[The body's defenses].

Abstract

The skin and mucous membranes provide first-line barriers to infection The first line of the body's defense system consists of physical and chemical obstacles to the entry of intruders. Skin: a toughened barrier. Secretions: 1. Secretions from sebaceous and sweat glands give the skin a pH of 3 ~ 5. 2. Lysozyme, one of glycosidases presented in tears, saliva, and perspiration, can digest the cell walls of many bacteria. 3. Gastric juice: pH < 2 Mucus coated the epithelium of the respiratory, digestive, and genitourinary tracts can trap microbes and other particles.