The skin also:. Your skin takes on different thickness, color, and texture all over your body. For example, your head contains more hair follicles than anywhere else.
But the soles of your feet have none. In addition, the soles of your feet and the palms of your hands are much thicker than skin on other areas of your body. Squamous cells. Bedbugs have highly developed mouth parts that can pierce skin.
In most cases, we do not know what causes birthmarks. Most are harmless, happen by chance and are not caused by anything the mother did wrong in pregnancy. If you are bitten or stung by an insect or animal, apply first aid and seek medical treatment as soon as possible. A blister is one of the body's responses to injury or friction.
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Skip to main content. Home Skin. Skin explained. Actions for this page Listen Print. This trip takes about 2 weeks to a month.
As newer cells continue to move up, older cells near the top die and rise to the surface of your skin. What you see on your hands and everywhere else on your body are really dead skin cells. These old cells are tough and strong, just right for covering your body and protecting it. But they only stick around for a little while. Soon, they'll flake off. Though you can't see it happening, every minute of the day we lose about 30, to 40, dead skin cells off the surface of our skin.
So just in the time it took you to read this far, you've probably lost about 40, cells. That's almost 9 pounds 4 kilograms of cells every year! But don't think your skin might wear out someday. Your epidermis is always making new skin cells that rise to the top to replace the old ones.
They make a substance called melanin say: MEL-uh-nun. Melanin gives skin its color. The darker your skin is, the more melanin you have.
When you go out into the sun , these cells make extra melanin to protect you from getting burned by the sun's ultraviolet, or UV, rays.
That's why your skin gets tan if you spend a lot of time in the sun. But even though melanin is mighty, it can't shield you all by itself. You'll want to wear sunscreen and protective clothing, such as a hat, to prevent painful sunburns. Protecting your skin now also can help prevent skin cancer when you get older. The next layer down is the dermis say: DUR-mis. You can't see your dermis because it's hidden under your epidermis.
The dermis contains nerve endings, blood vessels, oil glands, and sweat glands. It also contains collagen and elastin, which are tough and stretchy. The nerve endings in your dermis tell you how things feel when you touch them.
They work with your brain and nervous system, so that your brain gets the message about what you're touching. The epidermis is composed of layers; most body parts have four layers, but those with the thickest skin have five. The layers are:.
The epidermis also contains other cell structures. Keratinocytes are formed by division in the stratum basale. As they move up through the stratum spinosum and stratum granulosum, they differentiate to form a rigid internal structure of keratin, microfilaments and microtubules keratinisation. The outer layer of the epidermis, the stratum corneum, is composed of layers of flattened dead cells corneocytes that have lost their nucleus. These cells are then shed from the skin desquamation ; this complete process takes approximately 28 days Fig 3.
Between these corneocytes there is a complex mixture of lipids and proteins Cork, ; these intercellular lipids are broken down by enzymes from keratinocytes to produce a lipid mixture of ceramides phospholipids , fatty acids and cholesterol.
The stratum corneum can be visualised as a brick wall, with the corneocytes forming the bricks and lamellar lipids forming the mortar. As corneocytes contain a water-retaining substance — a natural moisturising factor — they attract and hold water.
The high water content of the corneocytes causes them to swell, keeping the stratum corneum pliable and elastic, and preventing the formation of fissures and cracks Holden et al, ; Cork, This is an important consideration when applying topical medications to the skin. These are absorbed through the epidermal barrier into the underlying tissues and structures percutaneous absorption and transferred to the systemic circulation.
The stratum corneum regulates the amount and rate of percutaneous absorption Rudy and Parham-Vetter, One of the most important factors affecting this is skin hydration and environmental humidity.
In healthy skin with normal hydration, medication can only penetrate the stratum corneum by passing through the tight, relatively dry, lipid barrier between cells. When skin hydration is increased or the normal skin barrier is impaired as a result of skin disease, excoriations, erosions, fissuring or prematurity, percutaneous absorption will be increased Rudy and Parham-Vetter, Melanocytes are found in the stratum basale and are scattered among the keratinocytes along the basement membrane at a ratio of one melanocyte to 10 basal cells.
They produce the pigment melanin, manufactured from tyrosine, which is an amino acid, packaged into cellular vesicles called melanosomes, and transported and delivered into the cytoplasm of the keratinocytes Graham-Brown and Bourke, The main function of melanin is to absorb ultraviolet UV radiation to protect us from its harmful effects.
Skin colour is determined not by the number of melanocytes, but by the number and size of the melanosomes Gawkrodger, It is influenced by several pigments, including melanin, carotene and haemoglobin. Melanin is transferred into the keratinocytes via a melanosome; the colour of the skin therefore depends of the amount of melanin produced by melanocytes in the stratum basale and taken up by keratinocytes. Skin colour is also influenced by exposure to UV radiation, genetic factors and hormonal influences Biga et al, Langerhans cells.
These are antigen micro-organisms and foreign proteins -presenting cells found in the stratum spinosum. Merkel cells. These cells are only present in very small numbers in the stratum basale. They are closely associated with terminal filaments of cutaneous nerves and seem to have a role in sensation, especially in areas of the body such as palms, soles and genitalia Gawkrodger, ; White and Butcher, This is a narrow, undulating, multi-layered structure lying between the epidermis and dermis, which supplies cohesion between the two layers Amirlak and Shahabi, ; Graham-Brown and Bourke,
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