Hair Follicle: Extends from the epidermal surface to the dermis. The deep end of the follicle is expanded forming a bulb. A knot of sensory nerve endings (root hair plexus) wraps around the bulb. Hair acts as sensitive touch receptors. Papilla is a nipple-like bit of tissue containing a knot of capillaries which protrudes into the hair bulb and supplies it with nutrients. The epithelial cells of the hair matrix (bulb) are actively mitotic germinal centers which produce the hair. As new hair cells are produced the older parts are pushed up. The cells fuse and are increasingly keratinized and they die. The hair shaft is made almost entirely of keratin. Structures associated with hair follicles: Nerve endings, Sebaceous glands, Smooth muscle structures -- arrector pili Most hair follicles approach the skin surface at a slight angle. The arrector pili attach to the follicle so that their contraction pulls the hair into an upright position, dimpling the skin surface and producing "goose bumps." The arrector pili are regulated by the nenous system.
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