What about healthy skin
What about a healthy skin:
Skin is an organ, since it is composed of different tissues, but is unusual in that it is widely-spread and covers the whole body surface; it even continues into several body openings. Mammalian skin is composed of two main layers – superficial epidermis and deeper dermis.
Regulation of body temperature (maintenance of the warm-blooded state)
The chemical reactions taking place in all the cells of the body produce small quantities of heat. Heat is lost when any material is passed out of the body, e.g. during egestion and excretion, but the greatest heat loss is under the direct control of the brain and takes place from the skin. Although heat can be lost from a surface by conduction, convection and radiation, the last two of these are most important in the skin.
1. The skin temperature regulators are:
(a) The blood vessels:
In the extremities of the body, e.g. ear lobes and fingers, very low temperatures may cause frost-bite; under such conditions, to prevent damage the superficial skin capillaries may dilate so that the blood warms these parts – but in time the animal will have lost too much heat and will die of ‘exposure’
(b) The sweat glands
Some mammals, e.g. dogs, have very few sweat glands, and they lose heat by evaporating saliva from their tongues.
(c) The hairs
The mechanisms of temperature control in mammals (and birds) provide examples of homeostasis, i.e. automatic self-regulation within the organisms. (In birds features are used in a similar way to hairs to provide insulation). The adipose tissue of mammals gives additional heat insulation; mammals such as pigs have thick fat deposits, and in whales and seals the adipose tissue is very thick, forming ‘blubber’. In other mammals, adipose tissue is built up in autumn to prepare for severe cold.
The sweat glands extract water containing dissolved salts and a trace of urea from the bloodstream. This ‘sweat’ flows up the duct, overflows the skin surface, and is periodically washed away.
The dead horny layer is tough, impervious and inert; it provides protection against entry of bacteria (which can enter only through hair follicles and sweat glands or where skin has been frictional damage. As a consequence, even in a newly-born infant, this layer is thickest where there is greatest friction; e.g. palms and soles. The adipose tissue acts as a cushion and assists in protecting more delicate tissues under the skin from knocks and blows.
Oil from the sebaceous glands maintains the hair shaft in good condition by making it supple and less liable to break; it also water-proofs the skin and destroys certain bacteria.
The skin gives protection from radiation. Cells below the epidermis produce a brown pigment in response to excessive exposure and this acts as a barrier to the sun’s rays – hence the skin ‘goes brown’. Fair-skinned people produce less of the pigment and are more likely to blister as a result of skin damage; others produce the pigment only in small isolated patches in the skin and become ‘freckled’ when exposed to the sun.
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4. Reception of stimuli
5. Vitamin D production
When ultra-violet rays, for example from sunlight, penetrate the skin they react with fatty substances called sterols, in the dermis. These become converted into vitamin D. In this way a proportion of the nutritional requirement of this vitamin is made naturally by the body except in industrial areas where the ultra-violet light is filtered out by smoke in the atmosphere.
6. Fat Storage
In addition to its use as protective cushion and heat insulator, skin adipose tissue provides a site for the storage of fat. When needed, this food reserve is mobilized and distributed around the body in the bloodstream.