The skin is the outer layer of vertebrate animals. Its major functions are protection, temperature regulation and to act as a sense organ.
Two major layers of the skin:
The epidermis is the outer renewable layer of the skin. As it wears away at the surface it grows at the base.
Malphian Layer: This is the base layer, which is constantly producing new cells by mitosis. The new cells are pushed towards the surface. The dark pigment melanin is produced here.
Granular Layer: The protein keratin accumulates in the cells giving them a granular appearance. The cells finally die.
Cornified Layer: This is the surface layer of dead keratinised cells, which is constantly being eroded.
The dermis is the inner layer of the skin, above it is the epidermis and below it is adipose tissue.
Many different structures are present in the dermis - hair follicles, sebaceous glands, sweat glands, blood vessels, sensory nerve endings all of which are embedded in a dense matrix of connective tissue.
Functions of the Skin and Related Structures:
* Prevent excessive loss of water - the cornified layer of the epidermis is waterproof.
* Prevents the entry of pathogens the cornfield layer is made of dead cells.
* Sebum from the sebaceous glands contains anti-microbial chemicals.
* ‘Sebum oil’ keeps the skin intact preventing it from ‘cracking’.
* Melanin gives protection against the damaging UV rays of sunlight.
* The dermis and adipose tissue protect against mechanical injury.
Temperature Regulation - Maintains blood at 37oC
Threat of Temperature Rise - Increases heat loss.
* Sweat glands secrete water onto the skin surface. Evaporation of water removes heat from the body.
* Arterioles dilate increasing blood flow through the capillaries close to the skin’s surface.
* The hair erector muscles relax, the hair lies flatter reducing the depth of insulation.
The skin contains receptors for touch, pressure, pain, temperature rise and temperature decrease. The skin supplies information about a variety of external environment conditions.
Vitamin D Production: When ultraviolet light penetrates the skin converting a chemical in the blood to vitamin D. As a result vitamin D is often called the ‘sunshine vitamin’.
Excretion: The skin has about 2.5 million sweat glands. Sweat is a dilute solution of water, sodium chloride, urea, ammonia, uric acid and lactic acid. Urea, ammonia and uric acid are nitrogenous wastes.
Energy Storage: There is a layer of fat storage adipose tissue below the dermis of the skin. Fat is also a poor conductor of heat and so the skin acts as a heat insulator. This fat layer also acts as a shock absorber protecting against mechanical damage.
Many of the functions of the skin play an important role in maintaining the internal environment of the body in a constant suitable condition for efficient metabolism temperature control, protection against pathogens, vitamin D formation, excretion and role in response to changes in environmental conditions.