Anatomy
1. Hair is composed of columns of dead, keratinized cells bonded together by extracellular proteins.
Shaft: is the superficial portion of the hair which projects from the skin.
Root: is the portion of hair deep to the shaft that penetrates into the dermis, and sometimes into the subcutaneous layer.
The shaft and the root both consist of three concentric layers of cells :
1. Cuticle - The outermost layer is a single layer of flat keratinized cells that overlap one another much like the scales of a fish.
2. Cortex - a middle layer of densely packed keratinized cells.
3. Medulla – the central medulla is a solid at the root but spacious in the shaft and consists of cuboidal cells.
Follicle: surrounding the root of the hair made up of an external root sheath and an internal root sheath together referred to as an Epithelial Root Sheath. Bulb: the base of each follicle and its surrounding dermal root sheath is an onion-shaped structure called the bulb. The bulb contains a germinal layer of cells called a Hair Matrix. The matrix is the site of cell division and is responsible for the growth of existing hairs and new hairs when old hairs are shed. Hair matrix cells also give rise to cells of the internal root sheath.
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