A pore is a tiny funnel-shaped opening in the skin made of a fold in the epidermis that enters into the dermis. Human skin has millions of pores over the vast majority of the body, providing locations for hair growth, sweat and skin oil production. These, in turn, protect the body in different ways. Sweat helps to regulate temperature, oils protect the skin as does hair, which can also provide sensory input when touched.
Pores often contain hair follicles. Within the pore lies the root bulb of the hair. This is the live portion of the hair shaft that produces the keratinous cells that form the hair shaft, which grows up through the pore until the hair extends above the surface of the skin, where it helps to protect the skin. The hair shaft may be fine, as with body hair, or thicker, as with hair that grows on the scalp. Around the root is a sheath of cells that protects it. Beneath the root bulb is the dermal papilla. Within the papilla is the capillary loop that provides nutrients to the follicle.
Sebaceous glands are also found in pores. They are located along the side of the pore in an opening in the pore wall. These glands appear as tiny bundled tubes with one or two small sacs that have smaller pockets within them, called alveoli. These glands produce an oily substance called sebum, which lubricates hair and softens skin tissue.
As part of the body's means of controlling its internal temperature, pores also contain sweat glands. These glands produce sweat, a watery substance containing urea, fatty acids and salt. As sweat is produced, it wells up in the pores and forms on the body, where it evaporates, producing a temperature differential that helps to cool the body.
In pores that contain hair follicles is a muscle known as the arrector pili. Composed of smooth muscle fibers, the arrector pili is connected to the side of the pore opening and extends upward and outward to join the upper layer of the dermis. These tiny muscles contract in response to emotions or cold, producing the uneven surface known as goose bumps.
Each pore has nerve endings that provide the arrector pili muscles, glands and hair follicles with impulses that control their behavior. Other nerves provide sensory feedback when hairs are touched.
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