diseased cell which causes it to undergo apoptosis.
If HLA II presents the antigen then helper T cells will be produced that will be used to activate B cells by secreting cytokines.
After the virus is cleared most of the T cells undergo apoptosis themselves. A few T cells will remain which become memory T cells. Memory T cells remain to alert the body should a future infection of the same virus or disease occur.
Discussion 5.3 Antibody Mediated Immunity and B-Cells
As mentioned above, B cells are actived by cytokines that are excreted by helper T cells and each type of B cell has a receptor site (BCR) that corresponds to a particular antigen. This process is clonal selection. Once the B cell has been activated by cytokines and an antigen binds to the BCR the B cell duplicates itself in clonal expansion.
During clonal expansion most of the B cells that are produced will be plasma cells . These plasma cells differ from regular B cells in that they have more endoplasmic reticulum which produces antibodies. The antibodies produced will be identical to the BCR for the antigen being fought. (The action of antibodies will be discussed in the next discussion). Other B cells will be memory B cells that can recognize the antigen if an infection with the same pathogen occurs again some time in the future.
Like T cells, B cells that remain after an infection is cleared will undergo apoptosis (with the exception of memory B cells).
Discussi
on 5.4 Antibodies: Structure and Function
Antibodies are proteins that are produced by plasma cells in response to an antigen and are specific to the antigen they are fighting. Antigens are Y shaped. Each arm of the Y is made up of two polypeptide chains. One of these is longer than the other. The longer chain is known as the "heavy" chain and the shorter chain is known as the "light" chain. The ends of each arm of the Y contain antigen receptor sites and vary from one antibody to the next. The bottom or trunk of the antibody is constant among antibodies of the same class (below).
Antigens kill antibodies in three primary ways. 1)They can coat the antibody (neutralization). 2)They can attach to the pathogen drawing the attention of phagocytes. 3)As mentioned previously, antibodies also can activate the complement system.
There are five classes of antibodies. The chart below lists the different classes of antibodies and describes their location and functions in the body.
Discussion 5.4 Acquired Immunity
Active Immunity
Acquired immunity can be active or passive. Active immunity is when the body produces antibodies to a particular antigen as the result of exposure to that particular pathogen. This immunity is due to memory B cells and memory T cells. These memory cells remain after exposure to the pathogen and circulate through the body waiting for their particular antigen to reappear. If an individual is exposed to the antigen again the body will kill the pathogen before infection and illness can occur. This can happen in two ways. Either an individual can be exposed to a virus or other pathogen naturally or they may be intentionally exposed to an antigen through immunization.
Vaccines usually contain a small amount of a virus that has been inactivated so that it can't cause illness. New bio-technologies have made it possible to insert a single protein of a pathogen into a harmless bacteria. This bacteria is mass produced and serves as the vaccine. This is how the hepatitis B vaccine and vaccines again malaria are being created today.
Typically, vaccinations cause an initial immune response several days after vaccination. The body produces antibodies slowly and then a decline in antibodies occurs as the antigen is killed off. A second vaccination is usually done (called a booster) that causes the antibody level to rise much higher than the first time. At this point one is considered immune to the antigen. A blood test called an antibody titer can be done to test the plasma for the level of antibodies to a particular antigen.
Passive Immunity
Passive immunity is when antibodies are prepared in a lab and injected into an individual. Passive immunity also occurs when a mother's antibodies cross the placenta to the baby. Passive immunity is only temporary however. Infants immunity typically only lasts a few months or sometimes longer when a mother breast feeds (because some antibodies are delivered via breast milk). Another example of passive immunity is is when someone is given a gamma globulin injection to prevent illness after known exposure to a particular virus.
Discussion 5.5 Hypersensitivity and Immune Disorders
Allergies
Allergies occur when the the body's immune system is hypersensitive to something not normally considered an antigen. IgE antibodies are responsible for immediate allergic responses. Immediate allergic responses can be watery eyes and nose (as in hay fever), constriction of the airway (as in asthma), or nausea and intestinal symptoms (from food). If an allergen enters the blood stream anaphylactic shock can occur.
Another form of hypersensitivity is a delayed allergic response. This is caused by memory T cells. Some examples of delayed allergic response is skin rash (contact dermatitis) that occurs when the skin is exposed to an allergen.
Tissue Rejection
Just like the T cells recognize antibodies on the surface of HLA complexes as "not self" and try to destroy them, transplanted organs appear to the T cells to be foreign invaders. This is why tissue rejection occurs. Donor organs are carefully selected to be as closely matched to the recipient as possible. In addition, transplant recipients must take immunosuppressive drugs to prevent rejection. New avenues being explored to circumvent this problem are using transgenic organs from animals as well as growing human tissues in a lab that lack HLA antigens.
