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.