For movement( like in running), our muscles need oxygen. How do they get it? This question will be answered in this compendium review. Photo from: www.sheknows.com/articles/803849.htm I. Introduction to Cardiovascular System
II. Heart and Blood Vessels
- Types of Blood Vessels
- Heart
- Two Pathways
- Capillary Exchange
- Disorders
III. Blood
- Function and Composition
- Red blood Cells
- Platelets
- White Blood Cells
IV. Lymphatic System: Immunity
- Microbes and Pathogens
- Lymphatic system and Organs
- Nonspecific Defenses
- Specific Defenses
- Acquired Immunity
- Problems and Disorders
V. AIDS
- What is it?
- Where did it come from and where is it now?
- Phases
- Structure and life Cycle
VI. Conclusion
I. Introduction
The drawing above illustrates a capillary bed. The red tube illustrates an artery and the blue tube is a vein. In between is the capillary bed. There is also a close up on the right. Human Biology, page 87. Sylvia S. Mader
Heart
Illustration of locations for measuring pulse. Human Biology, page 92. Sylvia S. Mader
Two Pathways
The pulmonary circuit circulates blood through the lungs, and the systemic circuit caters to the needs of the body tissues. The purpose of the pulmonary circuit , if I am understanding it correctly, is to take blood that is O2 poor through the lungs which then enters the left atrium (now oxygen rich) and then is pumped through the body. The systemic circuit is where exchanges with tissue fluid occur and involves all the arteries and veins shown in the figure below. The aorta, the largest artery, receives blood from the heart, and the superior and inferior venae cavae return blood to the heart.
I appreciated this diagram and it was especially useful in identifying the two cardiovascular pathways. Human Biology, page 94. Sylvia S. Mader
Capillary Exchange
As I mentioned before, exchange occurs in the capillaries. This occurs in the midsection with molecules like oxygen and glucose, following their concentration gradients, end exiting the capillary, while wastes and CO2 diffuse into the capillary. Movement of fluid is controlled by blood pressure and osmotic pressure. Blood pressure is higher at the arterial end of the capillary causing water to exit. At the venous end, osmotic pressure is higher, causing water to diffuse into the capillary. At this end almost the same amount that diffused out on the arterial end diffuses into the capillary.
A diagram illustrating capillary exchange. Human Biology, page 96. Sylvia S. Mader
Disorders
It seems like we hear so much about more sensational diseases but the fact is cardiovascular disorders like hypertension, heart attack, and stroke, are the leading cause of death in the USA.
High blood pressure (AKA hypertension) happens when blood moves through the arteries at a higher than normal pressure. As stated before, a normal adult blood pressure is around 120/80. A person has hypertension if the systolic reading is consistently above 140 and/or the diastolic is consistently above 90. It is not unusual for individuals with atherosclerosis, plaque in the arteries, to suffer from hypertension. Unfortunately people with this condition can be asymptomatic for for a long time before the problem is discovered.
Sometimes when plaque is present a clot called a thrombus can form on the arterial wall. If the the clot becomes a thromboembolism, complications like stroke, heart attack, or aneurysm can occur. All three of these are associated with hypertension and atherosclerosis, and all three can result in death. A stoke occurs in the brain and often happens because a cranial arteriole bursts or is blocked by an embolus. A heart attack (AKA myocardial infarction) occurs when a part of the heart muscle dies because of a lack of oxygen. An aneurysm is caused by a ballooning blood vessel.
Diet and physical activity play a role in cardiovascular disease. A sedentary lifestyle and high fat diet can increase the risk of these conditions. Smoking and obesity are also factors. Sometimes individuals have a hereditary predisposition for these kinds of disorders as well.
There are other disorders of the cardiovascular system like heat failure, heart transplants,and dissolving blood clots that are not detailed here.
I got this picture from the National Geographic website, it is an image of red blood cells. http://science.nationalgeographic.com/science/health-and-human-body.html
III Blood
Function and Composition
We already learned in the last unit that blood is a connective tissue. Our bodies contain approximately 5 liters of this fluid. There are three basic functions of blood, transport, defense, and regulation.
Transport: Blood has the role of delivering oxygen and nutrients to the tissues. It also serves in the role of garbage collector, picking up CO2 and other wastes.
Defense: The blood contains certain cells that are able to destroy pathogens and other harmful substances. Some of these cells also produce antibodies that are able to incapacitate pathogens for destruction. The blood is also capable of clotting when an injury occurs which prevents blood loss.
