Immunity is divided into two categories: innate immunity in which physical barriers are used to protect the body, and acquired immunity where specialized cells found in the tissues of the body protect it from pathogens (disease-causing organisms)
Physical barriers or mechanisms which protect the body include also chemical substances which help increase the body's protection from pathogens. Examples are:
1. The intact skin. Skin is made up of keratin in its outermost layer . Keratin makes the skin very tough and resistant. Pathogens usually cannot penetrate the skin to harm us, unless the skin gets broken.
2. The mucus membranes. These are thin membranes that form a protective lining inside many organs and parts of the body such as the trachea. Mucus produced by these membranes trap bacteria and harmful particles which are then expelled from the body.
3. Tears. Tears from our eyes contain a chemical substance called lysozyme which can kill bacteria.
Acquired immunity helps protect our bodies by use of specific biological actions These include:
1. Antibodies. Antibodies are produced by special cells of the immune system T called B-cells. Antibodies fight and neutralize pathogens that have evaded the physical barriers and entered the body.
2. Phagocytes. These are special white cells called T-cells which recognize and identify pathogens in the body then kill them by engulfing them.
