Derivatives of the skin: nails, hair

Derivatives of the skin include nails and hair.

The nails are located on the terminal phalanx of the finger and protect the tips of the fingers and toes from damage. The nails are formed by the stratum corneum of the epidermis. The nail consists of a root and a nail plate formed by dense connective tissue. There are no nerve endings and blood vessels in the nail plate, but there are many of them in the nail bed. Nails are growing constantly.

Hair – horny derivatives of the epidermis. Each hair consists of a root and a shaft. The root is located in the hair follicle, immersed in a narrow long channel – the hair follicle. A smooth muscle is attached to each hair, the contraction of which raises the shaft. At low temperatures or when frightened, these muscles reflexively contract, and irregularities (“goose bumps”) appear on the surface of the skin.

Hair grows due to cell division of the hair follicle. The hair shafts are constantly lubricated with sebum, which is secreted by the sebaceous glands.

Hair color is determined by the amount of melanin it contains. When the pigment disappears, the hair turns gray.

In mammals, hair plays an important role in thermal insulation. In humans, the hairline is rare and does not really matter.