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| Sweat gland |
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| A. Epidermis
B. Dermis C. Subcutis/Hypodermis D. Blood and Lymph Vessels E. Stratum Germinativum
1. Hair Shaft 2. Stratum Corneum 3. Pigment Layer 4. Stratum Spinosum 5. Stratum Basale 6. Arrector Pili Muscle 7. Sebaceous Gland 8. Hair Follicle 9. Papilla of Hair 10. Nerve Fiber 11. Sweat Gland 12. Pacinian Corpuscle 13. Artery 14. Vein 15. Sensory Nerve ending (for touch) 16. Dermal Papillary 17. Sweat Pore
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| MeSH |
Sweat+glands |
Sweat glands, or sudoriferous glands, are small tubular structures of the skin that produce sweat. There are two kinds of sweat glands:
- Eccrine sweat glands are found only in primates and reach their greatest development in humans. They are distributed all over the body (except for the lips, tip of penis and clitoris) although their density varies from region to region. Humans utilize eccrine sweat glands as primary form of cooling. The human thermal eccrine system has evolved in concert with bipedalism and development of smooth hairless skin.[1]
- Apocrine sweat glands are larger, have different mechanism of secretion, and are limited to axilla (armpits) and perianal areas in humans. Although apocrine glands contribute little to cooling in humans, they are the only effective sweat glands in hoofed animals such as the donkey, cow, horse, and camel.[2][3] Most other mammals, such as cats, dogs and pigs, rely on panting or other means for thermal regulation.
Domestic animals have apocrine glands at the base of each hair follicle but eccrine glands only in foot pads and snout. Their apocrine glands, like those in humans, produce an odorless oily milky secretion evolved not to evaporate and cool but rather coat and stick to hair so odor-causing bacteria can grow on it. [4] Eccrine glands on their foot pads, like those on palms and soles of humans, didn't evolve to cool either but rather increase friction and enhance grip.
Both apocrine and eccrine sweat glands contain myoepithelial cells (from Greek myo-, "muscle"), specialized epithelial cells located between the gland cells and the underlying basal lamina. Myoepithelial cell contractions squeeze the gland and discharge the accumulated secretions. The secretory activities of the gland cells and the contractions of myoepithelial cells are controlled by both the autonomic nervous system and by the circulating hormones.
Ceruminous glands, which produce ear wax, and mammary glands, which produce milk, are frequently considered to be modified sweat glands, but they are not. Both ceruminous and mammary glands are true apocrine glands.[5]
Apocrine sweat glands
The name apocrine was originally chosen because it was believed that the gland cells used an apocrine method of secretion. Although it is now known that their secretory products are produced through merocrine secretion, the name has not changed. Apocrine sweat glands are coiled tubular glands that produce a viscous, cloudy and potentially odorous secretion. Apocrine sweat glands discharge in the canals of hair follicles. They begin secreting at puberty; the sweat produced may be acted upon by bacteria, causing a noticeable odor. Apocrine gland secretions may also contain pheromones, chemicals that communicate information to other individuals by altering their hormonal balance. Some research has indicated that feminine secretions from apocrine sweat glands can alter the menstrual timing of other women (this is called the McClintock effect), though the research methods used have been criticized. The significance of human pheromones and the role of apocrine sweat gland secretions in humans remains incompletely understood.
Eccrine sweat glands
Eccrine sweat glands are smaller than apocrine sweat glands, and they do not extend as deep into the dermis. Eccrine sweat glands are coiled tubular glands that discharge their secretions directly onto the surface of the skin. Their density varies greatly according to body regions, the highest density (>250 glands/cm2) being on soles, palms, and scalp.
The clear secretion produced by eccrine sweat glands is termed sweat or sensible perspiration. Sweat is mostly water, but it does contain some electrolytes, since it is derived from blood plasma, although less concentrated. It therefore contains mainly sodium chloride, but also other electrolytes. The presence of sodium chloride gives sweat a salty taste. The total volume of sweat produced depends on the number of functional glands and the size of the surface opening. The degree of secretory activity is regulated by neural and hormonal mechanisms (men produce greater volumes of sweat than women). When all of the eccrine sweat glands are working at maximum, the rate of perspiration for a human being may exceed three liters per hour,[6] and dangerous fluid and electrolyte losses can occur.
Eccrine glands have three primary functions:
- Thermoregulation. Sweat cools the surface of the skin and reduces body temperature.
- Excretion. Eccrine sweat gland secretion can also provide a significant excretory route for water and electrolytes.[citation needed].
- Protection. Eccrine sweat gland secretion aids in preserving the skin's acid mantle, which helps protect the skin from colonisation from bacteria and other pathogenic organisms.[7]
References
- ^ G. Edgar Folk Jr. and A. Semken Jr. (1991). "The evolution of sweat glands". Int. J. Of Biometeorology 35 (3): 180–186. doi:10.1007/BF01049065. PMID 1778649. http://www.springerlink.com/content/r25946621680811l/.
- ^ Bullard RW, Dill DB, Yousef MK (1970). "Responses of the burro to desert heat stress". J Appl Physiol 29 (2): 159–167. PMID 5428889. http://jap.physiology.org/content/29/2/159.extract.
- ^ Sorensen VW, Prasad G (1973). "On the fine structure of horse sweat glands". Z Anat Entwicklungsgesch. 139 (2): 173–183. doi:10.1007/BF00523636. PMID 4352229. http://www.springerlink.com/content/m3103x6v14300160/.
- ^ Cutaneous Apocrine Gland Tumors - The Merck Veterinary Manual
- ^ Ackerman, A. Bernard; Almut Böer, Bruce Bennin, and Geoffrey J. Gottlieb (2005). Histologic Diagnosis of Inflammatory Skin Diseases An Algorithmic Method Based on Pattern Analysis. ISBN 978-1-893357-25-9. http://www.derm101.com/content/13501.
- ^ C.P. Hickman, L.S. Roberts and A. Larson (2001). Integrated Principles of Zoology, 11/e.
- ^ Marples, Mary J (1965). The ecology of the human skin. OL5915977M.
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Integumentary system (TA A16, TH H3.12, GA 10.1062)
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| Skin |
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Epidermis
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Stratum corneum · Stratum lucidum · Stratum granulosum · Stratum spinosum · Stratum basale
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Basement membrane zone
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Basal keratinocyte · Lamina lucida · Lamina densa
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Dermis
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Papillary (Dermal papillae) · Reticular
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| Subcutaneous tissue |
Panniculus/Pannus (Panniculus adiposus · Panniculus carnosus) · Stratum membranosum · Loose connective tissue · Superficial fascia
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| Adnexa |
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Skin glands
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Sweat glands: Apocrine sweat gland · Eccrine sweat gland
Sebaceous
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Hair
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Root sheath
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Outer root sheath · Inner root sheath (Henle's layer, Huxley's layer)
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Hair shaft
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Cuticle · Cortex · Medulla · Bulb with matrix cells · Hair follicle
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Muscle
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Arrector pili muscle
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Pilosebaceous unit
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Hair sebaceous gland
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Nail
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Nail matrix · Nail plate (Lunula) · Eponychium · Paronychium · Hyponychium
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noco(i/b/d/q/u/r/p/m/k/v/f)/cong/tumr(n/e/d), sysi/epon
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proc, drug (D2/3/4/5/8/11)
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noco/cong/tumr, sysi/epon
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