The hairs are flexible, horny threads developed form the epidermis. They are placed in deep narrow epidermal pits, which traverse the dermis to varying depths, and usually extend into the subcutaneous tissue. Each hair consists of a shaft which projects above the surface and a root embedded within the skin.
At the root presents a knob-like expansion, the hair-bulb, which is in close association on its under surface with a conical elevation of connective tissue (form dermis) known as the papilla of the hair. Enclosing the hair root is the hair follicle ;which consists of an epidermal and dermal parts.
Structure of hair
- The hair is composed entirely of epithelial cells, which are arranged in three definite layers.
- Medulla
- Cortex
- Cuticle.
- Medulla
- It forms the central axis of hair and consists of two or three layers of cells which vary in appearance in different parts of the hair. In the root, cells are cuboidal with rounded nuclei.
- In the shaft the cells are cornified and shrunken and the nuclei are rudimentary or absent. The intercellular spaces are usually filled with air.
- The medulla is absent from the finer, shorter hairs (lanugo) and is also absent in the hairs of scalp. If often does not extend the whole length of the hair.
- Cortex
- Makes up the main bulk of the hair and consists of the several layers of cells.
- In the root, it is composed of cuboidal cells with nuclei of normal appearance, in the lower part. At higher levels the cells become progressively flattened and in the shaft the cells become cornified, elongated and shrunken with degenerated nuclei.
- In coloured hair, pigment granules are found in and between the cells. Air accumulating in the intercellular spaces also modifies the hair colour.
- Cuticle
- It is exceedingly thin and is composed of a single layer of clear cells.
- In the deeper part of the root, the cuticular cells are nucleated but in the upper part of the root and on the shaft, the cuticular cells are clear, scale like and non-nucleated.
- The cells overlap giving the surface of the hair a serrated appearance.
