The term “soft tissue injury” is often used to describe an injury to the skin and/or mucous membranes.

a. Skin.

The skin is the body’s largest organ. The skin is watertight and bacteria cannot penetrate it unless there is a break (open wound) in the skin. The skin helps to regulate body temperature. The body is cooled in warm weather by the evaporation of perspiration and the dilation of blood vessels in the skin. In winter, the constriction of blood vessels in the skin helps to retain body heat.

Specialized nerve endings transmit sensations such as heat, cold, pressure, pain, and position of the body in space. The three layers of the skin (epidermis, dermis, and subcutaneous layer) were described previously in paragraph 6-3a.

b. Mucous Membranes.

Mucous membranes line all body openings (orifices) such as the nose, mouth, anus, and vagina. The mucous membranes perform the same basic function of protecting the body from invasion by bacteria that the skin performs. Mucous membranes secrete a watery substance called mucus that keeps the orifices lubricated.