Tuesday, July 07, 2009

Hair follicle structure

A hair follicle is a long tube structure which penetrates deep into the skin of the scalp. The follicle is the whole structure around a hair fiber from bulb deep in the skin to the opening to the skin surface. The bulb of the hair follicle is the point from which the hair grows .There are about 100,000 hairs follicles present in an adult human scalp. The hair follicle is a separate entity within the skin,and the structure and functions of the hair follicle are based on the interaction between dermal and epidermal components.

The follicular structure of the hair can be divided into three main parts:

* Papilla

* Hair fiber

* The root sheaths

Dermal Papilla in the hair follicle structure:

The Dermal papilla (DP) is in the form of a "pear" shape in normal and healthy hair follicles. The DP comprises a ball of cells which, during the anagen phase of the hair growth cycle, signals to the epielial component of the hair follicle to produce a keratinized hair fiber and other associated products. The dermal papilla is made up of a small group of fibroblast cells which are derived from the mesoderm. The cells are held close to the base of the epidermal cells which are responsible for the production of the hair fiber and root sheaths. So the dermal papilla itself does not make a hair fiber, but it directs the rest of the hair follicle to make one.

Though both the cell types, dermal and epithelial, are held close together they are not mixed up as there is a thin layer, called the basement membrane between the cells of dermal papilla and the epidermal cells.

The dermal papilla directs the embryonic generation of a hair follicle and it continues with this instructive function throughout the life of the hair follicle.

The thickness of the hair fiber depends on the size of dermal papilla. If the dermal papilla is bigger with the accumulation of large number of cells then the hair fiber is thicker. The DP cells are active and contain a large amount of cytoplasm when the hair fiber is produced.

But the DP cells do not multiply or increase like that of the hair producing cells that are situated above DP. When a hair follicle is not producing a fiber the DP cells lose much of their cytoplasm and become inactive.

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