The most interesting system of our body that works all through the time but is hardly spoken of is the immune system. It is the system that protects our bodies from external invaders like bacteria, viruses etc that enter through our nose, mouth, skin, eyes etc.
After getting into the body, a toxin has to deal with the immune system at a different level. For example, tears and mucus contain an enzyme that breaks down the cell wall of many bacteria. Saliva is also anti-bacterial. Since the nasal passage and lungs are coated in mucus, many germs not killed immediately but are trapped in the mucus and soon swallowed. The main components of the immune system are described below.
The spleen filters the blood looking for foreign cells and also replaces old red blood cells.
Lymph nodes are similar to blood vessels except that they are passive, meaning there is no pumping of blood into lymph nodes. Fluids ooze into the lymph system and get pushed by normal muscle motion to the lymph nodes. Lymph nodes contain filtering tissue and a large number of lymph cells. Lymph is the blood plasma or the liquid that makes up blood without the red and white cells. Basic function of lymph is to carry food, water, and oxygen to each cell for its survival. The cells produce proteins and waste products and the lymph absorbs these products and carries them away. When fighting certain bacterial infections, the lymph nodes swell with bacteria. Swollen lymph nodes are therefore a good indication that there is an infection of some sort.
The thymus lives in our chest next to the heart. It is responsible for producing T-cells. T cells can detect cells infected with viruses and kill them. They are especially important in newborn babies without which a baby will die.
Bone marrow produces new red and white blood cells from stem cells. They are called "stem cells" because they can branch off and become many different types of cells. In the case of red blood cells, the cells are fully formed in the marrow and then enter the bloodstream. In the case of some white blood cells, they mature elsewhere.
Antibodies are Y-shaped proteins produced by white blood cells. When an antibody binds to the outer coat of a virus particle or the cell wall of a bacterium, it can stop their movement through cell walls.
Complement system is a series of proteins. There are millions of different antibodies and a handful of proteins floating freely in our blood. Complement proteins are produced in the liver. They are activated by and work with the antibodies. A large number of antibodies can bind to an invader and signal to the complement system that the invader needs to be removed. They cause bursting of cells and signal that a cell needs to be removed.
Several hormones are generated by components of the immune system. Some hormones suppress the immune system while others encourage lymphocyte production.