Homeostasis (maintaining equilibrium) is essential for organisms to survive. The following are examples of certain adaptations that organisms use to maintain homeostasis.

The Immune System

The human body has a complex system to protect itself from foreign organisms. The first line of defense is made up of skin, mucus membranes, sweat, tears, hair, saliva, digestive enzymes, and stomach acid. The second line of defense is the inflammatory response. When histamines detect a foreign body, they send a signal which attracts macrophages through positive chemotaxis. The local capillaries swell and temperature increases in order to remove the foreign substance. The first two lines of defense are nonspecific, meaning that the same cells have the same reaction to any antigen. The third line of defense is the acquired/adaptive immune response. Specific memory B cells travel throughout the body looking for particular antigens. Each bacteria or virus matches with a specific B cell. If there are no or very few B cells for a specific virus or bacteria, the immune response will take longer to react. When a B cell is activated by the presence of an antigen, it marks the body for destruction, and a cytotoxic T cell destroys it.

First vs. second exposure

The first time a person is exposed to a disease, it takes much longer for antibodies to form and therefore it takes longer for the disease to be cured. This is because antibody production only begins when B cells recognize the antigen which triggers a larger immune response. The second time a person is exposed to a disease, there are already many B cells in the blood which causes a much faster increase in the number of antigens.