In cold weather, blood vessels in your skin contract to reduce the amount of blood flowing near the surface of your body and so conserve your heat. This is why some people look pale or almost blue when they’re cold. In addition, the hairs on the skin stand up and this traps a layer of warm air around the body to provide extra insulation. When this happens, small bumps called goose pimples appear on the skin as tiny muscles pull the hairs upright.
protection
The skin covers virtually the entire body, providing a barrier that protects the underlying tissues from dehydration, friction, physical and chemical damage, and invasion by harmful organisms. The skin is relatively waterproof, although some moisture is absorbed when you take a bath – this causes the skin to swell, producing the wrinkling we notice after a long soak. The skin also contains sebaceous glands that produce an oily substance called sebum. This keeps the skin supple and lubricated and helps protect against moisture loss. The skin still loses some moisture, however, especially in the dry atmosphere of a modern centrally heated home or office, which is why you should apply moisturizer regularly to keep the skin supple. Sweat glands have an important defensive role, too. Sweat is slightly acidic and combines with sebum to produce a protective layer called the acid mantle that guards against bacteria and fungi. Sweat also contains an enzyme, lysozyme, that can destroy bacteria. In response to sunlight, some skin cells produce a dark-brown pigment, melanin, which blocks damaging ultraviolet radiation.
waste removal
Sweat glands not only help to control body temperature, they also excrete water, salts, and organic waste products in the sweat, so helping to regulate the body’s salt and water levels and remove toxic substances. Regular exercise increases perspiration and so helps to flush out these toxins and prevent a harmful build-up.
environmental monitor
The skin is not only a barrier but also the main link between the body and the outside world, so its ability to monitor environmental conditions is of great importance. The skin houses nerve endings and receptors that detect stimuli related to temperature, touch, pressure, and damage. These nerve endings trigger impulses that travel to the central nervous system (CNS) to keep the brain informed about your surroundings, so you can make the appropriate response, such as pulling your hand away from a hot object. The connections between the skin and the nervous system are especially important during a massage. Even the lightest of touches is registered by the brain and has a direct and immediate influence on your state of mind and emotions; a pampering touch has a calming, soothing effect, while a firmer massage will leave you stimulated and invigorated.
production of vitamin d
Vitamin D is obtained from some foods, such as meat and fish, and is also formed in the body by the action of sunlight on the skin. This vitamin aids the absorption of calcium from the gut and so is needed for healthy teeth, bones, and nerves. Although you must protect the skin from the damaging effects of excessive ultraviolet radiation (see Chapter 8), regular moderate exposure to sunshine is vital to ensure an adequate intake of vitamin D.
skin structure
Bearing in mind just how important the skin is, it should come as no surprise to learn that this organ is not a shapeless mass of cells but has a complicated structure. The skin consists of two main layers; the outer one is the epidermis and the inner one is the dermis. The main function of the epidermis is to form a tough barrier against the outside world, while the dermis is a soft, thick cushion of connective tissue that lies directly below the epidermis and largely determines the way the skin looks. Both layers are constantly repairing and renewing themselves, but the dermis does so more slowly than the epidermis. Under the dermis is a layer of fat cells, known as adipose tissue or subcutaneous (below the skin) fat, which provides insulation and protective padding as well as a store of energy.
Just as the thickness of the skin varies slightly throughout the body, so does the structure. For example, you do not find hairs on the palms of the hands or the soles of the feet. Generally, though, the skin is pretty similar all over the body. If you examine the skin in more detail you can see what an amazing job it does.
The epidermis
The epidermis is sub-divided into four distinct layers: the basal, spinous, granular, and cornified layers.
Basal layer: Cells here are attached to the basement membrane, which separates the epidermis from the dermis. Basal cells continually divide and grow to produce new cells that gradually move up through the epidermal layers to the surface. The basal layer also contains special cells, called melanocytes, that produce the pigment melanin. Melanin not only acts as a sunscreen against ultraviolet light but it also determines normal skin color, being naturally more prevalent in darker-skinned people.
Spinous layer: Here, cells rising up from the basal layer start to flatten out and produce a tough protein, keratin, to protect the body from harm.
Granular layer: In this layer, the still-living cells continue to flatten and fill with keratin but then gradually lose their nuclei to become dead cells.
Cornified layer: This is the outermost layer of the epidermis where the scale-like cells are made up almost entirely of keratin. These cells are all dead and are constantly being worn away and replaced by cells from below.
The dermis
The dermis is thicker than the epidermis. It consists mainly of connective tissue, which is made up of fibers of the proteins collagen and elastin and a non-fibrous gelatin-like material called ground substance or extracellular matrix (ECM) that fills spaces between the fibers. Moving through the matrix and among the fibers are fibroblast cells that manufacture the protein fibers and weave them together to form a web-like structure. These fibers often occur in bundles, made up of many fibrils lying parallel to one another, and they are very strong. They are found in all types of connective tissue such as bone, cartilage, tendon, and ligament.
The dermis contains blood vessels, which supply oxygen and nutrients to the skin and remove waste products, as well as special skin structures such as sensory receptors, nerve endings, sweat glands, and hair follicles – the deep pits that house the hairs. Each hair grows from the papilla, an area at the bottom of the follicle. Like skin, hair is made up mostly of keratin and is dead, except at its base, where new hair is constantly being formed. Each hair grows for about four years and then falls out and a new period of hair growth begins. Each follicle is surrounded by nerve endings that respond to the movement of the hair and can detect, for example, a light touch or a gentle breeze.
why does your skin age?
As we have already said, the dermis is mainly comprised of connective tissue so, to understand what happens to our skin as we get older, we need to look at this complex material in more detail. Connective tissue gives protection and support and is the most widely distributed material in the body. Under a microscope, the connective tissue of the dermis looks like a loose tangle of fibers. The main fibers are made up of the structural protein collagen and have great strength and suppleness. Collagen is the most abundant protein in the body and makes up about 70 percent of connective tissue. Collagen fibers are very tough and highly resistant to pulling forces although they do allow plenty of flexibility in the tissue.
Mixed up with the bundles of collagen fibers are thinner, more elastic fibers formed from a protein called elastin that increases the strength and flexibility of the