The Eight Major Systems
The digestive system The excretory system The muscular system The respiratory system
The skeletal system The nervous system The circulatory systemThe immune system
The Immune System
The purpose of the body's immune system it to protect it from infection and disease. It is highly effective. If it wasn't, humans would be sick most of the time. Because it is so effective, we will have to be very careful while on our tour, or we might encounter problems with it. The first layer of defense on the human body is the skin. It is highly impermeable, and quite tough. Because of this, we will enter the body another way.
When the immune system responds to an invader, there are two kinds of responses: Specific, and Nonspecific. A specific response is keyed to the individual invader. A nonspecific response is much more general, and will attack anything that doesn't belong in the body.Some of the major components of the human immune system are: bone marrow, the thymus, lymph vessels, lymph nodes, and the tonsils. The two most important of those are the bone marrow and the thymus where B and T lymphocytes are created.
The B cells are responsible for creating antibodies which bind onto a specific protien, making it easier for the other defense cells to identify it. Some antibodies also inactivate their target when they bind to it. T cells play a much more active roll in the immune response. Unlike the B cells which work mainly against viruses, bacteria, and the toxins they produce, T cells interact with other eukaryotic cells, particularly the body's own cells. They are capable of detecting whether a certain cell has been invaded by disease causing agents, and destroy it if it has. They are also the primary targets of the HIV virus. When HIV has killed sufficient T cells, the bodies immune system breaks down, and AIDS ensues.To help the body fight against diseases, people have come up with something called Vaccination. When a person is vaccinated, they are given a much weaker form of the same disease, which triggers the body to produce the memory cells for that particular antigen, thus allowing the person to resist that disease if they catch it in the future.
Perhaps one of the most annoying things about the immunne system is allergies. Allergies result from antibodies that attach themselves to mast cells. Then, when the correct antigen for that antibody comes along, the mast cell bursts, releasing a dose of histamine into the surrounding tissue and inducing the inflamitory response.