Exam 2 Review: Chapter 5: Hair and Nails
pili = hairs - An epidermal derivative produced by the hair follicle in the dermis of the skin; the cylindrical, keratinized, often pigmented protein filaments characteristically growing from the epidermis of a mammal, composed of an exposed shaft and an embedded root; they function in thermoregulation (evaporative cooling), communication, sensory reception, dry lubrication where the limbs extend from the trunk, secondary sexual characteristic, etc.; growth patterns are regulated by heredity, sex hormones, nutrition and health status.medulla - The inner core of an internal organ or body structure; e.g., the interior of the hair shaft which contains soft keratin.
cortex - The outer layer of an internal organ or body structure; e.g., the exterior of the hair shaft (which is covered by a thin layer of waterproof cuticle) which contains hard keratin and pigments.
hair follicle - The tubular infolding of the epidermis containing the root of a hair and the supporting sheath and bulb and to which are attached a sebaceous gland and an arrector pili muscle.
bulb of the hair - The lower expanded section of the root of a hair which fits like a cap over the hair papilla; it is located at the bottom of the hair follicle and it contains the cells from which the hair shaft develops.
papilla of the hair - The small nipplelike projection or protuberance of areolar connective tissue at the base of the bulb portion of the root of a hair which brings the capillary blood supply closer to the epidermal cells involved in the synthesis of the growing hair shaft.
arrector pili - The short strand of involuntary smooth muscle that extends from the side of a hair follicle on which the sebaceous gland is located to the basement membrane of the nearby epidermis; when contracted the action of the muscle causes the hair shaft to stand more erect; contraction of the muscle is stimulated by exposure to cold or as a result of emotional upsets, e.g., anger or fear.
root hair plexus - A complex sensory exteroreceptor for fine touch consisting of a network of sensory nerve endings wrapped about the bulb of each hair follicle; external movements of the hair shaft stimulate the receptor. [aka hair follicle receptor]
nails - An epidermal derivative produced at the dorsal surface of the distal phalanges (fingers and toes) which consists of a flattened plate of densely packed keratinized cells, used to improve the grasp of the fingers and to protect the tips of the digits.
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