Hair and nails
At first sight, hair and nails grow at us more for appearance, than for advantage, but strong nails allowed our primitive ancestors to pick out edible korenja, and the dense vegetation on a body and a head protected from a bad weather.
For thousand years of use of instruments of labour, lives in cosy houses and clothes carrying our external shape became much more attractive. However and today the scalp in bolshem or smaller quantity is present at us almost on all body, we till now vypol njaem by means of nails a jobbing (for example, we we remove konfetnye wrappers), and hair in some measure protect a head from a cold or the scorching sun.
Hair and nails consist basically from keratina (one of fiber kinds), forming also an external layer of a skin. From keratina horns and hoofs of animals consist a wool. Hair and nails are deprived almost any sensitivity. But if to pull for hair or a nail, you chuvstvi telnaja a skin immediately will let to you about it know.
As hair grow
Hair are so inherent in our nature, what even in pre-natal development the body of the baby is covered by the most thin scalp (lanugo). Shortly before a birth it is replaced by a so-called first-born down, and only in process of growth on a head and a body of the child gradually there are usual hair.
On a head at the adult person grows about 120 000 hair. Each hair on a head and a body grows from own root named skin sosochkom. The basis the root enters into a tiny sack in a skin, or a follicle where receives a food from blood vessels. In each follicle there is a sebaceous gland allocating microscopic quantity of oily substance, called by skin fat. This substance greases hair and shine adds to them. Besides, the follicle is supplied by the tiny muscle which Latin name means "яюфэшьр=хыі тюыюё". From a cold or ispu hectare these muscles are reduced, and hair rise on end. Here just it is time to recollect times when our ancestors have been entirely covered by hair, and the tousled wool helped them to be warmed or gave more a menacing look. Birds too surround themselves with a warming air cushion, having ruffled up on a strong frost, and at cats at the sight of a dog the wool rises on end, helping them to seem more and more terribly. At reduction of these muscles at us on a skin act small bugorki - all the acquaintance "уѕёшэр ъюцр".
Process of growth of hair consists of several phases. It begins with an active phase during which hair constantly grows from a root. Approximately in 4 years it is replaced by a rest phase when completely evolved hair gradually istonchaetsja and drops out. During the third phase an empty follicle some months have a rest, then process renews. Hair on a head grow with a speed of 1,25 sm a month with insignificant deviations at different people. By itself, on a head they grow much more long, than on other sites of a body. On the average the person loses for days from 40 to 100 hair which have become obsolete the term, but instead of them in had a rest f ollikulah the new always grow. Owing to hormonal reorganisation at puberty at boys and girls hair in the field of armpits and on lobke grow, and a little later at young men hair on the person start to grow and is frequent on a breast and a back. This type of a scalp is included into number of secondary sexual signs.
Types and forms of hair
The Visible part of hair represents the core of the become horny fabric consisting of albuminous chains linked among themselves. Only growing part of hair hidden in skin sosochke is rather live. Under a microscope it is well visible that the surface of a hair core is covered cheshujkami, as a skin at reptiles or the bird's pads. The same kind has also a nail surface. Depending on the form of a hair core hair happen direct, wavy or curly. At a straight hair the core round, at wavy or curly - oval, and at hair of the African type - is bent on a spiral.
the Hair colour
Besides the cages developing keratin of which the hair core consists, in follicles there are also other cages - melanotsity. The pigment developed by them melanin gives to hair colour. The more melanin, the hair (thanks to melanin the light skin becomes covered by a deep ten on the sun) are more dark.
In process of ageing of the person in folliku lah it is developed ever less melanin, and hair gradually grow grey. The type and a hair colour, and also age with which begins posedenie, is defined by hereditary factors.
The Nail represents a protective horn plate and grows from a root which is looking like the small platen on a game chikah of fingers of hands and feet. Site of a nail directly adjoining to a root, or lunka, a bit thicker than other plate because of what it seems white. Other nail is almost transparent, and under it the skin appears through. Along the edges it is protected by a layer of the become horny skin (kutikuly), a little utolshchennym around lunki.