The integumentary system includes the skin and the related structures that cover and protect the body. The human integumentary system is made up of the skin, which includes glands, hair, and nails. The skin protects the body, prevents water loss, regulates body temperature, and senses the external environment.

The human integumentary system serves many protective functions for the body. Keratin, an insoluble protein in the outer layer of the skin, helps prevent water loss and dehydration. Keratin also prevents excessive water loss, keeps out microorganisms that could cause illness, and protects the underlying tissues from mechanical damage. Keratin is also the major protein found in nails and hair. Pigments in the skin called melanin absorb and reflect the sun's harmful ultraviolet radiation. The skin helps to regulate the body temperature. If heat builds up in the body, sweat glands in the skin produce more sweat that evaporates and...