Integument or skin is the outer protective layer of the body. It protects the body from in fections and maintains its shape. Skin has hairs, it is water proof.
Skin is thick and has two layers,
Epidermis and Dermis.
EPIDERMIS
It is the outer layer of the skin. It has sensory nerves which are tactile in function. It is made up of several layers. Epidermis give rise to appendages to skin viz—hairs, nails, sweat glands, sebaceous glands etc.
Epidermis has cornified and germinative zones. Cornified zone has three strata viz.
(a) Stratum Corneum : It is outer most layer. It does not allow water to enter into the body.
(b) Stratum Lucidum : It is next to outer layer. It is a barrier layer. It is two to three layers thick.
(c) Stratum Granulosum : It is outer to spiny layer. It is six to seven layers thick.
Germinative zone has two strata namely,
(a) Stratum Spinosum : It is also six to seven layer thick. Its cells are flattened.
(b) Stratum Germinativum : It has columnar cells. It is the living layer. It absorbs nutrition from the blood cells.
These are described below:
(a) Stratum Corneum : It is totally keratinised outermost layer. It makes the outerskin waterproof.
(b) Strutum Lucidum : It is next to outer most layer and is a barrier layer. It contains hard and transparent cells.
(c) Stratum Granulosum : It is outer to spiny layer and is quite thick equal to six to seven layers.
(a) Stratum Spinosum : This layer is responsible for the rigidity of the epidermis. It is also six to seven layers thick.
(b) Stratum Germinativum. It is the only living layer. It makes all cells of upper layers. It has columnor cells.
Colour of the skin : The colour of the skin is due to the fractional concentration of a dye called melanin. The colour of the skin is also affected by a pigment carotene and protein haemoglobin and oxyhaemoglobin.
Glands of Epidermis
Epidermis has the following glands—
(a) Sebaceous glands : These are oil glands and open into the hair follicle. These glands secrete sebum. This keeps skin and hair waterproof.
(b) Sweat glands : These glands open on the surface of epidermis. They are responsible for the secretion of sweat. Sweat controls body temperature. Sweat also removes excess salts from the body.
(c) Mammary glands : These are in females. These glands secrete milk for feeding the young ones.
(d) Perinaeal glands : These are near anus. The secretion of these glands has a characterstic smell.
(e) Meibomian glands : These glands are located on the margin of eyelids.
(f) Glands leis : They are found in eyelids.
(g) Glands of Moll : They are present in eye lids.
(h) Ceruminous glands : Present in auditory meatus.
DERMIS
This layer is present below the epidermis. It is tough flexible and forms the elastic covering on the body wall. This contains the hair follicle, connective tissue, unstripped muscles, nerves, fat cells, tactile corpuscles, integumentary glands etc.
It has two layers—
(1) Stratum spongiosum : This layer is present just below the epidermis and contains blood vessels, nerves and glands.
(2) Stratum compactum : It is the innermost layer of the skin and is made up of connective tissue and adipose tissue heat insulating layer over the body.
The leather is formed from dermis. The formation of leather from dermis is called tanning. Tanning is done with tannin, alum, chromium salts etc. The process in which whole skin is preserved is called taxidermy.
Campactum acts as heat insulating layer.
DERIVATIVES OF EPIDERMIS
Hair : Hair develops from stratum malpighi and is made up of two parts—is deeply situated in the dermis and is surrounded by the hair follicle.
Fine blood vessels and small nerve fibres enter the hair follicle through the root of hair. It gives the nourishment for its proper growth and function.
Colour of hair is due to melanin pigment. When the melanin formation stops, there is accumulation of air bubble in the cortex of hair. Thus hair reflects light and make them white.
Hard derivatives of skin : Claws, nails, horns and hooves are keratinised structure derived from epidermis.
Functions of skin :
1. Skin maintains the shape of the body.
2. It provides the protection to the body form the mechanical injuries.
3. Protects against bacterical infections.
4. Acts as a store house of fats.
5. Prevents evaporation of body water.
6. It conserves heat.
7. It regulates the body temperature.
8. It is a very important sensory organ.
9. It excretes waste materials of the body in the form of sweat.
10. It produces oil and milk.
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