Sweat Glands

Sweat glands, or sudoriferous28 (soo-dor-IF-er-us) glands, are of two kinds, described in chapter 5: merocrine and apocrine. Merocrine (eccrine) sweat glands, the most numerous glands of the skin, produce watery perspiration that serves primarily to cool the body (fig. 6.11a). There are 3 to 4 million merocrine sweat glands in the adult skin,

Saladin: Anatomy & I 6. The Integumentary I Text I I © The McGraw-Hill

Physiology: The Unity of System Companies, 2003 Form and Function, Third Edition

206 Part Two Support and Movement with a total weight about equal to that of a kidney. They are especially abundant on the palms, soles, and forehead, but they are widely distributed over the rest of the body as well. Each is a simple tubular gland with a twisted coil in the dermis or hypodermis and an undulating or coiled duct leading to a sweat pore on the skin surface. This duct is lined by a stratified cuboidal epithelium in the dermis and by keratinocytes in the epidermis. Amid the secretory cells at the deep end of the gland, there are specialized myoep-ithelial29 cells with properties similar to smooth muscle. They contract in response to stimuli from the sympathetic nervous system and squeeze perspiration up the duct.

Sweat begins as a protein-free filtrate of the blood plasma produced by the deep secretory portion of the gland. Most sodium chloride is reabsorbed from this filtrate as the secretion passes through the duct. Potassium ions, urea, lactic acid, ammonia, and some sodium chloride remain in the sweat. Some drugs are also excreted in the perspiration. On average, sweat is 99% water and has a pH ranging from 4 to 6. Each day, the sweat glands secrete about 500 mL of insensible perspiration, which does not produce noticeable wetness of the skin. Under conditions of exercise or heat, however, a person may lose as much as a liter of perspiration each hour. In fact, so much fluid can be lost from the bloodstream by sweating as to cause circulatory shock. Sweating with visible wetness of the skin is called diaphoresis30 (DY-uh-foe-REE-sis).

Apocrine sweat glands occur in the groin, anal region, axilla, and areola, and in mature males, the beard area. They are absent from the axillary region of Koreans, however, and are sparse in the Japanese. Their ducts lead into nearby hair follicles rather than opening directly onto the skin surface (fig. 6.11fc). They produce their secretion in the same way that merocrine glands do—by exocytosis. The secretory part of an apocrine gland, however, has a much larger lumen than that of a merocrine gland, so these glands have continued to be referred to as apocrine glands to distinguish them functionally and histologically from the merocrine

Apocrine Merocrine Sweat Glands

Figure 6.11 Cutaneous Glands. (a) Merocrine sweat glands have a narrower lumen and a duct that opens by way of a pore on the skin surface. (b) Apocrine sweat glands have a large lumen and a duct that conveys their aromatic secretion into a hair follicle. (c) Sebaceous glands have cells that break down in entirety to form an oily secretion that is released into the hair follicle. Are apocrine glands associated with vellus or terminal hair? Explain.

Figure 6.11 Cutaneous Glands. (a) Merocrine sweat glands have a narrower lumen and a duct that opens by way of a pore on the skin surface. (b) Apocrine sweat glands have a large lumen and a duct that conveys their aromatic secretion into a hair follicle. (c) Sebaceous glands have cells that break down in entirety to form an oily secretion that is released into the hair follicle. Are apocrine glands associated with vellus or terminal hair? Explain.

Saladin: Anatomy & I 6. The Integumentary I Text I I © The McGraw-Hill

Physiology: The Unity of System Companies, 2003 Form and Function, Third Edition type. Apocrine sweat is thicker and more milky than mero-crine sweat because it has more fatty acids in it.

Apocrine sweat glands are scent glands that respond especially to stress and sexual stimulation. They do not develop until puberty, and they apparently correspond to the scent glands that develop in other mammals on attainment of sexual maturity. In women, they enlarge and shrink in phase with the menstrual cycle. Apocrine sweat does not have a disagreeable odor, and indeed it is considered attractive or arousing in some cultures, where it is as much a part of courtship as artificial perfume is to other people. Clothing, however, traps stale sweat long enough for bacteria to degrade the secretion and release free fatty acids with a rancid odor. Disagreeable body odor is called bromhidrosis.31 It occasionally indicates a metabolic disorder, but more often it reflects poor hygiene.

Many mammals have apocrine scent glands associated with specialized tufts of hair. In humans, apocrine glands are found mainly in the regions covered by the pubic hair, axillary hair, and beard. This suggests that like other mammalian scent glands, they serve to produce pheromones, chemicals that influence the physiology or behavior of other members of the species (see insight 16.1, p. 595). The hair serves to retain the aromatic secretion and regulate its rate of evaporation from the skin. Thus, it seems no mere coincidence that women's faces lack both apocrine scent glands and a beard. It has also been demonstrated that men's beards grow faster when they live in the presence of women than when they live apart from them.

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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Responses

  • sago
    What is bigger apocrine or merocrine sweat gland?
    6 years ago
  • barbara
    Which type of gland develops at puberty to respond to stress and sexual stimulation?
    4 years ago

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