CLINICAL BOX
INTEGUMENTARY SYSTEM
Skin Color Signs in Physical Diagnosis
v Blood flow through the superficial capillary beds of the dermis affects the color of skin and can provide important clues for diagnosing certain clinical conditions. When the blood is not carrying enough oxygen from the lungs, such as in a person who has stopped breathing or whose circulation is unable to send adequate amount of blood through the lungs, the skin can appear bluish (cyanotic). Cyanosis occurs because the oxygen-carrying hemoglobin of blood appears bright red when carrying oxygen (as it does in arteries and usually does in capillaries) and appears deep, purplish blue when depleted of oxygen, as it does in veins. Cyanosis is especially evident where skin is thin, such as the lips, eyelids, and deep to the transparent nails. Skin injury, exposure to excess heat, infection, inflammation, or allergic reactions may cause the superficial capillary beds to become engorged, making the skin look abnormally red, a sign called erythema. In certain liver disorders, a yellow pigment called bilirubin builds up in the blood, giving a yellow appearance to the whites of the eyes and skin, a condition called jaundice. Skin color changes are most readily observed in people with light-colored skin and may be difficult to discern in people with dark skin.
Skin Incisions and Scarring
v The skin is always under tension. In general, lacerations or incisions that parallel the tension lines usually heal well with little scarring because there is minimal disruption of collagen fibers. The uninterrupted fibers tend to retain the cut edges in place. However, a laceration or incision across the tension lines disrupts more collagen fibers. The disrupted lines of force cause the wound to gape, and it may heal with excessive (keloid) scarring. When other considerations, such as adequate exposure and access or avoidance of nerves, are not of greater importance, surgeons attempting to minimize scarring for cosmetic reasons may use surgical incisions that parallel the tension lines.
Stretch Marks in Skin
v The collagen and elastic fibers in the dermis form a tough, flexible meshwork of tissue. Because the skin can distend considerably, a relatively small incision can be made during surgery compared with the much larger incision required to attempt the same procedure in an embalmed cadaver, which no longer exhibits elasticity. The skin can stretch and grow to accommodate gradual increases in size. However, marked and relatively fast size increases, such as the abdominal enlargement and weight gain accompanying pregnancy, can stretch the skin too much, damaging the collagen fibers in the dermis. During pregnancy, stretch marks (L. striae gravidarum)—bands of thin wrinkled skin, initially red but later becoming purple or white—may appear on the abdomen, buttocks, thighs, and breasts. Stretch marks also form outside of pregnancy (L. striae cutis distensae) in obese individuals and in certain diseases (e.g., hypercortisolism or Cushing syndrome); they occur along with distension and loosening of the deep fascia due to protein breakdown leading to reduced cohesion between the collagen fibers. Stretch marks generally fade after pregnancy and weight loss, but they never disappear completely.
Skin Injuries and Wounds
v Lacerations. Accidental cuts and skin tears are superficial or deep. Superficial lacerations penetrate the epidermis and perhaps the superficial layer of the dermis; they bleed but do not interrupt the continuity of the dermis. Deep lacerations penetrate the deep layer of the dermis, extending into the subcutaneous tissue or beyond; they gape and require approximation of the cut edges of the dermis (by suturing, or stitches) to minimize scarring.
v Burns. Burns are caused by thermal trauma, ultraviolet or ionizing radiation, or chemical agents. Burns are classified, in increasing order of severity, based on the depth of skin injury and the need for surgical intervention. The current classification system does not use numerical designations except for fourth-degree burns (the most severe):
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Superficial burn (e.g., sunburn): damage is limited to the epidermis; symptoms are erythema (hot red skin), pain, and edema (swelling); desquamation (peeling) of the superficial layer usually occurs several days later, but the layer is quickly replaced from the basal layer of the epidermis without significant scarring.
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Partial-thickness burn: epidermis and superficial dermis are damaged with blistering (superficial partial thickness) or loss (deep partial thickness); nerve endings are damaged, making this variety the most painful; except for their most superficial parts, the sweat glands and hair follicles are not damaged and can provide the source of replacement cells for the basal layer of the epidermis along with cells from the edges of the wound; healing occurs slowly (3 weeks to several months), leaving scarring and some contracture, but it is usually complete.
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Full-thickness burn: the entire thickness of the skin is damaged and often the subcutaneous tissue; there is marked edema and the burned area is numb since sensory endings are destroyed; minor degree of healing may occur at the edges, but the open, ulcerated portions require skin grafting: dead material (eschar) is removed and replaced (grafted) over the burned area with skin harvested (taken) from a nonburned location (autograft) or using skin from human cadavers or pigs or cultured or artificial skin.
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4th-degree burn: damage extends through the entire thickness of the skin into underlying fascia, muscle, or bone; these injuries are life threatening.
v Burns are classified as severe if they cover 20% or more of the total body surface area (excluding superficial burns like sunburn), are complicated by trauma or inhalation injury, or are caused by chemicals or high-voltage electricity. One way to estimate the surface area affected by a burn in an adult is to apply the “rule of nines,” in which the body is divided into areas that are approximately 9% or multiples of 9% of the total body surface. Three factors that increase the risk of death from burn injury are (1) age older than 60 years, (2) partial-thickness and full-thickness burns of over 40% body surface area, and (3) the presence of inhalation injury.