Introduction: Skin Disorders
Introduction: Skin Disorders: Excerpt from Professional Guide to Diseases (Eighth Edition)
Skin is man’s front-line protective barrier between internal structures and the external environment. It’s tough, resilient, and virtually impermeable to aqueous solutions, bacteria, or toxic compounds. It also performs many vital functions. Skin protects against trauma, regulates body temperature, serves as an organ of excretion and sensation, and synthesizes vitamin D in the presence of ultraviolet light. Skin varies in thickness and other qualities from one part of the body to another, which often accounts for the distribution of skin diseases.
Skin has three primary layers: epidermis, dermis, and subcutaneous tissue. The epidermis (the outermost layer) produces keratin as its primary function. This layer is generally thin but is thicker in areas subject to constant pressure or friction, such as the soles and palms. The epidermis contains two sublayers: the stratum corneum, an outer horny layer of keratin that protects the body against harmful environmental substances and restricts water loss, and the cellular stratum, where keratin cells are synthesized. The basement membrane lies beneath the cellular stratum and serves to attach the epidermis to the dermis.
The cellular stratum, the deepest layer of the epidermis, consists of the basal layer, where mitosis takes place; the stratum spinosum, where cells begin to flatten, and fibrils — precursors of keratin — start to appear; and the stratum granulosum, made up of cells containing deeply staining granules of keratohyalin, which are generally thought to become the keratin that forms the stratum corneum. A skin cell moves from the basal layer of the cellular stratum to the stratum corneum in about 14 days. After another 14 days, normal wear and tear on the skin causes it to slough off. The epidermis also contains melanocytes, which produce the melanin that gives the skin its color, and Langerhans cells, which are involved in a variety of immunologic reactions.
The dermis, the second primary layer of the skin, consists of two fibrous proteins, fibroblasts, and an intervening ground substance. The proteins are collagen, which strengthens the skin to prevent it from tearing, and elastin to give it resilience. The ground substance, which makes the skin soft and compressible, contains primarily jellylike mucopolysaccharides. Two distinct layers constitute the dermis: the papillary dermis (top layer) and the reticular dermis (bottom layer).
Subcutaneous tissue, the third primary layer of the skin, consists mainly of fat (containing mostly triglycerides), which provides heat, insulation, shock absorption, and a reserve of calories. Both sensory and motor nerves (autonomic fibers) are found in the dermis and the subcutaneous tissue.
Nails, glands, and hair
Nails are epidermal cells converted to hard keratin. The bed on which the nail rests is highly vascular, making the nail appear pink; the whitish, crescent-shaped area extending beyond the proximal nail fold, called the lunula — most visible in the thumbnail — marks the end of the matrix, the site of mitosis and of nail growth.
Sebaceous glands, found everywhere on the body (but mostly on the face and scalp) except the palms and soles, serve as appendages of the dermis. These glands generally excrete sebum into hair follicles, but in some cases, they empty directly onto the skin surface. Sebum is an oily substance that helps keep the skin and hair from drying out and prevents water and heat loss. Sebaceous glands abound on the scalp, forehead, cheeks, chin, back, and genitalia, and may be stimulated by sex hormones — primarily testosterone.
The dermis and subcutaneous tissue contain eccrine and apocrine glands, and hair. Eccrine sweat glands open directly onto the skin and regulate body temperature. Innervated by sympathetic nerves, these sweat glands are distributed throughout the body, except for the lips, ears, and parts of the genitalia. They secrete a hypertonic solution made up mostly of water and sodium chloride; the prime stimulus for eccrine gland secretion is heat. Other stimuli include muscular exertion and emotional stress.
Apocrine sweat glands appear chiefly in the axillae and genitalia; they’re responsible for producing body odor and are stimulated by emotional stress. The sweat produced is sterile but undergoes bacterial decomposition on the skin surface. These glands become functional after puberty. (Ceruminous glands, located in the external ear canal, appear to be modified sweat glands and secrete a waxy substance known as cerumen.)
Hair grows on most of the body, except for the palms, the soles, and parts of the genitalia. An individual hair consists of a shaft (a column of keratinized cells), a root (embedded in the dermis), the hair follicle (the root and its covering), and the hair papilla (a loop of capillaries at the base of the follicle). Mitosis at the base of the follicle causes the hair to grow; the papilla provides nourishment for mitosis. Small bundles of involuntary muscles known as arrectores pilorum cling to hair follicles. When these muscles contract, usually during moments of fear or shock, the hairs stand on end, and the person is said to have goose bumps or gooseflesh. Melanocytes in the matrix (inner core) of the hair bulb produce melanin, which passes into the innermost layers of the hair and is responsible for hair color. Dark hair contains mostly true melanin. Blond and red hair contains variants of melanin that have iron and more sulfur. Gray hair results from pigment loss due to a decline of tyrosinase, which is required for melanin synthesis. White hair occurs when air bubbles accumulate in the center of the hair shaft.
