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Intro to Anatomy 7: The Integumentary System
Intro to Anatomy 7: The Integumentary System
The Lone Ranger
Published by The Lone Ranger
Default Integumentary System Disorders

Integumentary System Disorders:
Disorders Due to Trauma:
A localized shedding of epithelial tissue is known as an ulcer. If blood flow in the dermis is interrupted, epidermal cells may die from lack of nutrients. Pressure on the skin can force blood out of the dermal blood vessels, as you can easily see for yourself if you have fair skin. Press down hard on the back of your hand, where the skin is fairly thin, then quickly release the pressure. You’ll be able to see that the skin has gone white from blood being forced out of it, then it reddens as blood flows back into it.

The same sort of thing happens if you lie in bed in the same position for long enough. Where there’s sufficient pressure on the skin, blood will be forced out, and if this happens for a long-enough time, epidermal cells in the affected area will begin to die and slough off. This is what causes decubitis ulcers (bedsores) in bedridden persons who aren’t moved often enough or given massages to stimulate cutaneous blood flow.
Disorders Due to Infection:
Most teens or ex-teens are familiar with acne vulgaris. This occurs when the ducts of sebaceous glands become blocked and inflamed. Bacterial infection causes accumulation of pus, and a pimple results. The sebaceous glands become more active when testosterone levels rise and thus more likely to become clogged by their secretions, which is why acne tends to afflict people when they reach puberty. Incidentally, there’s no convincing evidence that eating chocolate, french fries, or sugar in any way contributes to acne. People are variable, however, and your diet certainly affects your overall health; with that in mind, it’s possible (but by no means demonstrated) that certain foods make sensitive individuals more prone to developing acne.

Folliculitis is inflammation of hair follicles. If hair follicles are damaged by friction from clothing, shaving, or other causes, they may then become infected with bacteria. A serious infection can cause a large amount of pus to accumulate, and the result is a furuncle or boil.

Inflammation of the skin is known as dermatitis. Inflammation accompanied by edema (swelling), itching, dryness, and flaking of the skin is known as eczema. Forms of dermatitis include seborrhoeic dermatitis, which occurs when the yeast Malassezia furfur infects the skin. In most people, a yeast infection is harmless, but a severe infection causes inflammation of the skin and shedding of epidermal layers.

Contact dermatitis occurs when some sort of irritating chemical causes the skin to become inflamed. Poison ivy (Toxicodendron radicans), for example, produces a chemical known as urushiol, which causes severe itching and inflammation when it contacts the skin of a sensitive individual.

Infection of the scalp by Malassezia furfur can cause dandruff. Apparently in an attempt to cope with the infection, the body increases the rate of production of epidermal cells in an infected region. (Presumably, this is an adaptive response to try to slough off the affected tissue and get rid of the fungal infection in the process.) The result is that skin cells are shed rapidly and in large clumps.

While fungal infection is the most common cause of dandruff, it can also be caused by an usually dry scalp or by overactive sebaceous glands. For some reason, zinc deficiency seems to make one more prone to develop dandruff.
Skin Cancers:
Exposure to ultraviolet radiation in sunlight can damage DNA in the nuclei of skin cells, causing them to become cancerous. Basal cell carcinoma occurs when cells in the stratum basale become cancerous. (Carcinoma, as you recall, is any cancer of epithelial tissue.) While it can be disfiguring, basal cell carcinoma is not generally considered life-threatening. Another common type of skin cancer is squamous cell carcinoma. Exposure to sunlight can cause it in the skin, where it usually isn’t life-threatening, but squamous cell carcinoma can affect other parts of the body where squamous epithelium is found, including the esophagus, the cervix, and the lungs. Smoking is thought to be a major trigger for these more threatening carcinomas.

Melanoma occurs when melanocytes become cancerous, and it is a life-threatening condition. Any time you exposure yourself to enough UV radiation to develop a sunburn, you’re increasing your likelihood of developing melanoma. The “ABCDE” mnemonic (Asymmetry, Border, Colorful, Diameter, Evolution) may be of help if you’re worried about the possibility of developing melanoma.

An Asymmetrical skin lesion that has no obvious cause such as an injury is cause for concern, particularly if it doesn’t appear to be healing. If the Border of the lesion is irregular, that is a cause for concern. Melanomas are usually Colorful. “Moles” that are greater than 5 millimeters in Diameter are suspicious. If a mole or lesion changes in size or shape (Evolves), that is a cause for concern.
Inherited Disorders:
Erythropoietic porphyria is an inherited condition that makes sufferers’ skins extremely sensitive to sunlight. Afflicted individuals may develop dermatitis from even a brief exposure to sunlight, and more prolonged exposure will cause blistering of the skin. Long-term exposure will cause severe pain and even death of skin tissues. There’s some suspicion that people suffering from erythropoietic porphyria helped to inspire the vampire legends.

