Blood passes through tiny blood capillaries all over the body. *These capillaries allow fluids to leave in order to carry nutrients to the cells of the body. *Some of this fluid returns to the blood capillary, but not all of the fluid is able to reenter the capillary. The extra fluid is drained away by the lymphatic system.
Lymphatic capillaries are shown in green on this slide. They are better able to absorb fluid than blood capillaries. Lymphatic capillaries connect to lymphatic vessels that transport fluid throughout the body.
The lymphatic system serves several important functions in the body. *It drains fluid from around cells to prevent fluid build up. *Lymphatic capillaries are also able to absorb fat from the intestines. *The fluid that is circulated by the lymphatic system is called lymph. Lymph is filtered by the lymphatic system to remove such things as microorganisms and wandering cancer cells. *The lymphatic system also gives us our immunity.
Two major blood vessels drain lymph from the entire body. *The right lymphatic duct drains the upper right quarter of the body. It carries lymphatic fluid from the area of the body shown in green. The fluid empties into the right subclavian vein. *The rest of the body is drained by the thoracic duct that empties into the left subclavian vein.
Lymph is the fluid of the lymphatic system. It is similar to blood plasma and interstitial fluid. When the fluid is in the blood stream it is called plasma. When the fluid is between cells it is called interstitial fluid. Lymph is the term for the fluid when it is in the lymphatic system.
Lymphatic vessels function to transport lymph. They are found throughout the body just like arteries and veins. Lymph is returned to the circulatory system at either the right or left subclavian veins.
Lymph nodes are especially numerous in the neck, axillary and inguinal regions of the body. They filter microorganisms and cancer cells from lymph. Lymphocytes and monocytes are found in the lymph nodes. Their function will be discussed later in this presentation.
The thymus is located below the larynx. It programs lymphocytes to develop into T-cells.
The spleen filters the blood of worn out red blood cells and bacteria from the blood. Lymphocytes and monocytes are also found in the spleen.
When the heart beats it creates a hydrostatic pressure forcing fluid out of blood capillaries. As mentioned before, the fluid carries nutrients to cells of the body. The fluid in the interstitial spaces must return to the circulatory system to maintain homeostasis. Some fluid returns to the blood capillary and some travels through the lymphatic system.
Edema is the accumulation of interstitial fluid.
There are several causes of edema. * A blockage of the lymphatic system can prevent fluid from draining and cause edema. *Increased pressure in veins can also result in edema. This often happens during pregnancy when the growing fetus puts pressure on the mother’s vena cava. *Lack of albumin in the blood is another cause of edema. Albumin is needed to attract fluid back into capillaries by osmosis. If the blood does not have enough albumin it cannot return as fluid from the interstitial spaces. *Inflammation can also cause edema. During inflammation capillaries dilate to allow antibodies, white blood cells and other factors into the inflamed area of the body.
The body has several nonspecific defenses that help to keep a wide variety of microorganisms out of the body. They are called nonspecific because they are not designed to target any microorganism in particular, but to protect us from all microorganisms. As long as the skin is intact it will keep out most pathogens or disease causing organisms. Acid in the stomach and vagina will kill many microorganisms. Mucus in the respiratory and digestive systems will trap microorganisms so they can be destroyed. Saliva and tears have enzymes that destroy many bacteria.
Phagocytosis is the engulfing of cells. Many of our white blood cells have the ability to engulf foreign cells and destroy them. Complement is a protein in the blood that literally pokes holes in unwanted cells to destroy them. A fever is a natural mechanism to fight microorganisms. The increased temperature causes our immune system to work faster. Also the fever will cause the liver to sequester iron. This makes it more difficult for bacteria to multiply. Inflammation is the body’s response to injury. It will be discussed in more detail later in this presentation.
This slide illustrates how complement works. Complement is a series of proteins that fit together to form a large pore in a cell. This pore will allow the contents of the cell to leak out. Complement creates a lethal hole in a cell just as a bullet can create a lethal hole in the body.
Inflammation is the body’s response to tissue injury. The classic signs of inflammation are heat, redness, swelling and pain.
The next few slides will illustrate the process of inflammation. The skin forms a barrier to keep microorganisms out of the body.
The inflammation process can begin if the skin or other tissues are damaged. *A pin penetrating into the skin can start an inflammation. *Bacteria may enter the body with the pin.
Injured cells will release histamine. *Histamine will diffuse away from the injured cells.
Histamine will cause capillaries to become more permeable. *This will allow plasma to leak out of the blood.
Antibodies will also leave the blood capillary*.
