Architecture

How Do Nutrients Reach The Epidermis, The Layers Of The Skin

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Feel the Burn

The person in Figure (PageIndex{1}) is no doubt feeling the burn — sunburn that is. Sunburn occurs when the outer layer of the skin is damaged by UV light from the sun or tanning lamps. Some people deliberately allow UV light to burn their skin because after the redness subsides, they are left with a tan. A tan may look healthy, but it is actually a sign of skin damage. People who experience one or more serious sunburns are significantly more likely to develop skin cancer. Natural pigment molecules in the skin help protect it from UV light damage. These pigment molecules are found in the layer of the skin called the epidermis.

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Protection from Pathogens

When pathogens such as viruses and bacteria try to enter the body, it is virtually impossible for them to enter through intact epidermal layers. Generally, pathogens can enter the skin only if the epidermis has been breached, for example by a cut, puncture, or scrape in Figure (PageIndex{3}). That’s why it is important to clean and cover even a minor wound in the epidermis. This helps ensure that pathogens do not use the wound to enter the body. Protection from pathogens is also provided by conditions at or near the skin surface. These include relatively high acidity (pH of about 5.0), low amounts of water, the presence of antimicrobial substances produced by epidermal cells, and Langerhans cells, which phagocytize bacteria or other pathogens.

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Glands

Glands in the reticular layer of the dermis include sweat glands and sebaceous (oil) glands. Both are exocrine glands, which are glands that release their secretions through ducts to nearby body surfaces. The diagram below shows these glands and also several other structures in the dermis.

Sweat glands produce the fluid called sweat, which contains mainly water and salts. The glands have ducts that carry the sweat to hair follicles or to the surface of the skin. There are two different types of sweat glands: eccrine glands and apocrine glands.

Eccrine sweat glands occur in the skin all over the body. Their ducts empty through tiny openings called pores onto the skin surface. These sweat glands are involved in temperature regulation. Apocrine sweat glands are larger than eccrine glands and occur only in the skin of the armpits and groin. The ducts of apocrine glands empty into hair follicles, and then the sweat travels along hairs to reach the surface. Apocrine glands are inactive until puberty, at which point they start producing an oily sweat that is consumed by bacteria living on the skin. The digestion of apocrine sweat by bacteria is the cause of body odor.

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Sebaceous glands are exocrine glands that produce a thick, fatty substance called sebum. Sebum is secreted into hair follicles and makes its way to the skin surface along with hairs. It waterproofs the hair and skin and helps prevent them from drying out. Sebum also has antibacterial properties, so it inhibits the growth of microorganisms on the skin. Sebaceous glands are found in every part of the skin except for the palms of the hands and soles of the feet where hair does not grow.

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