There are billions of microbes in the world that we come in contact with throughout our life. Not all of those microbes are helpful to our body, but that is why we have an immune system. Our microscopic immune system helps to maintain our body at a constant equilibrium. There are many way the immune system helps to provide that defense to harmful organisms. Tiny cells identify these foreign cells, and work to eliminate them from our body. When we are exposed to an organism, the body remembers that it was harmful, and if exposed again, the body can get rid of it faster. From the day of birth, our immune system is constantly being introduced to new molecules. The interactions between cells, different defense mechanisms, and the building of immunity helps to keep our body at homeostasis.


Concept #1: Defense mechanisms

There are many different ways the immune system works to keep out harmful organisms. The innate, or nonspecific immunity are automatically given with each organism. There are factors of each organ that help to keep out unwanted particles. An example of the inherited immunity is the acidity of the gastric juice, and membranes that cover some of the body surfaces. If the inherited immunity isn't there, an immunity can be acquired through lymphocytes, or white blood cells. Not all immunities can be inherited. Throughout your life your white blood cells have genetic changes within themselves to defend against pathogens. The genetic change of the white blood cells is called adaptive immunity. The innate immunity is the first line of defense for pathogens. The nonspecific, or innate, immunity has the ability to detect pathogens from the good body cells. The pathogen-associated molecular patterns, (PAMP's), are a unique characteristic to a foreign invader to the body. Phagocytic cells are a part of the nonspecific immune system. There are three types of phagocytic cells; neutrophils, mononuclear phagocyte system, and organ-specific phagocytes. Phagocytosis is a function in which the cell wraps around a pathogenic cell and destroys it. Monocytes and macrophages are the cells that belong to the mononuclear phagoctye system. Unlike the innate immune defense, the adaptive or specific defense uses antibodies as its defense system. Antigens help to start the production of specific antibodies. There are many ways the immune system uses defense mechanisms to fight pathogens.

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Concept #2: Lymphocytes and lymphoid organs

Lymphocytes, also known as white blood cells, originate in the bone marrow by specialized cells called stem cells. There are two main kinds of lymphocytes, T lymphocytes and B lymphocytes. The thymus is the main sight for production of T lymphocytes. B lymphocytes are made and found in the bone marrow. The primary lymphoid glands are the bone marrow and the thymus. By secreting antibodies into the blood and lymph the B lymphocytes can fight bacterial infections. Lymph is a fluid of the body as well as blood so they are able to provide humoral immunity. The T lymphocytes do not secrete antibodies to destroy a pathogen. Coming close to the foreign molecule will call the T lymphocyte to destroy the pathogen. Cell mediated immunity is caused by the T lymphocyte getting close to the host cell and killing it. Some of the secondary lymphoid organs include the tonsils, spleen, lymph nodes, and a patch under the mucosa of the intestine called the Peyer's area. Blood is filtered by the spleen while the other secondary lymphoid organs filter lymph. The secondary lymphoid organs are where pathogens are caught and kept so the lymphocytes can get close to them. The tiny T and B lymphocytes have such a big responsibility to the body, as well as all of the lymphoid organs.

Concept #3: Function of T and B lymphocytes

T lymphocytes are specific cells that are activated by antigens to prevent a pathogen from doing harm or damage to the body. Killer T cells are a type to T lymphocyte that has a specific molecule on the surface called CD8. The main function of the killer T cells is to destroy the cells in the body that are holding the foreign molecule. Killer T cells destroy the pathogen by cell mediated destruction and must come in physical contact with the bad cell. When the pathogenic cell comes in contact with the killer T cell, the killer T cell secretes chemicals to aid in the process of destruction. Perforins are a molecule that is secreted, and granzyme is an enzyme that is secreted by the killer T cell. CD4 on the outside of a molecule would indicate a helper T cell. The helper T cell basically helps many other cells do their job to get rid of the pathogen. Helping the B lymphocyte secrete specific antibodies and increasing the skills of the killer T cells are some tasks the helper T cell does. Lymphokine is a chemical regulator that is secreted by the helper T cell to complete those responsibilities. Suppressor T lymphocytes put the stop on the specific immune response. T lymphocytes help the immune system keep the body healthy. B lymphocytes on the other hands secrete antibodies to fight pathogens. When a B lymphocyte finds a pathogen, it then enters the germinal center os a secondary lymphoid organ. Inside the germinal center the B lymphocytes undergoes many divisions, where some of the cells become memory cells. Memory cells are like clones of the B cell, which has the antigens of the pathogen on it. If the cells aren't made into memory cells, they are made into plasma cells. Plasma cells produce about 2,000 antibody proteins per second. Being able to remember what pathogen entered the body, and that it was harmful is key for B lymphocytes. Next time that pathogen enters the body, the body is able to recognize it, and destroy it even faster then the first time. On the outside of the pathogens is an antigen and the B lymphocytes have a receptor for those antigens. When the receptor and antigen combine, it causes the B lymphocyte divide even more and produce more antibodies. There are so many pathogens that our body comes in contact with throughout our life. These tiny cells, T and B lymphocytes play such a huge role in the immune system in maintaining homeostasis in the body.