Epidermolysis bullosa simplex is an inherited condition in which the victim cannot manufacture normal keratin. As a result, the skin is so fragile that even the slightest physical contact can cause the skin to blister or even cause the epidermis to peel away from the dermis. Severely afflicted individuals develop scar tissue over much of their body surfaces.

Ichthyosis congenita (harlequin-type ichthyosis) is a particularly horrific condition that is more or less exactly the opposite of epidermolysis bullosa simplex. In ichthyosis congenita sufferers, the epidermis produces so much keratin that the skin hardens into massive, diamond-shaped “scales” or “plates.” (The name “ichthyosis” refers to the skin looking like a fish’s scales.) Children born with this condition rarely live for more than a few days, as they’re covered in what is essentially armor plating and their movements are severely restricted. Where the skin of an unafflicted person would bend, thiers cracks, leaving them at great risk of infection. With modern treatment techniques and constant care, some “harlequin babies” have managed to survive into adolescence.

Aging and the Integumentary System:
Exposure to sunlight over a person’s lifetime causes connective tissue fibers in the skin to gradually lose their elasticity, which makes the skin stiffer and more leathery. Ultimately, those who spend lots of time in the sun will often find that their skin begins to sag and wrinkle as elastin fibers are damaged by solar radiation.

Some people have collagen injected directly into the skin to treat wrinkles caused by sun damage. This can indeed temporarily smooth wrinkled skin, but the collagen fibers don’t become incorporated into the skin tissues, so it’s only a temporary measure. Some people try smearing collagen-containing creams on their skin to achieve the same effect, but they’re just wasting their time and money; collagen is much too large a molecule to be absorbed through the skin surface.

Aside from sunlight-induced damage, the skin changes in many ways as we age. For one thing, the activity of cells in the stratum basale decreases as we age, so the epidermis grows more slowly and becomes thinner. This means that older people are more susceptible to injury and skin infections.

The number of immune-system cells (Langerhans cells) in the skin decreases as we age. This, too, makes us more vulnerable to skin infections.

Vitamin D production decreases as we age. This can cause the muscles and bones of older people to become weaker.

Melanocyte activity decreases as we age, which makes the skin become paler. Especially among caucasians, this makes older people more susceptible to sunburn.

Glandular activity decreases as we age. Decreased activity of sebaceous glands can cause drying of the skin, and decreased sudoriferous gland activity means that older people cannot shed body heat as rapidly as can younger people, which makes them vulnerable to overheating in warm environments.

The blood supply to the dermis is reduced, even as sweat gland activity decreases. Because of the reduced blood flow, the skin feels cooler, which can trigger thermoreceptors (temperature-sensitive nerve endings) in the skin, making the person feel cold, even in a warm room. But because of the reduced dermal circulation and reduced sweat gland activity, overexertion in an effort to warm up can cause dangerous overheating of the body.

Hair follicles stop functioning entirely or produce thinner hairs as we age, so the hair thins. As melanocyte activity decreases, the hairs turn to gray or even to white.

Development of the Integumentary System:
Humans, like virtually all animals, are triploblasts. What this means is that, very early in fetal development (just a few days after we’re conceived), we consist of three layers of tissues. The outermost layer of tissue is known as the ectoderm, the innermost layer is known as the endoderm, and the middle layer is known as the mesoderm.

Most of the digestive system develops from endodermal tissue, but the skin doesn’t, so we won’t consider that for now. Most of the muscles of the body develop from mesoderm; as you might imagine, this includes some of the dermal tissues. However, most integumentary tissues – including the epidermis, hair follicles, sweat glands, and sebaceous glands – develop from ectodermal tissue.

Some Concluding Thoughts:
The integumentary system forms the first line of defense against the outside world. It protects us against dehydration, abrasions, cuts, ultraviolet radiation, noxious chemicals, infectious agents, and a whole host of things that would otherwise quickly kill us. That’s a pretty big job for a membrane that’s much less than an inch thick. All in all, it does a pretty darned good job, I’d say.

If the integumentary system is the one that we present to the world, the one that makes us who we are by shaping the body itself is the Skeletal System. We’ll consider that one next.

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Ensign Steve (12-13-2008)

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