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Beauty-Basics.Net |
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Structure of the skinThink of skin as a three-layer sandwich. The outer horny layer, or stratum corneum, is composed of flat skeletons of cells made up of keratin protein. These overlap like scales and are glued together with lipids - the skin's natural oils. Although this layer is technically dead, its protective "armour plating" is vital to skin health. Its horny, water-resistant structure forms a barrier against moisture loss from within the skin, while repelling potentially hazardous external elements. A cocktail of friendly flora gives it anti-bacterial properties that help withstand infection. This outer layer is sealed by a membrane that lies between it and the living cells of the next layer down - the epidermis. The epidermis has two functions. It supplies the stratum corneum with cells while attracting and preserving moisture to keep the skin soft and plump. From the bottom, or basal line, of the epidermis, cells bud off, divide and migrate toward the surface, progressively maturing, ageing and flattening until they become the dead scales of the stratum corneum. In healthy skin, this cell-turnover process takes around 28 days. There are two growth spurts daily: one In the early morning and a milder phase in the early after noon, when levels of the life-giving hormone cortisol are lowest and body repairs take place. New cells arriving at the surface of the outer layer push off old skeleton cells, so the stratum corneum is constantly renewing itself. Both the stratum corneum and the epidermis are referred to as the skin's upper layers. This vital layer of the skin is relatively narrow, the deepest of the skin's layers is the the next layer down, the dermis. BENEATH THE Upper layers Directly below the basal line of the epidermis is the dermis - the skin's lowest layer. Here, parallel bundles of collagen and elastin form the supportive structure at the skin's foundation. These proteins are also responsible for the skin's firmness, plumpness and elasticity. Also running through the dermis is a network of nerves and an extremely rich system of blood vessels or capillaries. These supply cells with essential nutrients and give the skin its rosy glow. The strength and proximity to the surface of these capillaries determines how prone the skin will be to "broken veins" as it ages. Hair follicles are rooted in the dermis where they are served by nerves and blood vessels. Further up toward the basal line of the epidermis, sebaceous glands supply each hair with lubricant oil ). This oil, or sebum, works its way up the hair follicle and spills out on to the skin's surface. Composed of more than 40 acids and alcohols, sebum creates a protective film known as the skins acid mantle, which assists in the horny layer's barrier function against moisture loss and infection. To maintain its anti-bacterial, antiseptic status, the acid mantle must remain at between pH (acid balance) 4 and 6. Alkaline detergents and some cleansers disrupt this balance, leaving the skin vulnerable to dryness and possibly infection. Hyperactive sebum secretion poses problems of its own. Sweat glands (which help regulate body temperature and fluid levels, and eliminate fluid waste) originate in the dermis and end in outlets, or ducts, on the skin's surface. Sweat is one of the body's major means of temperature control: as the temperature rises more sweat is excreted to the the skin, then as the sweat droplets evaporate this has a cooling effect at the skin's surface. The other components of sweat, such as minerals, waste products and hormones, vary around the body. Sweat excreted from the underarm and groin areas are heavily laced with hormones, which give sweat (particularly after contact with the skin bacteria inhabiting these areas!) its own, distinctive, natural aroma. The dermis is also involved in another means of temperature regulation. When the body overheats, the fine capillaries near the surface of the skin dilate, increasing the blood supply. This has the effect of cooling the blood near the external surfaces of the body. When the external temperature becomes significantly cooler, the capillaries contract, drawing blood away from the cool surface of the skin and into the body's warmer core. Hence that pale face when you are uncomfortably cold. and the red face when you have been working out in the gym - it just shows your body's systems are working efficiently! Beneath the dermis lies a layer of subcutaneous fat threaded through with veins and arteries. This insulating layer preserves warmth and provides the body with fuel in "lean" times. It is more generously distributed in women and can harbour cellulite. |
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