Regulation: The blood assists in regulating body temperature. Blood also helps to maintain its own water-salt balance. Therefore, blood plays a role in homeostasis.
The blood is composed of cells and cell fragments (known as formed elements) suspended in a liquid called plasma. The formed elements include red blood cells, white blood cells, and platelets. These elements are produced in red bone marrow. The liquid medium carrying different substances in the blood is known as plasma. Plasma is 91% water with 9% consisting of various salts and other organic molecules. There are three major types of plasma proteins, albumins, globulins, and fibrinogen.
Diagram showing the different types of blood cells produced by stem cells in the bone marrow, page 106. Human Biology, Sylvia S. Mader
Red Blood Cells
Red Blood cells (RBCs) are produced in the bone marrow by stem cells. RBCs are very specially designed to transport oxygen. They do not contain a nucleus, but instead contain hemoglobin, a pigment that is responsible for giving red blood cells and blood a red color. There are about 4-6 million RBCs in every cubed mm of blood! An estimated 2 million red blood cells are destroyed per second in the liver and spleen. Sometimes individuals do not have enough hemoglobin or an insufficient number of red blood cells, this condition is called anemia.
It is the shape of red blood cells that makes them specially suited to carry oxygen. The lack of a nucleus helps create their biconcave shape. In sickle cell disease, red blood cells have an irregular shape and tend to rupture when they pass through narrow capillaries.
This is a photo of sickle cells I found at www.nlm.nih.gov/.../ency/imagepages/1223.htm
Hemoglobin transports about 25% of CO2 and 7% is dissolved in plasma. The remaining 68% is transported as the bicarbonate ion in the plasma. When it reaches the lungs (via blood), CO2 diffuses out of the blood.
Platelets
Everyday our bodies produce 200 billion platelets. Platelets/thrombocytes are responsible for causing blood to coagulate and clot. When a blood vessel is broken, platelets will clump together at the site of the damage and form a seal. Larger punctures or cuts may require a blood clot to prevent further bleeding. My father suffers from a condition called ITP, Idiopathic thrombocytopenic purpura, his platelets are extremely low and it seems to have something to do with his antibodies attacking his platelets. He is at a high risk if he is injured because of his low platelet count. Another blood clotting disorder is Hemophilia, which is genetic.
White Blood Cells
White blood cells (AKA leukocytes) fight infection. Many of them are phagocytic, meaning they can engulf and destroy pathogens. These cells are larger than RBCs, contain a nucleus, lack hemoglobin, and are translucent. There are also fewer white blood cells than RBCs. There are several different types of white blood cells and they are regulated by a protein called a colony stimulating factor. The two classifications for white blood cells are granular leukocytes and agranular leukocytes. This is because some have noticeable granules and some do not.
Granular Leukocytes: Neutophils, eosinophils, and Basophils are all granular leukocytes. 50-70 percent of all white blood cells are neutrophils, making them the most common white blood cells. Neutrophils are phagocytic and usually respond first to a a bacterial infection. Their death after fighting an infection results in pus.
Not much is known about the function of eosinophils, but they do have a role in dealing with an allergic reaction or fighting a parasitic worm infection.
Basophils have a U-shaped nucleus and become a blue color when stained. Basophils work in the connective tissues to release histamine during a allergic reaction. Histimine works to dialate the blood vessels but also constricts the air tubes leading to the lungs.
Agranular Leukocytes: Lymphocytes and monocytes are agranular leukocytes. They do not have granules and their nonlobular nucleus has caused them to be called mononuclear leukocytes.
Monocytes can be found in the tissues where they differentiate into macrophages, and are the largest of the white blood cells.. In the skin they become dendritic cells. Macropgages and dendritic cells phagocytize old cells, cellular debris, and pathogens as well. They can also stimulate other white blood cells to come to the body's defense.
Here is a macrophage engulphing invading microbes, taken from Professor Frolich's power point.
Lymphocytes are the white blood cells responsible for specific immunity to different poisons and pathogens. Lymphocytes can be B-cells or T-cells. The descendants of B-cells (AKA plasma cells) produce antibodies. Antibodies are proteins that combine with certain pathogens, marking them for destruction. Cytotoxic T-cells directly destroy pathogens, and the AIDS virus attacks T-cells affecting an individual's ability to fight infection.
