The skin consists of three layers: the epidermis, the dermis and the subdermis. Learn about the structure and function of these layers and how they interact.
The skin protects the body from outer impacts. It also helps to keep the water and the fluids in the body from seeping out or from evaporating. The skin also helps to give the body its shape, firmness and elasticity. It helps to regulate the body temperature by means of blood flow and sweat. The skin also has aesthetic functions and provides an interface for intimacy between persons. The skin also provides the immediate immune protection against microbes.
It consists of three layers, the outer layer or epidermis, the mid layer called dermis, and the hypodermis at the bottom. The skin has pores that contain sebaceous glands, glands for substances giving scent, and contains the hair roots.
THE OUTER LAYER - EPIDERMIS
The epidermis, which is 0.05 - 1.5 mm thick, consists of several sub-layers. At the bottom there is a layer of cells called basal cells, shaped like columns. In this layer the cells constantly divide to produce new cells.
The new cells are gradually pushed towards the surface. While this happens, they get filled with the protein keratin and dry. Each of these cells will eventually get pushed all the way outward into the surface layer of the epidermis and will then be dead flakes consisting mostly of keratin. The cells that are pushed outward are distributed in three sub-layers distinguished by their development face: stratum spinosum,stratum granulosum and stratum licidum
The outermost layer of the epidermis, the stratum corneum, consists only of these flat dead flakes of keratin which once were cells pushed outward from beneath. The keratin flakes are constantly worn off by daily mechanical impacts and constantly renovated from beneath. If the skin on a body part gets subjected to hard daily impacts, the cells in the epidermis can react by an increased proliferation of cells, so that the keratin layers get thicker.
The epidermis also contains corns of the color substance melanin and cells producing this stuff, called melanocytes. The epidermis does not contain blood vessels, but get nourishment and oxygen that diffuse upward from the layer beneath. There are also cells serving the immune defense called Langerhan's cells.
THE MID LAYER - DERMIS
The dermis, of thickness 0.3 - 3.0 mm, consists of connective tissue. Important components of this layer are fibers of the elastic protein elastin, and the firmer protein collagen. There are also cells that make these fibers, fibroblasts. The fibers give the skin elasticity and also firmness. The dermis have a thin upper layer with thin collagen fibers, the papillary layer. The layer beneath, the reticular layer, is much thicker and has thick collagen fibers going parallel to the skin surface. The dermis has blood vessels, especially a dense network of very thin vessels called capillaries. The network of capillaries is especially dense just under thee epidermis in order to nourish the dermis that do not have blood vessels.
The dermis have nerves that conduct censorial impulses towards the central nervous system and nerves conducting impulses to adjust the functions or sweat glands and muscle bundles connected to the hairs. Sense of pain originates from bare nerve endings. Sense of pressure and motion in the skin originates from censorial bodies which have the nerve ending in their mid. These are especially dense just beneath the epidermis.
The dermis contains all types of immune cells and factors that protect the skin itself and the body from microbes and other hazards. There are antibodies that can fix and glue microbes, cells that make the antibodies, and cells that can eat and digest the caught intruders. Upon threats and injury the skin also reacts by swelling and by increased blood stream to make it easy for immune cells to navigate and to help to tidy up the skin tissue. These reactions are controlled by histamine and other tissue hormones secreted by certain cells in the skin, for example mast cells.
THE INNERMOST LAYER - SUBDERMIS
The subdermis consists of a connective tissue with many of the same components like the dermis, but it also have a lot of fat cells. The subdermis is variably thick depending upon how filled the fat cells are. The fat cells serve as a deposit for energy and nutrients in the form of fat. The subdermis also function as a protective pad for the deeper part of the body againstimpacts from the outside. The fat in this layer also serve as isolation against loss of heat from the body.
The subdermis have greater blood vessels that distribute blood throughout the skin and up to the dermis, and collect the blood again to send it back towards the heart and there are greater nerves with thinner branches up to the dermis.
THE PORES, HAIRS AND GLANDS
The skin has pores going from the surface to the deepest part of the dermis. The pores are actually sack-like wrappings inward from the epidermis The lining inside these pores consist therefore of epidermal cells.
The hairs grow up from the bottom part of the pores, the hair follicle, which surrounds the hair root The hair root is served by blood vessels that enter at the very bottom of the hair root and make a little loop just inside. From this loop nutrients and oxygen diffuse to other parts of the hair root. In the hair root cells divide and get filled with keratin just as in the epidermis, but the keratin flakes are used to make the hair that grow up from the pore.
There is a little muscle attached to each hair, the levator pili muscle. When the muscles contract, the hairs will rise and the skin will also get a more textural structure with a lot or small bumps. The action of the muscles are controlled by nerves in the skin and by reflexes from censorial imputs and emotions, like feeling cold or being afraid.
At the walls of the pores there are sebaceous glands that make a blending if oily and vaxy substances, called sebum. Inside these glands new cells are steadily made and these cells make sebum that gradually fill them up. At some point the cells burst so that the sebum is emptied into the pores. The sebum lubricates the hairs and will also be pushed toward the opening of the pore and also lubricate the skin.
At the pore linings there are also glands that make smelling substances, pheromones, or substances that nourish friendly bacteria that make scents and help to protect. These substances signal emotional information between persons, and stimulate psychological reactions, for example for sexual attraction. The scent from these can be perceived both consciously and subconsciously.
The cells in the pores serve as a reserve for repair of the epidermis when it is damaged. With totally damage of the outer epidermis, new epidermis will grow up from the lining of the pores and spread upon the skin surface. The deep of the pores also contain stem cells that can differentiate to other types of skin cells by skin damage.
The skin also has sweet glands opening up to the surface through small tubes. These glands are themselves shaped like a tube which is coiled up and each gland is furnished by a dense network of blood vessels. Sweat is mostly a blending of water and minerals. The sweat cools the body and the body also gets rid of wastes by means of sweating.
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Knut Holt is a business consultant and marketer interested in the health field. To read more about health topics and to find natural products for treatment of problems in the skin, muscles, joints, windpipe, stomach, nervous system, circulation and urogenital system, please see his web-site.