Vascular influence
The skin is served by a vast arteriovenous network, extending from subcutaneous tissue to the dermis. These blood vessels provide oxygen and nutrients to sensory nerves (which control touch, temperature, and pain), motor nerves (which control the activities of sweat glands, the arterioles, and smooth muscles of the skin), and skin appendages. Blood flow also influences skin coloring because the amount of oxygen carried to capillaries in the dermis can produce transient changes in color. For example, decreased oxygen supply can turn the skin pale or bluish; increased oxygen can turn it pink or ruddy.
Assessing skin disorders
Assessment begins with a thorough patient history to determine whether a skin disorder is an acute flare-up, a recurrent problem, or a chronic condition. Ask the patient how long he has had the disorder; how a typical flare-up or attack begins; whether or not it itches; and what medications — systemic or topical — have been used to treat it. Also, find out if any of his family members, friends, or contacts have the same disorder, and if he lives or works in an environment that could cause the condition. Also ask about hobbies.
When examining a patient with a skin disorder, be sure to look everywhere — mucous membranes, hair, scalp, axillae, groin, palms, soles, and nails. Note moisture, temperature, texture, thickness, mobility, edema, turgor, and any irregularities in skin color. Look for skin lesions; if you find a lesion, record its color, size, and location. (See Primary skin lesions, page 1230. Also see Secondary changes in primary skin lesions, page 1231.) Try to determine which is the primary lesion — the one that appeared first — which always starts in normal skin. The patient might be able to point it out.
If more than one lesion is in evidence, note the pattern of distribution. Lesions can be localized (isolated), regional, general, or universal (total), involving the entire skin, hair, and nails. Also, observe whether the lesions are unilateral or bilateral and symmetrical or asymmetrical; also note the arrangement of the lesions (clustered or linear configuration, for example).
Diagnostic aids
After simple observation, and examination of the affected area of the skin with a dermatoscope for morphologic detail, the following clinical diagnostic techniques may help to identify skin disorders:
❑ Biopsy determines histology of cells, and may be diagnostic, confirmatory, or inconclusive, depending on the disease.
❑ Diascopy, in which a lesion is covered with a microscopic slide or piece of clear plastic, helps determine whether dilated capillaries or extravasated blood is causing the redness of a lesion.
❑ Gram’s stains and exudate cultures help identify the organism responsible for an underlying infection.
❑ Microscopic immunofluorescence identifies immunoglobulins and elastic tissue in detecting skin manifestations of immunologically mediated disease.
❑ Patch tests identify contact sensitivity (usually with dermatitis).
❑ Potassium hydroxide preparations permit examination for mycelia in fungal infections.
❑ Side-lighting shows minor elevations or depressions in lesions; it also helps determine the configuration and degree of eruption.
❑ Subdued lighting highlights the difference between normal skin and circumscribed lesions that are hypopigmented or hyperpigmented.
❑ Wood’s light examination reveals yellow, green, or blue-green fluorescence when an area is infected with certain dermatophytes (fungi).
Special considerations
When assessing a skin disorder, keep in mind its distressing social and psychological implications. Unlike internal disorders, such as cardiac disease or diabetes mellitus, a skin condition is usually obvious and disfiguring. Understandably, the psychological implications are most acute when skin disorders affect the face — especially during adolescence, an emotionally turbulent time of life. However, such disorders can also create tremendous psychological problems for adults. A skin disease usually interferes with a person’s ability to work because the condition affects the hands or because it distresses the patient to such an extent that he can’t function.
For these reasons, be empathetic and accepting. Above all, don’t be afraid to touch such a patient; most skin disorders aren’t contagious. Touching the patient naturally and without hesitation helps show your acceptance of the dermatologic condition. Such acceptance is no less important than your patient teaching about the disease and your guidance and help with carrying out prescribed treatment.
Pictures
Book Source Details
- Book Title: Professional Guide to Diseases (Eighth Edition)
- Author(s): Springhouse
- Year of Publication: 2005
- Copyright Details: Professional Guide to Diseases (Eighth Edition), Copyright © 2005 Lippincott Williams & Wilkins.
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Copyright notice for book excerpts: Copyright © 2008 Lippincott Williams & Wilkins. All rights reserved.
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