Biology 1201A Lecture Notes - Lecture 44: Apocrine, Vestigiality, Antibody

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Nails and hair are part of our appendages, the second component of the integument. The nail root is attached to the epidermis. Cells emerge from the stratum basale and other layers of the epidermis and extend to form the nail. The nail is therefore considered a part of the epidermis. It is made up of keratin packed into dead cells. The fingernails grow 4x faster than the toenails. Hair grows from the dermis, the middle layer between the epidermis and the hypodermis. The dermis has two layers (papillary and reticular layer). The follicle originates in the reticular dermis, and the shaft of the hair emerges outwards through the other layers. The hair also is composed of keratin. There is a band of muscle in the papillary dermis called the arrector pili muscle, a smooth muscle which causes hair to stand on end when it contracts.

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