Chapter II - Dermatology
APPENDAGES OF THE SKIN
Appendages of the skin:
Appendages of the skin are nails, hair, sebaceous glands and sweat glands.
Hairs and nails are modified epidermal cells composed of keratin. Hairs grow from a cavity called hair follicle, which is located in the dermis as seen in the figure. Hair follicle is lined with epidermal cells.
At the base of the hair follicle is an enlarged hair bulb. At the bottom of it is the papilla, which contains connective tissues and blood vessels to provide nourishment to the hair. It is from these cells in this region that the hair grows. The hair projects above the body surface as hair shaft. The portion that penetrates in the dermis (in the hair follicle) is called the root. Associated with the hair follicles are minute specialized smooth involuntary muscles called arrector pilus, which contract during stress and raise the hair and pull it in an upright position. Also sebaceous glands are connected to the hair follicles, which secrete a fatty or oily substance called sebum. It keeps the skin soft, smooth and gives a glossy feeling to the hair. Hairs grow in two phases; anagen or growing phase and telogen or resting phase.
Nails are also composed of keratin. They are present on the distal ends of fingers and toes. The nail lies on the nailbed in which dermis is arranged in longitudinal ridges. The nailbed is supplied with nerve endings and blood vessels. Nail grows from root of the nail, which lies in the groove of the skin called the nail grooves. Nail is thinnest in this region. The body of a nail is the uncovered part, which is firmly attached to the nailbed. Its distal end is free and called free border.
Sweat secretes from the sweat glands. It is essentially a saline solution comprising about one-third of the concentration of plasma. Its secretion is under the control of the sympathetic nervous system. Body temperature can be lowered by means of sweat glands. Sweating varies from 0 to 2000 ml per day, depending upon requirements of body temperature regulation.
During physical assessment of a patient, it is imperative for the examining physician to take note of the skin condition. The physician has to look for skin texture, moistness or dryness, tenderness, skin turgor, and most importantly temperature. The physician also evaluates the skin color for any abnormality like cyanosis, erythema, jaundice, etc., and sees the pigmentation pattern of the skin. The examiner also inspects the skin for any hemorrhagic lesions like petechiae, purpura, and ecchymosis, or structural changes on the skin like macule, vesicles, bullae, wheals, pustules, papules, plaque, nodules, scales, excoriations, fissures, scars, ulcers, or lichenifications. A variety of skin conditions and diseases can be properly diagnosed by a proper assessment of skin condition. Not only that, even systemic condition can be reflected many times to the skin surface, like jaundice and cystic fibrosis, in which skin is the primary indicator of the underlying disease.
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Chapter II - Dermatology