Structure and Function

The integumentary system is composed of the skin and accessory structures (Fig. 10-1). Accessory structures of the system include the hair, nails, specialized glands, and nerves. The main function of the integumentary system is to protect the other body systems from injury and infection. A second function is to help the body maintain homeostasis by regulating temperature, retaining body fluids, and eliminating wastes. The skin also helps to perceive the environment with sensory receptors. The skin stores energy and vitamins and produces vitamin D from sunlight. Some hormones, fat-soluble vitamins, and drugs may be absorbed through the skin.

Skin

The skin, covering 17 to 20 square feet (1.6 to 1.9 m²), is the largest organ in the body. It varies in thickness from inch (0.5 mm) in the eyelids to inch (6.3 mm) in the soles of the feet. Changes in the skin often indicate the presence of other body system disorders, including anemia, respiratory disorders, liver disorders, cancer, and shock (Fig. 10-2).

Brain Byte

The skin plays a major role in maintaining homeostasis by regulating body temperature.

The epidermis, or cuticle, is the outermost layer of the skin and is composed of a surface of dead cells with an underlying layer of living cells. Water-repellent cells made of protein (keratinocytes) make up 90% of the epidermis. Oil (sebaceous) and sweat (sudoriferous) glands and hair follicles lie in the epidermis. Melanocytes, which produce melanin, are located in this layer. Melanin is the pigment that gives skin its color (Fig. 10-3). The surface of the epidermis is covered with a film composed of sweat, oil, and epithelial cells that lubricates, hydrates, provides antibacterial protection, and blocks toxic agents from entering the body.

The dermis, or corium, is called the “true” skin. The dermis contains the blood vessels and nerves. Each inch of skin contains 15 square feet of blood vessels. The innermost layer of the skin is called the subcutaneous layer. Fatty (adipose) tissue of the subcutaneous layer cushions and insulates the body’s organs. The nerve endings in the skin allow it to be sensitive to environmental stimuli. Skin senses pain, pressure, touch, and changes in temperature.

Hair and Hair Follicles

Skin normally has hair (pilus) in all areas except the soles of the feet and palms of the hands. Some hair blocks foreign particles from entering the body through structures such as the nose and eyes.

Each hair root originates in the dermis. The visible portion is called the shaft. The hair follicle is the root with its covering. One or two oil (sebaceous) glands are attached to each hair follicle. A tiny muscle (arrector pili) is attached to the hair shaft and causes “goose bumps” or the hair to “stand on end” in response to cold or fear (Fig. 10-4). Hair color and texture are inherited. The color depends on the amount of melanin in the cells.

Nails

The function of the nails is to protect fingers and toes from injury. Fingernails and toenails are formed from dead, keratinized epidermal cells. The root or area of nail growth is covered by skin at the area of attachment to finger or toe. The crescent-shaped white area near the root is the lunula (Fig. 10-5).

Brain Byte

After compression, a return of normal color to the tissue under the nail bed within 2 seconds indicates good circulation.

Assessment Techniques

Dermatology is the study of skin. Dermatitis is the general term for inflammation of the skin. Skin disorders are usually uncomfortable and unattractive but not life threatening.

Assessment of the skin, hair, and nails includes palpation, olfactory (smell), and visual inspection. The color, temperature, texture, turgor (fullness or tension), and any moisture should be noted. The color of skin is genetically determined. Any change—such as paleness (pallor), redness (erythema), yellowishness (jaundice), or blueness (cyanosis)—may indicate a problem. Normal skin is warm, dry, and without open sores (intact). When a pinch or fold of skin on the forearm is lifted, it should rise easily and return to place quickly when released.

Skin lesions can usually be seen with visual inspection. The size, shape, texture, and color of a lesion often help reveal its cause. A biopsy or culture may be used to identify the causative organism.

The uppermost part of the dermis is composed of papillae, or ridges. The papillae form regular patterns in the fingers, palms of the hands, and soles of the feet, where the skin is thick. Fingertip and toe prints are unique to each person. In addition to forming a surface that permits gripping, the fingerprints allow the identification of each individual. The patterns of ridges in fingerprints and toe prints may also be linked to disorders such as Down syndrome.

