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Skin is an external cover of the organism. The total area of skin of the adult person is about 2 meters, skin weight is 5 kg. Skin is the largest organ of the human body.
The skin and its accessory structures make up the integumentary system, which provides the body with overall protection. The skin is made of multiple layers of cells and tissues, which are held to underlying structures by connective tissue.The deeper layer of skin is well vascularized (has numerous blood vessels). It also has numerous sensory, and autonomic and sympathetic nerve fibers ensuring communication to and from the brain.
Epidermis is avascular tissue which consists of several layers of flattened cells. Dead keratinocytes are replaced by division (mitosis) of the basal cells (regeneration). The horny cells are nourished by diffusion. This skin layer
contains pigment cells called melanocytes, which have a defensive purpose, and nerve cells with a hormonal function (Merkel`s cells).
Dermis is elastic connective tissue located below the epidermis mainly consist of collagen fibers, connective tissue cells (fibroblasts), immunologi-cally active phagocytes (macrophages) and cells which mediate allergic and inflammatory reactions. This skin layer contains blood and lymph vessels as well as sense receptors. The sweet glands produce an acidic secretion (lactic acid) as an acidic protective coat (pH 5,7). This inhibits bacterial growth on the skin.
Hypoderm presents it a roughen network from thick bunch of collagen fibers, their loops are filled fatty with segments. Fatty spared are stored in under skin cellular tissue. The most developed parts of hypoderm are on belly, buttock and palms.
Horny layer is uppermost skin layer consists of layers of the denucleated remains of epithelial cells which are backed into horny plates of keratin. These are shed as scales (6-14 g daily). The horny layer functions as a barrier which provides mechanical and chemical protection. Depending on wear and tear, it between 0, 02 and 0, 50 mm thick.