Our skin is one of the largest single organs, which weighs nearly 16% of total body weight. The skin is nearly 2 square meter i.e.20 square feet in area. It is a multipurpose organ which - covers, protects, and prevents desiccation as also disallows microbes from entering in to our bodies.
The skin helps to regulate body temperature and excretes waste material. The photochemical action in skin produces vitamin D. (Vitamin D-3 i.e. Cholecalciferol). Through the extensive network of sensory receptors in skin we get sensations of touch, pressure, temperature (both rise and fall) and pain. The skin with its colored pigment, melanin, protects us from mechanical shocks, chemicals harmful to us and from the Ultra-violet radiation. It can stretch and grow and envelopes additional mass of body as and when required - such as during pregnancy or development of edema.
And such a virtuous cover keeps on regenerating all the time!
The skin of land-dwelling i.e. terrestrial animals is associated with such structures as scales, claws, shells, horns, hooves, feathers, nails, and hair. Mammalian skin has many glands associated with it like the ceruminous (cera = wax. So, wax producing) glands, sebaceous glands, mammary glands, sweat glands, meibomian glands.
The skin is thick and glabrous i.e. smooth in some parts of body such as, the sole of foot and palm of hand. It is thin and with hair on rest of the body. Above the eyes it is thin and without hair as also on lips.
The thickness and thinness is generally related to the thickness of the outer and upper layer of skin called the epidermis. There are two main layers of the skin viz. epidermis and dermis.
The epidermis has no blood vessels in it and is made of five layers. These five layers (strata) from inside to outside are – (1) Stratum basale (2) Stratum spinosum (3) Stratum granulosum (4) Stratum lucidum (5) Stratum corneum.
Let us get a brief idea of each one of these layers now. (1) Stratum basale – Also called stratum germinativum, this layer shows continuously dividing cells. This layer only one cell in thickness and its cells are attached to each other tightly with the help of tiny tenacious threads called desmosomes. The entire layer regenerates in maximum thirty days time. ( People with psoriasis have such intense mitotic activity in this layer that in 7 days the entire layer replaces itself) The layer contains many granules of a substance called keratohyaline.
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