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People get sick everyday. If I become a nurse I will be taking care of sick people all the time. The reason why people get sick is usually because of a pathogen that enters the body and causes harm. Without an immune system, the body wouldn't be able to fight off disease causing molecules. Understanding how to prevent disease is essential to coach and educate my patients to keep them from getting sick all the time. If I see a patient that keeps getting an infection on his or her skin, like an open wound, I would teach them that they need to wash the wound and keep it free from other areas that contain pathogens. Another example would be with HIV, and educating my patient who was just diagnosed that they need to practice safe sex. On a personal level, I have received many pathogens throughout my life and I have acquired an immunity for most of those pathogens. I have learned to wash my hands more often, stay away from sick people, and to go see the doctor when I get sick. As a healthcare worker understanding how the immune system works is important.

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Essential question:

There are many different kinds of immunity that the immune system offers. Passive, active, innate, adaptive, humoral, and cell-mediated are not all the same kind of immunities for the body. Active immunity is an immunity that requires a prior exposure to the antigens specific molecules. When the body is introduced to a pathogen that is less resilient, it's called a vaccine. The body then develops a memory of that pathogen so next time, if ever, it's seen again in the body, the second response is activated which is much faster and stronger then the primary response. Passive immunity is when a human receives antibodies that were produced in an animal or another human. Providing antibodies from another host, offers immune protection to the body. Immunological competence develops about a month after birth. During pregnacy, the fetus can also receive passive immunity from the mother. Active and passive immunities both receive molecules of the pathogen from the outside of the body, but from different sources. Another form of immunity that body offer is innate immunity, or nonspecific immunity. Innate immunity is the immunity that is inherited with the organ itself, and is the first line of defense when a pathogen enters the body. Adaptive immunity, or specific immunity, uses antibodies as it's main source of defense against foreign molecules. The job of the antibodies is specific to it's task therefore it's called specific immunity. Innate and adaptive immunties are similar in that the immunity comes from within the body, but differ in the way they fight pathogens. Humoral immunity uses B lymphocytes as it's main source of a fight against a pathogen. Blood and lymph are fluids of the body in which the B lymphocytes secreted it's antibodies, so humoral immunity is also called antibody-mediated immunity. T lymphocytes do not secrete enzymes and must come in physical contact with the pathogen itself to destroy it, therefore this action is called cell-mediated immunity. Both T and B lymphocytes fight against bacteria, but use different kinds of immune responses to complete their task. Innate and adaptive immunities both aid when there is a break in the skin which causes a local inflammation. Mast cells and macrophages which are located in the tissue release chemicals which attract cells to get rid of the bacteria. Cytokines and chemokines attract phagocytic neutrophils, and start the process of phagocytosis and complement activation. After a while the B lymphocytes start to make antibodies to the bacteria which are causing the infection. Opsonization is when the antibodies start phagocytosis. When the injury is still new and fresh, neutrophils send a message to attract monocytes, lymphocytes, and other cells that aid in the immune response. Neutrophils secrete many agents to the surrounding tissue that is infected, and thus liquifies the surrounding tissues which creates pus. Mast cells are found in most tissues and contain heparin and release histamine. Redness, warmth, swelling, pus, and pain are some of the symptoms of a local inflammation. Inflammation can be good and bad for the body.

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