|Human Physiology 6/e Fox|
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Clinical Disorders of the Integumentary System
The integumentary system is useful in diagnosis because it is easily observed and often reflects events occurring in other parts of the body. For example, cyanosis, a bluish color that results from decreased blood oxygen content is an indication of impaired circulatory function or respiratory function. When red blood cells wear out, they are broken down, and part of their contents are excreted by the liver as bile pigments into the intestine. Jaundice (jaun'dis), a yellowish skin color, occurs when there are excess bile pigments in the blood. If the liver is damaged by a disease such as viral hepatitis, bile pigments are not excreted and accumulate in the blood.
Rashes and lesions in the skin can be symptomatic of problems elsewhere in the body. For example, scarlet fever results from a bacterial infection in the throat. The bacteria releases a toxin into the blood that causes the pink-red rash for which this disease was named. In allergic reactions a release of histamine into the tissues produces swelling and reddening. The development of a rash (hives) in the skin can indicate an allergy to ingested foods or drugs such as penicillin.
The condition of the skin, hair, and nails is affected by nutritional status. In vitamin A deficiency the skin produces excess keratin and assumes a characteristic sandpaper texture, whereas in iron deficiency anemia the nails lose their normal contour and become flat or concave (spoon shaped).
The hair concentrates many substances that can be detected by laboratory analysis, and comparison of a patient's hair to a "normal" hair can be useful in diagnosis. For example, lead poisoning results in high levels of lead in the hair. However, the use of hair analysis as a screening test to determine the health or nutritional status of an individual remains unreliable.
Staphylococcus aureus is commonly found in pimples, boils, and carbuncles and causes impetigo (im-pe-ti'go), a disease of the skin that usually affects children and that is characterized by small blisters containing pus that easily rupture and form a thick, yellowish crust. Streptococcus pyogenes causes erysipelas (er-i-sip' e-las), swollen red patches in the skin. Burns are often infected by Pseudomonas aeruginosa, producing a characteristic blue-green pus caused by bacterial pigment.
Acne is a disorder of the hair follicles and sebaceous glands that affects almost everyone at some time or another. Although the exact cause of acne is unknown, four factors are believed to be involved: hormones, sebum, abnormal keratinization within the hair follicle, and the bacterium Propioni-bacterium acnes. The lesions apparently begin with a hyperproliferation of the hair follicle epidermis, and many cells are desquamated. These cells are abnormally sticky and adhere to each other to form a mass of cells mixed with sebum that blocks the hair follicle. During puberty, hormones, especially testosterone, stimulate the sebaceous glands to increase sebum production. Because both the adrenal gland and the testes produce testosterone, the effect is seen in males and females. An accumulation of sebum behind the blockage produces a whitehead, which may continue to develop into a blackhead and/or a pimple. A blackhead results if the opening of the hair follicle is pushed open by the accumulating confined cells and sebum. Although there is general agreement that dirt is not responsible for the black color of blackheads, the exact cause of the black color is disputed. A pimple develops if the wall of the hair follicle ruptures. Once the wall of the follicle ruptures, P. acnes and other microorganisms stimulate an inflammatory response that results in the formation of a red pimple filled with pus. If tissue damage is extensive, scarring occurs.
Some of the well-known viral infections of the skin include chickenpox, measles, German measles, and cold sores (herpes simplex). Warts, which are caused by a viral infection of the epidermis, are generally harmless and usually disappear with treatment.
Ringworm is a fungal infection that affects the keratinized portion of the skin, hair, and nails and produces patchy scaling and an inflammatory response. The lesions are often circular with a raised edge and in ancient times were thought to be caused by worms. Several species of fungus cause ringworm in humans and are usually described by their location on the body; in the scalp the condition is ringworm, in the groin it is jock itch, and in the feet it is athlete's foot.
Decubitus (de-ku'bi-tus) ulcers, also known as bedsores or pressure sores, develop in patients who are immobile (for example, bedridden or confined to a wheelchair). The weight of the body, especially in areas over bony projections such as the hip bones and heels, compresses tissues and causes ischemia (is-ke'me-ah) or reduced circulation. The consequence is destruction, or necrosis (ne-kro'sis), of the hypodermis and deeper tissues that is followed by death of the skin. Once the skin dies, microorganisms gain entry to produce an infected ulcer.
Bullae (bul'e) are fluid-filled areas in the skin that develop when tissues are damaged, and the resultant inflammatory response produces edema. Infections or physical injuries can cause bullae or lesions in different layers of the skin.
The cause of psoriasis (so-ri'-a-sis) is unknown, although there may be a genetic component. An increase in mitotic activity in the stratum basle, abnormal keratinization, and elongation of the dermal papillae toward the skin surface result in a thicker-than-normal stratum corneum that desquamates to produce large, silvery scales. If the scales are scraped away, bleeding occurs from the blood vessels at the top of the dermal papillae. Psoriasis is a chronic disease that can be controlled but as yet has no cure.
Eczema and Dermatitis
Eczema (ek'ze-mah) and dermatitis (der'ma-ti'tis) are inflammatory conditions of the skin. Cause of the inflammation can be allergy, infection, poor circulation, or exposure to physical factors such as chemicals, heat and cold, or sunlight.
Birthmarks are congenital (present at birth) disorders of the capillaries in the dermis of the skin. Usually they are only of concern for cosmetic reasons. A strawberry birthmark is a mass of soft, elevated tissue that appears bright red to deep purple in color. In 70% of patients, strawberry birthmarks disappear spontaneously by the age of seven. Port-wine stains appear as flat, dull red or bluish patches that persist throughout life.
Vitiligo (vit-i-li'-go) is the the development of patches of the white skin because the melanocytes in the affected area are destroyed, apparently by an autoimmune response.
A mole is an elevation of the skin that is variable in size and is often pigmented and hairy. Histologically, a mole is an aggregation or "nest" of melanocytes in the epidermis or dermis. They are a normal occurrence, and most people have 10 to 20 moles, which appear in childhood and enlarge until puberty.
Skin cancer is the most common type of cancer. Although chemicals and radiation (x-rays) are known to induce cancer, the development of skin cancer is most often associated with exposure to ultraviolet radiation from the sun, and consequently, most skin cancers develop on the face or neck. The group of people most likely to have skin cancer are those who are fair skinned (that is, have less protection from the sun) or those over the age of 50 (have had long exposure to the sun).
Basal cell carcinoma, the most frequent skin cancer, begins in the stratum basale and extends into the dermis to produce an open ulcer. Surgical removal or radiation therapy cures this type of cancer, and fortunately there is little danger that the cancer will spread, or metastasize (me-tas'ta-siz), to other areas of the body if treated in time.
Squamous cell carcinoma develops from stratum spinosum keratinocytes that continue to divide as they produce keratin. Typically the result is a nodular, keratinized tumor confined to the epidermis, but it can invade the dermis, metastasize, and cause death.
Malignant melanoma is a less common form of skin cancer that arises from melanocytes, usually in a preexisting mole. The melanoma can appear as a large, flat, spreading lesion or as a deeply pigmented nodule. Metastasis is common, and unless diagnosed and treated early in development, this cancer is often fatal. Other types of skin cancer are possible (for example, metastasis from other parts of the body to the skin).
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