THE HAIR Hair grows out of the epidermis as a keratinized filament. The origin of the hair is the hair follicle, which is located in the dermis. The hair shaft is that portion of the hair not within the follicle. Most of the shaft is visible above the surface of the skin. The root of the hair is within the follicle, ending in the hair bulb. The hair matrix involves those basal cells that continually divide in order to make the hair grow. There is a connective tissue-derived hair papilla that is enclosed within the hair bulb and that contains both nerve endings and capillaries in the dermal layer. The basal cells that make up the hair shaft divide and push cells outward in the hair root and up into the hair shaft. This causes the hair to grow. There is an inner medulla and an outer cortex, which is made from compressed, keratinized cells. The cortex is covered by the cuticle, which is a hard-packed exterior of dead keratinized cells. Figure 27 shows the basic anatomy of a hair bulb in the hair follicle:
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