OVERVIEW AND BASIC CONCEPTS PART-8
INTEGUMENTARY SYSTEM 2
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Hair follicles are generally slanted to one side, and several sebaceous glands lie on the side the hair is directed toward (“points to”) as it emerges from the skin.
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Thus, contraction of the arrector muscles causes the hairs to stand up straighter, thereby compressing the sebaceous glands and helping them secrete their oily product onto the skin surface.
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The evaporation of the watery secretion (sweat) of the sweat glands from the skin provides a thermoregulatory mechanism for heat loss (cooling).
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Also involved in the loss or retention of body heat are the small arteries (arterioles) within the dermis.
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They dilate to fill superficial capillary beds to radiate heat (skin appears red) or constrict to minimize surface heat loss (skin, especially of the lips and fingertips, appears blue).
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Other skin structures or derivatives include the nails (fingernails, toenails), the mammary glands, and the enamel of teeth.
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Located between the overlying skin (dermis) and underlying deep fascia, the subcutaneous tissue (superficial fascia) is composed mostly of loose connective tissue and stored fat and contains sweat glands, superficial blood vessels, lymphatic vessels, and cutaneous nerves.
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The neurovascular structures of the integument (cutaneous nerves, superficial vessels) course in the subcutaneous tissue, distributing only their terminal branches to the skin.
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The subcutaneous tissue provides for most of the body’s fat storage, so its thickness varies greatly, depending on the person’s nutritional state. In addition, the distribution of subcutaneous tissue varies considerably in different sites in the same individual.
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Compare, for example, the relative abundance of subcutaneous tissue evident by the thickness of the fold of skin that can be pinched at the waist or thighs with the anteromedial part of the leg (the shin, the anterior border of the tibia) or the back of the hand, the latter two being nearly devoid of subcutaneous tissue.
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Also consider the distribution of subcutaneous tissue and fat between the sexes: In mature females, it tends to accumulate in the breasts and thighs, whereas in males, subcutaneous fat accumulates especially in the lower abdominal wall.
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Subcutaneous tissue participates in thermoregulation, functioning as insulation, retaining heat in the body’s core. It also provides padding that protects the skin from compression by bony prominences, such as those in the buttocks.
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Skin ligaments (L. retinacula cutis), numerous small fibrous bands, extend through the subcutaneous tissue and attach the deep surface of the dermis to the underlying deep fascia. The length and density of these ligaments determines the mobility of the skin over deep structures.
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Where skin ligaments are longer and sparse, the skin is more mobile, such as on the back of the hand.Where ligaments are short and abundant; the skin is firmly attached to the underlying deep fascia, such as in the palms and soles.
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In dissection, removal of skin where the skin ligaments are short and abundant requires use of a sharp scalpel. The skin ligaments are long but particularly well developed in the breasts, where they form weight-bearing suspensory ligaments.