Lymphatic System and Immunity
Microbes and Pathogens
Our bodies need to have defenses against pathogens like bacteria and viruses. Bacteria are prokaryotes and do not have a nucleus. Bacteria are the most abundant lifeform on the planet and most do not actually cause disease. However some can be harmful and even kill us. Strep throat, syphilis, and tuberculosis are bacterial diseases.
Viruses are acellular and cannot live independently of cells. Diseases like colds, flus, measles, and AIDS are caused by viruses. Virus particles are significantly smaller than bacteria. There are two parts to viruses, the outer capsid and an inner core of nucleic acid. Although there are many different viruses, they all have these two subunits. Viruses take over the metabolic machinery of the host cell. Once inside a host cell, the virus relies on that cell's enzymes and ribosomes to reproduce.
Examples of viruses, adenoviruses cause colds and influenza viruses cause the flu. Notice that although different, both contain the two subunits, page 123. Human Biology, Sylvia S. Mader
Lymphatic System and Organs
The lymphatic system includes the lymphatic vessels and the lymphatic organs. The vessels form a system consisting of capillaries, vessels, and ducts that carry lymph to cardiovascular veins in the shoulders. The lymphatic capillaries take up excess tissue fluid. The fluid inside lymphatic vessels is colorless and called lymph. There are two ducts in the lymphatic system, the thoracic duct and the right lymphatic duct.
There are primary lymphatic organs like red bone marrow and the thymus gland, and secondary organs which are the lymph nodes and spleen. The red bone marrow is where white blood cells mature while the spleen and lymph nodes are staging areas. The spleen is the largest lymphatic organ and filters the blood. Lymph nodes filter lymph. Lymph nodes can be found at various sites throughout the body including armpits and at the groin area. Lymph nodes around the neck will sometimes swell up when an infection is present.
Nonspecific Defenses
Nonspecific defenses include barriers to entry and the inflammatory response.
The skin is a very effective barrier to pathogens. Of course a cut or abrasion causes a tear in that barrier and can provide access to pathogens. Mucous membranes found in the respiratory, digestive, urinary, and reproductive tracts also serve as barriers to infection.
Chemical barriers also provide nonspecific defense. Chemical barriers are found in secretions from the oil glands in our skin. The secretions from these sebaceous glands contain chemicals that can weaken or even kill bacteria. Lysozyme is found in saliva, tears, and perspiration and it also kills bacteria. Stomach acid kills or stops the growth of many types of bacteria.
There are certain kinds of bacteria that normally live in the mouth, intestine, and other parts of the body. These bacteria consume nutrients and cause waste that prevent harmful bacteria from living there. This actually makes these bacteria a nonspecific defense.
Specific Defenses
Specific defenses are important when nonspecific defenses are unable to prevent an infection. Once an antigen has gained entrance to the body, specific defenses go to work to destroy it. Specific defenses also work to protect us from cancer. Lymphocytes, B and T cells, are the main players in specific defense. These cells recognize invading antigens by using their specific antigen receptors. The shape of these receptors allows B and T cells to combine with the antigen. Each Lymphocyte has only one type of receptor, therefore we need lots of different B and T cells to protect us from all the different antigens that exist in this world. It is amazing to me that our bodies have this ability! In 1987 (the year I graduated from high school), Susumu Tonegawa won the nobel prize for his findings regarding antibody diversity.
B and T cells differentiate into other types of cells to play different roles in fighting disease. For example, B cells become Plasma cells and memory B cells. B cells with a receptor for a particular antigen are stimulated to clone themselve, most of those cloned B cells become plasma cells and some become memory B cells. Plasma cells produce antibodies and memory cells help create long term immunity. B cell defense is known as antibody mediated immunity.
Antibodies are Y-shaped protein molecules with antigen binding sites at the tips of the Y. Each arm of the antibody includes a "heavy" polypeptide chain and a "light" polypeptide chain. There are constant regions for these chains located in the trunk of the Y where the amino acid sequence is set. 
A picture of an antibody taken from www.jdaross.cwc.net/humoral_immunity.htm
There are five classes of circulating antibodies. IgG antibodies are the main type in circulation, they even cross the placenta from the mother to the fetus. IgM antibodies are pentamers (clusters of five Y-shaped molecules linked together) and are the largest in circulation. They are the first antibody formed by newborns and the first formed with a new infection. IgA antibodies have two Y-shaped structures and are found in body secretions like saliva and milk. IgD antibodies are found on the surface of immature B cells. IgE antibodies are antigen receptors on basophils and are responsible for fighting off parasitic worm infections and have a role in allergic reactions.
