Immune system – Powerful army of cells that fights against diseases
The immune system is made up of a network of cells, tissues, and organs that work together to protect the body.
Our body generally defends us against anything that is not recognized as being part of or belonging in our body. The immune system is the body's defense against invasion of antigens such as bacteria, viruses, pollen, additives, certain foods, and others. When a person is first introduced to an antigen, such as a flu virus, the immune system makes an antibody, or protective chemical, to fight off the invader. The next time the person is exposed to the same flu virus, the immune system remembers, recognizes the invader, and releases the specific antibodies that react with the virus and destroy it. Incredibly, the immune system can produce antibodies with the identical shape of the antigen they must bind with point for point in order to eliminate the antigen, allowing the person to recover. Our immune system's capacity for memory allows us to develop immunities. When our immune system knows what a germ looks like, it can stop any new infections before we get sick again. That means we are immune to that particular germ. Antibodies are made by white blood cells called lymphocytes, which originate in bone marrow and circulate through the bloodstream, patrolling all areas of the body to identify and protect against foreign invaders. When the lymph nodes in the body swell, it's actually because they're filling up with these cells which will attack the invader.
The body’s “strategy” for defending against foreign organisms, cells, or molecules has three phases.
- Keep the foreign cells or molecules out of the body
- Attack any foreign cell or molecule that enters the body
- Destroy the specific type of foreign cell or molecule that enters the body.
The body has three lines of defense, each accomplishing one of the phases in its defensive strategy. The first line of defense - chemical and physical surface barriers – is always prepared. The second line of defense is internal cellular and chemical defenses that become active if the surface barriers are penetrated. The first and second lines of defense involve nonspecific mechanisms that are effective against any foreign organisms or substances. The third line of defense is the immune system, which destroys specific targets, usually disease-causing organisms, and remembers those targets to mount a quick response if that target enters the body again. Thus, the immune system is a specific mechanism of defense. (What happens if immune system malfunction?)