The skin as a boundary element
The skin protects the body against the ingress of pathogens and gaseous, liquid or solid foreign substances in the broadest sense, from mechanical injury, radiation damage, but also from fluid, electrolyte and protein losses, which take in severe burns of the skin life threatening. It is populated by bacteria and fungi, known as the resident skin flora. function as antigen presenting cells in the skin Langerhans cells.
mass transfer
over the body surface in varying degrees in different animals substances from the environment and released. These can be gaseous, liquid or solid (dissolved in an aqueous medium). The mass transfer can actively run (under energy expenditure) or passive (in the direction of an osmotic gradient).
The gases may be: the absorption of oxygen and the release of carbon dioxide (skin respiration), but also nitrogen and inert gases. Water can be absorbed serve or be discharged to the water regulation and as a transport medium for dissolved gaseous or solid substances. Dissolved substances may be salts (uptake or release), nutrients (many parasites the exclusive uptake, excretion products, but also toxic substances from the environment (such as organic lead compounds).
About the skin, the body can regulate its heat balance. overheating effect against the skin with the sweat glands. By the sweat production potential evaporation and the resulting heat is dissipated by the close under the skin running capillaries that are open to an extent (see sweating). With the help of the subcutaneous fat tissue and to a lesser extent by the heat of the hair is held back. In cold blood circulation in the skin are and subcutaneous fat only slightly, and both act by an insulator layer. The hair can take on due to the small coat of man only small isolation function. Still, one can observe the working principle of a fur garment still good. When occurring in the cold creeps directed the M