T cells directly attack diseased cells and cancer cells, this is known as cell-mediated immunity. T cells have a unique T cell receptor, similar to B cells. However T cells could not recognize antigens without the help of an antigen-presenting cell (APC) like a macrophage. After an APC has phagocytized a pathogen, it travels to a lymph node or the spleen where there are T cells. By displaying the foreign protein on its surface, the APC is able to "activate" the T cell (and its offspring) to recognize the pathogen. Cytotoxic T cell are the ones that go out and actually destroy the pathogens, they are also responsible for cell-mediated immunity. Helper T cells regulate immunity by secreting cytokines, which are chemicals that enhance the response to immune cells. Helper T cells do not fight infections directly. Memory T cells (like memory B cells) remember the antigen and can start an immune reaction to an antigen that was previously present in the body.
Diagrams of the different kinds of B and T cells. Figure on the left shows B cells and the one on the right shows T cells, pages 131 and134. Human Biology, Sylvia S. Mader
Aquired Immunity
There are two types of aquired immunity, active and passive. Active immunity occurs when a person developes antibodies against a particular pathogen. This can happen naturally when an individual gets infected and after they are well, produces antibodies against that particular infection. Sometimes active immunity is induced through the use of vaccines like DPT or polio. In Passive immunity, a person is actually give specific antibodies through an injection. Passive immunity is temporary because the antibodies were not actually produced by the individual's plasma cells.
Disorders
Autoimmune diseases like MS or Lupus occur when a person's cytotoxic T calls or antibodies attack the body's own cells. We do not know what causes autoimmune diseases. Sometimes a person has an immune deficiency where the body is no longer able to protect itself from disease. This is the case with AIDS. I will cover AIDS in the next section.
V. AIDS
What is it?
The human imminodeficiency virus (HIV) causes aquired immunodeficiancy syndrome (AIDS). The virus weakens the immune system by infecting cells, especially helper T cells and macrophages. Because their immune system has been compromised, people who have HIV are more susceptible to opportunistic infections that take advantage of the weakened immune system. Like many viruses, there is more than one strain of HIV, but there are two main types, HIV-1 and HIV-2, with HIV-1 being the more powerful and common strain. The advanced stage of HIV is known as AIDS. When an infected individual progresses to AIDS they begin to develop more and more opportunistic infections.
Where did it come from and where is it now?
Most scientists believe that HIV originated in Africa. It is also thought that modern day HIV may have evolved from an immunodeficiency virus sometime in the 1950s. The virus has been further traced to similar viruses found in primates, and researchers have speculated that the virus may have mutated after people ate meat from primates.
British scientists have proven that AIDS came to their county sometime around 1959, and American scientists believe that HIV entered the US around the 1950s as well. The first documented American case of the virus was in a 15 year old boy who died in 1969. The boy died with skin lesions caused by a cancer now widely associated with AIDS. AIDS was not identified as the cause of death in many cases because the disease is not extremely infectious and patients die of oppurtunistic infections rather than the disease itself. It was in 1982 that the term AIDS was coined and HIV was found to be the cause of AIDS in 1983-84.
AIDs is prevalent in the human population all over the world, making it a pandemic. An estimated 38.6 million people today are living with HIV infections, 2.3 million of which are children. Almost 25 million people have died of AIDs since the epidemic began and today almost 1% of the world's adult population have HIV.
Sub-Saharan Africa are among the hardest hit regions. There are approximately 24 million people in Sub-Saharan Africa and 8.3 million in Asia living with HIV infections. North America, western and Central Europe have about 2million HIV infections. In the US African Americans and Hispanics made up about 70% percent of all newly diagnosed HIV/AIDS infections. Although AIDS is still a problem in the USA, obviously the real epedemic is in Sub-Saharan Africa and Asia.
Public health professionals like myself have dealt with HIV/AIDS in the context of TB infections. There was a lot of useful information on HIV and its relationship to TB at http://healthinitiative.org/html/index.htm.
Map of Africa showing where AIDs has become an epidemic. I took this picture from professor Frolich's PowerPoint.
To the right is a picture of HIV taken from www.healthinitiative.org/.../hivbig.htm
Phases and categories
There are different subtypes of HIV infection, some are more common in other parts of the world. For the purpose of this categoriztion I will be referencing HIV1B. There are basically three categories of infection, the acute phase, chronic phase, and AIDS.
