Despite the critical importance of the immune system for good health, many people have never heard of several key parts of the immune system. For example, there is a pretty good chance you didn't know you have a thymus. Yet it's right next to your heart. Other parts of the immune system are just as obscure.
You can see the most obvious parts of the immune system. For example, skin is one important part. Skin acts as the first boundary between germs and your body. One part of the skin's job is to act as a barrier. Think of skin in the same way you think of plastic wrap protecting food. Skin is generally impermeable to bacteria and viruses. The skin contains special cells called Langerhans cells that are an important early-warning component for the immune system. The skin also secretes antibacterial substances. This explains why people don't wake up each morning with a layer of mold growing on their skin—most bacteria and spores that land on skin die quickly.
A person's nose, mouth and eyes are obvious entry points for germs. Tears and mucus contain the lysozyme enzyme that breaks down the cell wall of many bacteria. In the mouth, saliva is an anti-bacterial. The nasal passages and lungs are coated in mucus, therefore, many germs not killed immediately are trapped in mucus and swallowed. Special cells called "mast cells" also line the inside of the nose, throat, lungs and skin. Bacteria or viruses that want to gain entry to the body must first make it past these defenses.
Once inside a body, a germ deals with a different level of the immune system. The major components of the immune system are:
- The thymus
- The spleen
- The lymph system
- Bone marrow
- The white blood cells
- The complement system