In science class, a group of sixth graders are "freaked out" when they learn that nails grow continuously and are the end product of which of the following components?
A) Hypertrophy of arrector pili muscle
B) Anagen follicles
C) Telogen phase
D) Dead cells pushed outward from the nail matrix
Ans: D
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Like hair, nails are the end product of dead matrix cells that are pushed outward from the nail matrix. Unlike hair, nails grow continuously rather than cyclically. The arrector pili muscle, located under the sebaceous gland, provides a thermoregulatory function by contracting to cause goose bumps. Anagen hair has long inner roots and outer root sheaths, is deeply rooted in the dermis, is difficult to detach, and does not come out with regular brushing. Telogen hair has short, white, club-shaped roots. With formation of new anagen hair below the root, the developing follicle will eventually replace the telogen hair, leading to the shedding of approximately 50 to 100 hairs a day.
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