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5. The skin and mucous membranes act as barriers against pathogens by preventing pathogens from entering the body.
a) The skin is tough and acts as a wall that blocks passage into the body.
b) Sebaceous glands in the skin secrete lactic acid and fatty acids that make the skin acidic and prevent growth of many bacteria.
c) Mucous membranes contain the enzyme lysozyme that destroy bacteria.
d) Mucous membranes form a layer that physically blocks passage of pathogens into the cells lining the respiratory and digestive tracts.
e) Mucous membranes trap and flush pathogens away (by action of cilia in the respiratory tract) or as the mucous drains from the nose or is swept into the digestive tract.
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