Accessory Structures of the Skin: Hair and Hair Follicles

Hairs are cylindrical and flexible cellular structures present on the skin.

The visible part of hair seen on the skin surface is its shaft, while its root is below the epidermis.

A transverse section of hair root or shaft mainly shows three concentric layers. The central core — medulla — consists of large irregular cells. The intermediate layer — the cortex—has several layers of elongated cells. The outermost layer — the cuticle — has a single layer of heavily keratinized flat cells.

The hair root is surrounded by the hair follicle, which is made up of epidermal cells and the cellular matrix.

The base of each follicle has a hair bulb wrapped by sensory nerve endings called hair follicle receptors.

In a longitudinal section, the hair bulb shows all the layers of the hair root and the hair follicle.

Deep into the hair bulb is the nipple-shaped hair papilla, whose capillaries nourish the hair.

Above the papilla lies the hair matrix — the germinal cells — responsible for the formation and growth of new hair.