White blood cells will leave the blood by diapadesis*.
The plasma in the injured area will clot to form a wall of fibrin*.
Pus forms within the fibrin wall. The pus is composed of serum, white blood cells and bacteria. The pus will drain and scar tissue will form. At this point the injury to the body has been controlled and homeostasis will be restored. Without the inflammation process the injury could spread. For example, bacteria could spread throughout the body and cause death.
Hydrocortisone and cortisone are steroid hormones that depress inflammation. The body uses these hormones to regulate inflammation. These hormones are often used to treat inflammatory diseases such as rheumatoid arthritis. They do not cure the disease, but reduce the inflammation that is associated with the disease.
This diagram represents a cell with antigens on its surface. *Antigens are molecules often found in the membrane of cells. *Antigens of foreign cells simulate an immune response.
Self antigens are *antigens of our cells. *They do not cause an immune response in our body, but usually cause an immune response in another person. *Our own antigens make up our major histocompatibility complex or MHC proteins.
We will study different types of cells than make up our immune system. *Antigen-presenting cells or APCs are one these. *B-cells or B lymphocytes are another type. *T-cells or T lymphocytes are the third type. These are the major kinds of cells that constitute our immune system.
Antigen-presenting cells include macrophages and other cells that engulf foreign cells and attach the cells antigens on their MHC proteins. *This diagram represents an antigen-presenting cell with MHC proteins on its surface. *The yellow triangles represent antigens from a foreign cell. The APC previously engulfed the foreign cell. It has stripped the antigens from the cell and is now ready to present these antigens to bodies T-cells.
Two major types of lymphocytes make up the immune system. The T-cells are programmed in the thymus for a specific role in immunity. B-cells develop in the bone marrow. These lymphocytes migrate to the lymph nodes and other lymphatic tissue in the body. From there they can move in and out of the blood stream.
A B-cell is illustrated here. It has receptors on its surface that are capable of connecting with an antigen. *Note that the receptor and the antigen have complimentary shapes.
There are thousands of different possible shapes for B-cell receptors. Each type of B-cell has a unique receptor shape. In this slide the middle B-cell has receptors that are complementary to the antigen. * Only this cell will bind with the antigen. The other B-cells are not involved. The selected B-cell will now make clones of itself. * It will produce many other B-cells that are identical copies. *Each of these in turn will develop into a plasma cell. Plasma cells are B-cells capable of producing antibodies. *The plasma cells with produce identical antibodies. These antibodies will match the antigen of the foreign cell. The immune system can produce millions of antibody molecules once a B-cell has been stimulated by an antigen. Note that only the B-cell with a receptor that matches the antigen will multiply. It has been selected to reproduce. A few of the B-cell will become memory B-cells. They are stored in the immune system in case the same antigen again invades the body. The memory B-cells are capable of mounting a faster immune response. They will usually make antibodies to destroy the foreign invader before it can do any harm to the body.
Another type of T-cell is the cytotoxic T-cell or the killer T-cell. It has a receptor on its surface that will match a specific antigen. These cells are capable of reacting with body cells that have foreign antigens on their surface. * For example, a body cell infected with a virus will have viral antigens on the surface of the cell membrane. Cytotoxic T-cells are capable of destroying cells with foreign antigens.
This slide shows the process in more detail. *The body cell at the top has a viral antigen on its surface. *The antigen is complexed with an MHC protein on the body cell. *The cytotoxic T-cell combines with the antigen on the infected body cell. The T-cell is now selected to multiply. *The cytotoxic T-cell will make clones of itself as well as a few cytotoxic T memory cells.
Helper T cells require stimulation from an antigen-presenting cell. *When the APC and the helper T cell combine the helper T cell will be stimulated to make clones of itself.
The role of the helper T cells in both cellular and humoral immunity is illustrated on this slide. *The antigen-presenting cell will release interleukin I to stimulate the helper T cells. The helper T cell in turn will stimulate cytotoxic T cells and B cells. *It does this with interleukin II. The activated cytotoxic T cells provide cellular immunity. Cellular immunity is confirmed by cytotoxic T cells attacking infected or diseased body cells to destroy them. Humoral immunity is confirmed by antibodies that react with foreign invaders in ways that will be discussed later in this presentation.
When a cytotoxic T cell binds with a target body cell, it releases molecules of perforin that perforate the membrane of the cells causing it to die.
The next few slides will review important cells and molecules of the immune system. Antigen-presenting cells include macrophages and other cells that engulf and digest foreign cells. They present antigens on MHC proteins to T cells.
