Monday, December 22, 2008
WHY DON’T WE HAVE HAIR ON OUR PALMS?
In humans hair is present in the skin of nearly every part of the body excepting the palms of hands, the soles of the feet, the flexor surface of the digits. The structural components of the skin alone decide the generation of the appendages of the skin. Structurally the skin has two layers: the epidermis and dermis. Among these two layers, the epidermis has a high capacity for regeneration after damage. It continually replaces the outer dead cells and also generates the appendages of the skin, like hairs, nails, sweat and sebaceous glands. In the two parts of the hair, namely the root and shaft, the root is the structure which emerges first during development and is called the hair follicle. It is set in between of the epidermis and the superficial part of the dermis. Each hair follicle commences on the surface of the skin with a funnel shaped opening. From this opening the follicle passes inwards in an oblique or curved direction. At the deep end of each hair follicle there is a small conical vascular eminence called papilla, which is continuous with the dermal layer of the skin. The capillaries of the papilla provide nutrients to the hair. When any one of the layers of epidermis and dermis gets abnormal development it affects the formation of the hair follicle and also becomes an unfit layer to support the hair. For example, in the skin of palm and soles the stratum cornium of the keratinization of epidermis and reticular layer of dermis are comparatively thicker than in the skin of other parts of our body. Such a thick keratinization zone will not allow the formation of hair follicles and the thick dermis is not the ideal structure to support the germinal matrix of the hair follicles. That is why hairs do not grow on our palm of the hands and the soles of the feet.