Inner core (central core) is the medulla • Consist of large cells and air spaces • Absent in fine hair – Middle layer is the cortex • Bulky layer surrounding the medulla, consists of several layers of flattened cells – Outer layer is the cuticle
Structure of a Hair Cuticle • Formed from a single layer of cells that overlap one another from below like shingles on a roof • This arrangement helps to keep neighboring hairs apart so that the hair does not mat – Hair conditioners smooth out the rough surface of the cuticle and make our hair look shiny • The most heavily keratinized part of the hair, the cuticle, provides strength and helps keep the inner layers tightly compacted • It is subjected to the most abrasion, the cuticle tends to wear away at the tip of the hair shaft, allowing the keratin fibrils in the cortex and medulla to frizz out, creating “split ends”
Structure of a Hair • Hair pigments (melanin of different colors) are made by melanocytes at the base of the hair follicle and transferred to the cortical cells • Various proportions of melanins of different colors (yellow, rust, brown, and black) combine to produce hair color from blond to pitch black – Red hair is colored by the iron-containing pigment called trichosiderin – Gray or white hair results from decreased melanin production (mediated by delayed-action genes) and from the replacement of melanin by air bubbles in the hair shaft (AIRHEAD-JOKE)
Structure of a Hair Follicle • Hair follicles fold down from the epidermis into the dermis and occasionally into the hypodermis • The deep end of a hair follicle is expanded, forming a hair bulb , which is surrounded by a knot of sensory nerve endings called a hair follicle receptor , or root hair plexus , wraps around each hair bulb, and bending the hair stimulates these endings – Consequently, our hairs act as sensitive touch receptors
Structure of a Hair Follicle • Hair papilla , a nipplelike bit of dermal tissue, protrudes into the hair bulb – Contains a knot of capillaries that supplies nutrients to the growing hair and signals it to grow • The wall of a hair follicle is composed of: – Outer connective tissue root sheath , derived from the dermis, – A thickened basement membrane called a glassy membrane , – An inner epithelial root sheath , derived mainly from an invagination of the epidermis
Structure of a Hair Follicle • Hair matrix : actively dividing area of the hair bulb that produces the hair • Associated with each hair follicle is a bundle of smooth muscle cells called an arrector pili muscle – Most hair follicles approach the skin surface at a slight angle – Arrector muscles are attached in such a way that their contraction pulls the hair follicle into an upright position and dimples the skin surface to produce goose bumps
Types and Growth of Hair • Hairs come in various sizes and shapes, but can be classified as : – Vellus : vell=wool, fleece •
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- Fall '15
- Stratum lucidum, Stratum Corneum, Skin anatomy, Eccrine sweat glands