B cells are lymphocytes that react directly with antigens. They require stimulation from helper T cells. The offspring of the B cells are plasma cells and memory B cells. B cells provide us with humoral immunity. Humoral immunity is immunity provided by antibodies.
Plasma cells are antibody factories. They can produce up to 2000 antibodies per second.
Helper T cells react with antigens presented to them by an antigen-presenting cell. The helper T cells stimulate both cytotoxic T cells and B cells. They stimulate these cells with interleukin II. Helper T cells are the heart of the immune system. Without them the cytotoxic T cells and B cells will not be active enough to give us immunity.
Cytotoxic T cells are activated by antigens on body cells. To be effective they require stimulation from helper T cells. They cytotoxic T cells destroy body cells infected with viruses and they can destroy cancer cells. Cytotoxic T cells provide us with cellular immunity.
Memory cells are produced by both T cells and B cells. They remember the antigen and are able to react to a second invasion of an antigen more rapidly. For example, most people on get chicken pox once in their life. Even though they are exposed to the virus many time again they normally do get the disease twice because memory cells are able to respond faster.
Suppressor T cells stop T cells and B cells after an infection has been conquered.
Cytokines are chemicals used in cellular immunity. We are learning three of these. Interleukin I is produced by macrophages to stimulate helper T cells. Interleukin II is produced by helper T cells. It stimulates cytotoxic T cells and B cells to become more active. Perforin is produced by cytotoxic T cells. It will poke holes in a target cell to cause lysis.
Antibody molecules are shaped somewhat like the letter y. The main part of the molecule is the antigen binding site.* This is the end of the molecule that connects with an antigen. Often a single antibody molecule can bind with two different antigens.
There are several antigen antibody reactions. Neutralization is when antibody molecules cover dangerous parts of toxins or viruses. Agglutination binds cells together. Precipitation will bind soluble antigens. All three of these process enhance phagocytosis. Antibodies also activate complement to cause cell lysis.
There are five classes of antibodies. IgD attaches to the surface of B cells. It forms the B cell receptors. IgM is the largest of the antibodies. It often exists as a pentamer. It is usually the first type of antibody produced when the body is infected with a pathogen or disease causing agent. IgM is the type of antibody that agglutinates blood cells. Anti A and Anti B used in blood typing are in the class IgM.
IgG is the most abundant of the antibodies. It is able to cross the placenta to give a fetus immunity. Newborns get IgG from their mothers to protect them for the first few months of life. IgA is found in body secretions. These include saliva, sweat and mothers milk. IgA guards against pathogens entering through mucous membranes such as the mouth, nose and eyes. IgE helps the body release histamine during the inflammatory response. The level of IgE is elevated during an allergy.
Immunity can be naturally or artificially acquired. Also, immunity can be active or passive. Active immunity lasts for a long time. This is often many years to a lifetime. In active immunity the body makes its own antibodies. Passive immunity is short term. It typically lasts for just a few months. In passive immunity antibodies are borrowed from someone else. A natural way to get active immunity is have a disease and survive. After that time you will make antibodies to the pathogen. A natural way to get passive immunity is when antibodies pass from the mother to the fetus across the placenta. An artificial way to get active immunity is to be vaccinated with dead or weakened pathogen. An artificial way to get passive immunity is to receive an injection of antibodies made by someone else. Gamma globulin is the portion of serum that contains antibodies.
The next series of slides will illustrate how a virus attacks and destroys cells. A virus is composed of two main parts. It has a protein coat that surrounds a molecule of DNA or RNA.
A virus can attach to a body cell. *It will connect to a protein in the membrane of the cell.
After the virus attaches to the cell it may inject its DNA into the cell.*
The viral DNA has instructions for producing new viral protein coats. The viral DNA will use the machinery of the cell to synthesize new viral protein coats.*
Next the viral DNA is copied many times. A single copy of the viral DNA will go into each protein coat. The cell has been tricked into making many new viruses.
The viral DNA has a gene that will produce a protein to cause the host cell to lyse. When it does the new viruses are released to infect other cells.
The host cell is killed by the viruses.
Cells that are infected with a virus will often release a chemical called interferon. Interferon will block the entrance of the virus into neighboring cells.
AIDS is a disease of the immune system. It is acquired by becoming infected with the HIV virus. The virus attacks and destroys helper T cells. Helper T cells are the heart of the immune system. Without them both cellular and humoral immunity becomes depressed. AIDS patients often die of pneumonia or cancer because of a depressed immune system.
