Body System
The immune system is the system of specialized cells and organs that protect an organism from outside biological influences. (Though in a broad sense, almost every organ has a protective function - for example, the tight seal of the skin or the acidic environment of the stomach.) When the immune system is functioning properly, it protects the body against bacteria and viral infections, destroying cancer cells and foreign substances. If the immune system weakens, its ability to defend the body also weakens, allowing pathogens, including viruses that cause common colds and flu, to grow and flourish in the body. The immune system also performs surveillance of tumor cells, and immune suppression has been reported to increase the risk of certain types of cancer.
The immune system is often divided into four sections:
* Natural passive immunity: Hereditary immunity, acquired from the mother, and lasting the first six months of a child's life
* Acquired passive immunity: Non-permanent immunity gained from vaccines, such as Rabies or Tetanus
* Natural active immunity: Having suffered a disease and its symptoms, one has natural active immunity, also known as a secondary response, where B-Cells fire off antibodies to combat a recognized antigen.
* Acquired active immunity: Permanent immunity as a result of vaccine.