Compare the anatomy distribution and physiology of

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3.Compare the anatomy, distribution and physiology of the epidermal derivatives listed below.Accessory structures of the skin – hair, skin glands, and nails.A. Hair:I.Functions of hair:a.Guards the scalp from injury and the sun’s raysb.Decreases heat loss from the scalpc.Eyebrows and eyelashes protect the eyes from foreign particlesd.Function in sensing light touch.i.Touch receptors (hair root plexuses) associated with hair follicles are activated whenever a hair is moved even slightly.II.Shaft:a.The superficial portion of the hair, which projects above the surface of the skin.III.Root:a.Is the portion of the hair deep to the shaft that penetrate into the dermis, and sometimes into the subcutaneous layer.b.Medulla, cortex, cuticle: the shaft and the root of the hair both consist of 3 concentric layers of cells; medulla, cortex, and cuticle of the hair.i.The inner medulla, which may be lacking in thinner hair, is composed of 2 or 3 rows of irregularly shaped cells that contain large amounts of pigment granules in dark hair, small amounts in grey hair, and a lack of pigments and the presence of air bubbles in white hair.ii.The middle cortexforms the major part of the shaft and consists of elongated cells.
iii.The cuticle of the hair, the outermost layer, consists of a single layer of thin, flat cells that are the most heavily keratinized.IV.Hair follicle: a.Surrounding the root of the hair is the hair follicle.b.Made up of an external root sheath and an internal root sheath, together referred to as an epithelial root sheath.i.The external root sheathis a downward continuation of the epidermis.ii.The internal root sheathis produced by the matrix and forms a cellular tubular sheath of epithelium between the external root sheath and the hair.iii.The dense dermis surrounding the hair follicle is called the dermal root sheath. V.Bulb:a.The base of each hair follicle and its surrounding dermal root sheath is an onion-shaped structure.b.This structure houses a nipple-shaped indentation, the papilla of the hair, which contains areolar connective tissue and many blood vessels that nourish the growing hair follicle.c.The bulb also contains a germinal layer of cells called the hair matrix.VI.Matrix:a.The hair matrix cells arise from the stratum basale, the site of cell division.b.Hair matrix cells are responsible for the growth of existing hairs, and they produce new hairs when old hairs are shed.c.This replacement process occurs within the same follicle. Hair matrix cells also give rise to the cells of the internal root sheath.VII.Arrector pili muscle: a.The smooth muscle is the arrector pili.b.It extends from the superficial dermis of the skin to the dermal rootsheath around the side of the hair follicle.c.In its normal position, hair emerges at 90▫ angle to the surface of the skin.i.Under physiological or emotional stress autonomic nerve endings stimulate the arrector pili muscles to contract, pulling the hair shafts perpendicular to the skin surface.
VIII.Hair root plexus:a.Surrounding each hair follicle are dendrites of neurons that form a

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