OVERVIEW AND BASIC CONCEPTS PART-8
INTEGUMENTARY SYSTEM 1
Ø Because the skin (L. integumentum, a covering) is readily accessible and is one of the best indicators of general health, careful observation of it is important in physical examinations. It is considered in the differential diagnosis of almost every disease. The skin provides:
· Protection of the body from environmental effects, such as abrasions, fluid loss, harmful substances, ultraviolet radiation, and invading microorganisms.
· Containment for the body’s structures (e.g., tissues and organs) and vital substances (especially extracellular fluids), preventing dehydration, which may be severe when extensive skin injuries (e.g., burns) are experienced.
· Thermal regulation through the evaporation of sweat and/or the dilation or constriction of superficial blood vessels.
· Sensation (e.g., pain) by way of superficial nerves and their sensory endings.
· Synthesis and storage of vitamin D.
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The skin, the body’s largest organ, consists of the epidermis, a superficial cellular layer, and the dermis, a deep connective tissue layer.
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The epidermis is a keratinized epithelium—that is, it has a tough, horny superficial layer that provides a protective outer surface overlying its regenerative and pigmented deep or basal layer.
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The epidermis has no blood vessels or lymphatics. The avascular epidermis is nourished by the underlying vascularized dermis.
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The dermis is supplied by arteries that enter its deep surface to form a cutaneous plexus of anastomosing arteries.
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The skin is also supplied with afferent nerve endings that are sensitive to touch, irritation (pain), and temperature. Most nerve terminals are in the dermis, but a few penetrate the epidermis.
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The dermis is a dense layer of interlacing collagen and elastic fibers. These fibers provide skin tone and account for the strength and toughness of skin.
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The dermis of animals is removed and tanned to produce leather. Although the bundles of collagen fibers in the dermis run in all directions to produce a tough felt-like tissue, in any specific location most fibers run in the same direction.
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The predominant pattern of collagen fibers determines the characteristic tension and wrinkle lines in the skin.
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The tension lines (also called cleavage lines or Langer lines) tend to spiral longitudinally in the limbs and run transversely in the neck and trunk.
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Tension lines at the elbows, knees, ankles, and wrists are parallel to the transverse creases that appear when the limbs are flexed.
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The elastic fibers of the dermis deteriorate with age and are not replaced; consequently, in older people, the skin wrinkles and sags as it loses its elasticity.The skin also contains many specialized structures.
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The deep layer of the dermis contains hair follicles, with associated smooth arrector muscles and sebaceous glands. Contraction of the arrector muscles of hairs (L. musculi arrector pili) erects the hairs, causing goose bumps.
