Skin is an external cover of an organism, in it distinguish three layers: epidermis, to a term and hypodermic fat cellulose. Being elastic and strong, skin protects bodies and fabrics from mechanical damages, loss of water, penetration of pathogenic microorganisms and influence of ultraviolet rays.
Instruction
1. Epidermis, an outer layer of skin, consists of a multilayered flat epithelium, on different parts of the body its thickness varies. Cells of an epithelium constantly die off and are replaced with new. In them protein a keratin which gradually forces out cytoplasm and a kernel is formed therefore the corneal layer appears.
2. Under an epithelium deeper rostkovy cylindrical living cells layer with big kernels is located. Gradually they move ahead to a surface, filling the dying-off top layers.
3. On border of epidermis and terms are the cages developing a pigment melanin. It gives to skin a certain color and protects an organism from influence of ultraviolet rays. In epidermis the sensitive nervous terminations are also located. Nails and hair are derivatives of a corneal layer.
4. The basis terms is formed by friable connecting fabric, attendees of fiber in it give to skin elasticity, durability and elasticity therefore it stretches easily and displaced. A term consists of two layers — sosochkovy and mesh.
5. In a sosochkovy layer there is a set of ledges in epidermis, in it there are also blood vessels, the terminations of nervous fibers and nervous textures. Here pain, tactile, thermal and holodovy receptors are located.
6. At a mesh layer there are sweat and sebaceous glands and also hair bags in which cavity there is a root of a hair and a hair bulb. It is braided by blood vessels and nervous fibers. Tape-like muscles are attached to a hair bag.
7. The sweat gland consists of a ferruterous tubule and a direct output channel which opens on the surface of skin. Water, mineral salts, urea, ammonia and other substances is a part of sweat. Evaporating from the surface of skin, sweat cools it. Skin participates in thermal control of an organism by means of change of diameter of blood vessels and a potovydeleniye.
8. At sebaceous glands the racemose building, they are about hair bags in which cavity their channels open. The fat secret allocated by sebaceous glands softens skin and greases hair.
9. Under dermy the hypodermic fat cellulose formed by friable connecting fabric in which fat is laid is located. This layer protects an organism from overcooling, softens bruises and also serves as reserve nutritious material. Its thickness depends on a metabolism, features of food of an organism and its way of life.