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Anatomy Of Body Hair


Body Hair

Although physiological functions of body hair are very important, except for eyebrows and eyelashes, which act as receptors for touching sense, they have no vital functions in human beings. In human beings colors, structures,diameters and distribution of hair in the body are varied. Race and age are determining factors for certain characteristics of hair.

 

Anatomy of body hair

Human body has an average of five million body hairs. 150 thousand is on head.

There are no hair follicles on soles, palms, lips,penises or upper parts of clitoris.

Hair grows out of follicles made up of superficial epithelium folds. In the embryogenesis stage mesenchymal cells of fetal dermis gather just below the basal layer of epidermis. In this region epidermal protuberances develop into dermis. Orders of cell widen and they surround mesenchymal cells and form bulbus. Bulbus forms the inner and outer root sheath. Two protuberances are formed on one side of the follicle.

 

The lengthwise cross section of hair follicle consists of three parts:

1) Lower part:

It is the most active part of the hair follicle.

2) Middle part:

It is closely related with sense of touch due to the small nerve fibers surrounding it.

3) Upper part:

There are many dendritic cells in this part.


The lower part of the follicle consists of 4 major parts:

- Dermal hair papilla - Hair matrix - Hair (medulla, cortex, cuticle) - Inner root sheath.

Hair follicle develops through epidermal cells growing obliquely or in a twisted manner into dermis or subcutaneous tissue.  

Proliferation of germinal cells in the hair base enables formation of hair body and inner root sheath lying in the follicular channel. In the anagen phase lower part of hair follicle takes the shape of a knob and it is named “bulbus”. Bulbus is made of matrix cells and melanocytes. Small egg shaped dermal structure (dermal hair papilla) protrudes into hair bulbus. Papilla ensures and maintains the growth of hair follicles.

In people with dark hair melanin amount in the melanophage in the dermal hair papilla is in excess. Melanin is mainly found in the cortex of the hair body. Dark colored hair contains more melanosome than light colored hair.

Melanin granules determining the color of hair are secreted in anagen phase from melanocytes in the hair bulbus.

Pluripotent cells in the hair matrix enable formation of hair and its inner root sheath.Outer root sheath, on the other hand, is like a downward extension of epidermis.