Disorders of the Integumentary System

Acne vulgaris (AK-nee vul-GAYR-is) usually appears in adolescence and may continue into adulthood. Acne is often caused by the increased secretion of oil (sebum) related to increased hormones during puberty. Bacterial growth and blockage of the hair follicles cause papules, pustules, and blackheads. Acne primarily affects the face, chest, and back. Acne tends to run in families. Contrary to popular belief, diet does not cause or affect the severity of acne. Treatment may include exposure to ultraviolet light, oral or topical antibiotics, or removal of the top layers of skin that has scarred (dermabrasion).

Albinism (AL-bin-izm) is a rare inherited disorder in which the melanocytes do not produce enough or any melanin. Lack of melanin leads to pale skin, white hair, and pink eyes. People with albinism are prone to severe sunburn, and light may damage unprotected structures of the eyes. Although no cure for albinism exists, wearing sunglasses, applying sunscreen, and avoiding exposure to the sun may help avoid skin cancer and eye damage.

Alopecia (al-o-PEE-shee-uh), or baldness, is the inherited tendency to lose hair from the head. Production of androgenic (an-dro-JEN-ik) hormones beginning at puberty initiates the loss. Baldness is more common in men, but it may occur in women and may begin at any age. Drugs, radiation, pregnancy, high fever, anorexia, and cosmetics may cause temporary hair loss.

Athlete’s foot, or epidermophytosis (ep-i-DER-mo-fi-TOE-sis) is a common fungal infection. The skin may itch, blister, and crack, especially between the toes. Athlete’s foot most often occurs during warm weather and is contagious. It can be transmitted on wet floors, such as in gym showers. Treatment includes application of antifungal medication and keeping the area clean, ventilated, and dry. More serious infections may be treated with an oral antifungal medication.

Cellulitis (sel-yoo-LIE-tis) is a bacterial infection of the dermis and subcutaneous layer of the skin. Cellulitis may be caused by many different bacteria but is commonly caused by Streptococcus organisms. It occurs in people with low resistance to infection, such as older patients, children, and chronically ill patients. The infected person may experience fever, chills, and vesicles (VES-i-kulz) on a reddened, warm area of the skin. It most commonly occurs on legs and may cause impaired circulation and permanent lymphedema (lim-feh-DEE-muh). Treatment includes rest, immobilization and elevation of the infected area, and antibiotics.

Chloasma (klo-AZ-muh), or melasma, is a patchy discoloration of the face caused by high hormone levels that occur during pregnancy and by prolonged use of oral contraceptives. It may disappear at the end of the pregnancy or with stopping birth control pills. Chloasma may also be a sign of liver problems. Treatment is often unnecessary, but nonprescription cosmetic products can minimize the discoloration.

Cleft lip or cleft palate (kleft PAL-ut) occurs in 1 of 1000 (cleft lip) and 1 in 2000 (cleft palate) infants. In this condition the upper lip has a cleft or space where the nasal processes or palate does not meet properly. Heredity appears to be the direct cause in 25% of the cases, and environmental factors and premature birth may also cause the condition. Treatment includes surgical and dental correction, speech therapy, and psychological counseling.

Contact dermatitis is an allergic reaction that may occur after initial contact or as an acquired response. Some substances that commonly cause acquired dermatitis include poison ivy, nickel in jewelry, and preservatives in cosmetics. Latex in gloves may be an allergen for some health care workers. Redness, itching, swelling, and blisters may result from contact with the irritating substance. Treatment may include washing the affected area, applying anti-inflammatory creams, and avoiding exposure to the irritating substance.

Dandruff (DAN-druf), characterized by itching of the scalp, produces white flakes of dead skin cells. Massaging the scalp and brushing and shampooing the hair can control dandruff. Medicated shampoos designed to control dandruff often help.

