Defenses against infection

[Jason Yan]

Natural barriers and the immune system defend the body against organisms that can cause infection. (See also Lines of Defense.)
Natural barriers include the skin, mucous membranes, tears, earwax, mucus, and stomach acid. Also, the normal flow of urine washes out microorganisms that enter the urinary tract.
The immune system uses white blood cells and antibodies to identify and eliminate organisms that get through the body’s natural barriers.
(See also Overview of Infectious Disease.)