http://www.ck12.org Chapter 1. Human Biology
FIGURE 1.
Goosebumps are caused by tiny mus-
cles in the dermis that pull on hair folli-
cles, which causes the hairs to stand up
straight.Oil Glands and Sweat Glands
Glands and hair follicles open out into the epidermis, but they start in the dermis. Oil glands (Figure1.5) release,
or secrete an oily substance, calledsebum, into the hair follicle. Sebum “waterproofs” hair and the skin surface to
prevent them from drying out. It can also stop the growth of bacteria on the skin. It is odorless, but the breakdown
of sebum by bacteria can cause odors. If an oil gland becomes plugged and infected, it develops into a pimple. Up to
85% of teenagers get pimples, which usually go away by adulthood. Frequent washing can help decrease the amount
of sebum on the skin.
Sweat glands(Figure1.5) open to the skin surface through skin pores. They are found all over the body. Evaporation
of sweat from the skin surface helps to lower skin temperature. The skin also releases excess water, salts, and other
wastes in sweat.
Vocabulary
- dermis: Layer of skin directly under the epidermis; made of a tough connective tissue.
- epidermis: Outermost layer of the skin.
- integumentary system: Outer covering of your body, including skin, hair, and nails.
- melanin: Brownish pigment that gives skin and hair their color.
- perspiration: Sweat, made almost completely of water, with tiny amounts of other chemicals like ammonia,
urea, salts, and sugar. - sebum: Oily substance secreted in the skin.
- sweat gland: Small gland that secretes sweat.
Summary
- Skin serves many functions, from acting as a barrier that keeps particles and water out of the body, to helping
to cool the body. - Skin is made up of two layers, the epidermis and the dermis.