Decubitus ulcers (de-KYOO-bit-us UL-serz), or decubiti, are sores or areas of inflammation that occur over bony prominences of the body as a result of prolonged pressure and hypoxia to the affected tissues. These “bedsores” are seen most often in older patients and in patients who cannot move themselves (immobilized). Frequent changes in position, good nutrition, and massage to the area help to prevent decubiti. Prevention of decubiti is easier than treatment. Decubiti are described in four stages by their severity and can be life threatening. Decubiti are often resistant to treatment, which may include application of antibiotics, removal of necrotic tissue, and frequent cleaning of open sores. Larvae (maggots) of blowflies, which feed only on dead tissue, have been used in some severe cases to clean sores. In addition to removing the dead tissue, the maggot larvae provide stimulation of the affected area with their movement and produce compounds that are lethal to bacteria that cause gangrene and similar infections. Deep pressure sores may require skin grafting. Negative pressure wound therapy (vacuum-assisted closure), as well as hyperbaric chamber therapy, may be used in some cases.

Eczema (EK-ze-muh), a form of dermatitis, is a group of disorders caused by allergic or irritant reactions. Eczema is characterized by swelling; redness; and itching, weeping, crusted skin lesions. Although it is not contagious, it seems to run in families. Eczema is chronic but may disappear as affected children become older. Treatment of eczema includes removing the irritant and keeping the affected skin clean and well moisturized. It is also helpful to avoid sudden changes in temperature and overheating. Outbreaks may disappear by avoiding harsh soaps and environmental factors or food that trigger outbreaks, as well as reducing stress.

Fungal (FUN-gul) skin infections live only on the dead, outer surface or epidermis. Some may cause no symptoms. Others may produce irritation, scaling, redness, swelling, or blisters. Most fungal infections occur in areas of the body that provide moisture and are named by the area in which they appear. Examples include athlete’s foot (see earlier); jock itch; and scalp, nail, body, and beard ringworm. Fungal infections of the scalp or beard can cause hair loss. Treatment by the use of antifungal creams usually cures these skin conditions. In severe cases, oral antifungal medication may be necessary. Fungal infections of the skin may be prevented by keeping the skin dry; wearing loose, clean clothing; and avoiding shared use of towels, combs, and hairbrushes.

Furuncle (FER-ung-kl), commonly called a boil, is a bacterial infection of a hair follicle. Although it is usually caused by Staphylococcus aureus (S. aureus), it may result from other bacteria or fungi. A carbuncle is several boils that join together. Recurring boils may indicate diabetes or an immune disorder. Boils are infectious, but the spread can be controlled with careful cleanliness and handwashing. Treatment includes hot compresses, antibiotics, and sometimes drainage by lancing. Boils may also be caused by methicillin-resistant S. aureus (MRSA). More information about MSRA is found in Chapter 3.

Hirsutism (HER-soot-izm), or hypertrichosis (hy-per-tri-KO-sis), is an abnormal amount of hair growth in unusual places. In women hair may appear on the face, back, and chest. Hirsutism may be caused by hormone supplements or may be a hereditary condition. Unwanted hair may be removed temporarily by shaving, waxing, or using depilatories, or it may be removed permanently by electrolysis. The disorder causing the hair growth, if any, should be treated when possible.

Impetigo (im-puh-TI-go) is a contagious bacterial skin infection that occurs most often in children. Impetigo is most often caused by S. aureus. It begins with small vesicles, which become pustules and form a crust. Itching and burning may occur. Ecthyma is a form of impetigo that creates open sores (ulcers) on the skin. Impetigo may lead to kidney infection, but lesions usually clear without causing lasting damage. It can be fatal in infants. Treatment includes antibiotics and isolation to prevent spread of the infection.

Kaposi sarcoma (KS) (kuh-POH-see sahr-KOH-muh) (Fig. 10-6) is a form of cancer that originates in blood vessels and spreads to the skin. KS appears as a round or oval spot on the skin that may be red, purplish, or brown in color. It has two forms. One form affects older people and rarely spreads to other parts of the body. The second form is associated with diabetes, lymphoma, and AIDS. It grows more quickly and may spread to the lungs, liver, and intestines. Treatment for KS may include local treatment, systemic chemotherapy, or interferon.

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