Autoimmune Disease
Sometimes cytotoxic T-cells ignore the designation as "self" on the HLA and attack the body's healthy cells. This leads to an autoimmune disease. The table below describes some common autoimmune disorders.
| Myasthenia Gravis | Antibodies attach to neuromuscular junctions and cause muscle weakness. |
| Multiple Sclerosis | T cells break down the myelin sheath that surround the nerves which causes a number of different neuromuscular problems. |
| Systemic Lupus Erythematosus (SLE) | Antigen-antibody complexes build up in the kidneys and causes kidney damage and eventually death. |
| Rheumatoid Arthritis | Recurrent inflammation of the joints draws T cells and B cells that deteriorate the joints. |
References
Image References
Images obtained from Aris site for Human Biology by Sylvia Mader (http://highered.mcgraw-hill.com/classware/selfstudy.do?isbn=0072986867 chapter resources - power point presentation), unless otherwise cited under image.
Topic References
(1) http://genome.wellcome.ac.uk/doc_WTD020754.html
Outline
- History and Origin of HIV
- HIV Life Cycle
- Stages of HIV Infection
- Transmission and Prevention
- HIV Testing and Treatment
(Image Right) http://www.bioquest.org/bedrock/images/hiv_nihal.jpg
Discussion 5.1 History and Origin of HIV
HIV has been traced back to Africa in the early 1950's. It is believed that the virus may have originated from an immunodeficiency virus found in certain kinds of monkeys in Africa and that it crossed over to humans when they ate the meat of infected animals. The earliest known case of AIDS in the United States was a 15 year old boy who died of Kaposi's sarcoma a cancer that is characteristic of those with AIDS (though at the time the cause of death was not known).
HIV is most prevalent in the Sub-Saharan Africa and Asia. Over sixty percent of all those infected with HIV live in these regions (24 million people). HIV infection is least prevalent in the Oceania region with only 16,000 infected in Australia in 2005.
The table below shows the Statistics for HIV infection around the globe in 2005.
Discussion 5.2 HIV Life Cycle
The image below illustrates the life cycle of the HIV virus
HIV Life Cycle
http://www.thebody.com/content/art6021.html
Discussion 5.3 Progression of HIV Infection
Infection with the HIV virus is characterized in three stages ending in the diagnosis of full blown AIDS.
| Category A: Acute Phase |
| Asymptomatic but very infectious period |
| T Cell count remains above 500 cells/ mm3 of blood |
| Immune system is still functioning as normal |
| High amount of replication of virus and increasing viral load |
| The body enters into a balancing act of T Cell production (producing nearly 2 billion per day) to keep up with the advancing viral replication and subsequent T cell death. |
| Category B: Chronic Phase |
| Symptoms of failing immune system: recurrent infections prolonged diarrhea, sores on tongue, singles, fevers, fatigue . . . |
| T Cell count remains between 499 and 200 cells/ mm3 of blood |
| High amount of replication of virus and increasing viral load |
| Category C: AIDS |
| Individual has one or more of the 25 AIDS associated diseases that include Pneumocystis jiroveci pneumonia, Mycobacterium TB, Toxoplasmic Encephalitis, Kaposi’s Sarcoma, Invasive Cervical Cancer |
| T Cell count is below 200 cells/ mm3 of blood |
| High amount of replication of virus and increasing viral load |
| Death typically occurs within 2 – 4 years of entering stage C |
Discussion 5.4 Transmission and Prevention of HIV/ AIDS
The HIV virus is transmitted person to person through intimate contact. The virus can be transmitted through blood, semen, vaginal fluid, and breast milk. Prevention of transmission is dependant on the practice of safe sex with the following recommendations: abstinence, sex in a monogamous relationship with an uninfected partner, or proper and consistent use of condoms.
Discussion 5.5 HIV Testing and Treatment
HIV testing looks for the antibody to HIV rather than the virus, thus testing is not accurate until several weeks (and possibly up to six months) after infection.
There is currently no vaccine against infection with HIV nor is there a cure. Treatment of HIV involves continued combination drug therapy that attacks the virus in a number of different ways. This treatment is called HAART or highly active antiretroviral therapy. Successful HAART treatment can result in an undetectable viral load but as soon as treatment is stopped the virus resumes replication and HIV continues its progression to AIDS. Vertical transmission (passing of the virus from mother to unborn child) can be reduced by around 65% if antiretroviral treatment is administered beginning at twelve weeks into the pregnancy. The list below shows some of the types of drugs being used in HAART and the effect they have on the HIV Virus.
| Entry Inhibitors | Prevents the virus from binding to the host cell |
| Reverse Transcriptase Inhibitors (AZT) | Prevent the RNA of HIV from being transcribed to DNA |
| Integrase Inhibitors | Prevent HIV from putting its DNA into the host cell |
| Protease Inhibitors | Prevent the enzyme protease from splitting polypeptides |
| Assembly and Budding Inhibitors | (In developmental Stage) Prevent the virus from budding from one cell and moving on to another host cell |
References
Image References
Images obtained from Aris site for Human Biology by Sylvia Mader (http://highered.mcgraw-hill.com/classware/selfstudy.do?isbn=0072986867 chapter resources - power point presentation), unless otherwise cited under image.
1 comments:
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