Acute phase: During the acute phase the infected person is usually asymptomatic, in fact they most likely do not know they are infected and feel fine. Sometimes however there are flu-like symptoms during the first few weeks of infection. It is important to remember that the infected individual is still able to transmit the virus even if they feel fine. At this stage the CD4 T cell count will still be high and will never have fallen below 500, so in other words, the immune system still functions like normal. The viral load, the number of HIV particles in the blood is also still lower than the CD4 T cell count.
Chronic phase: Once a person's CD4 T cell count has dropped between 499 and 200 they may begin to display symptoms. There are many different symptoms that may show up at this stage, some of the more common ones are yeast infections, fatigue, shingles, unexplained fevers, sores on the mouth or tongue, and swollen lymph nodes. Also the viral load will begin to rise during this stage of infection.
AIDS: Remember that HIV is the virus that causes AIDS, the breakdown of the immune system. During the AIDS phase the infected individual will have a CD4 Tcell count below the 200 mark and/or will have one of the opportunistic infections common with AIDS. There are over 25 of these AIDS-defining illnesses. To name a few: Mycobacterium Tuberculosis, which is a bacterial infection that gets into the lymph nodes or lungs, Pheumocystis jiroveci pneumonia is a fungal infection of the lungs, and kaposi's sarcoma is a rare cancer of the blood vessels. Once a person is diagnosed with AIDS they usually die within two to four years, however new drugs have been developed to fight these infections and patients are living longer. It is important to remember that it is not AIDS that actually kills the person but the opportunistic infection brought about by the compromised immune system.
Structure and Life Cycle
As I mentioned earlier, viruses cannot live outside of cells and HIV is no exception. HIV is a retrovirus and is a single strand of RNA surrounded by proteins. Once the virus gets into a cell it inserts itself into the DNA and using a protein called reverse transcriptase it bigins to copy itself. Then it wraps itself up in proteins and "buds" out of the cells, pretty insidious if you ask me!
I found this micrograph of HIV buddng from a white blood cell at http://science.nationalgeographic.com/science/photos/aids/aids-virus.html. the website offers an interesting slide show about HIV and AIDS.
HIV infects helper T cells. Helper Tcells are the ones that stimulate cytoxic T cells and B cells. In other words the helper T cells are the ones responsible for the immune response, they do not actually kill antigens themselves. So once a helper T cell is infected with HIV it recognizes that it is now itself an antigen and it calls in the troops. This is how the helper T cells are killed off by the other cells. Once the helper T cells are at dangerously low levels the body is no longer equipped to fight off opportunistic infections.
From the powerpoint presentation, this picture shows how HIV gets into the cell and replicates itself.
I got this graphic at http://www.biology.arizona.edu/immunology/tutorials/AIDS/HIVimmune.html from the web links, It shows the progress of the disease. I appreciated this particular website, I thought it was very informative
To wrap up this portion on HIV/AIDS I should mention how it is transmitted. HIV is transmitted by blood and other bodily fluids, it is not airborn. It also does not last long outside the blood. It can be transmitted through sexual intercourse, infected blood, by sharing needles, and in some cases through a mother's milk.
IV. Conclusion
Basically I think the main thing I got out of this major topic was an understanding of how the body systems work together to maintain homeostasis. How the respiratory system is linked to the cardiovascular system, how our blood is so closely linked with the immune system. I also appreciated the section on AIDS. I had a very special friend and mentor who died of AIDs in the late 1980s. We met when I was recovering from an illness at UCLA medical center, he was a volunteer there. He never discussed his condition with me, maybe because I was so young (I was only 15 at the time I knew him) and AIDS was a big news item at the time. I remember him telling me about having Karposi's Sarcoma and showing me his hands which were covered in lesions. My family moved and I lost touch with him before he died. It was not until I was an adult and learned of his death that I began to put it all together and asked my father about him. My father admitted that my friend died of AIDS. I have always felt cheated that I did not get the opportunity to show my friend that I did not care that he had AIDS, of course I loved him no matter what. I just hope he was trying to protect me rather than keeping it from me out of fear of rejection. I hope that eventually we find a way to erradicate this terrible disease.
Works cited
Human Biology, Sylvia S. Mader
Blood, Oxygen, and Immunity,power point- Larry M. frolich
www.sheknows.com/articles/803849.htm
http://www.biology.arizona.edu/immunology/tutorials/AIDS/HIVimmune.html
http://science.nationalgeographic.com/science/photos/aids/aids-virus.htmlwww.nslc.wustl.edu/sicklecell/sicklecell.html
www.healthintiative.org
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