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Apocrine sweat gland

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An apocrine sweat gland (/ˈæpəkrən, -ˌkraɪn, -ˌkriːn/; from Greek apo 'away' and krinein 'to separate')[5][6] is composed of a coiled secretory portion located at the junction of the dermis and subcutaneous fat, from which a straight portion inserts and secretes into the infundibular portion of the hair follicle.[7] In humans, apocrine sweat glands are found only in certain locations of the body: the axillae (armpits), areola and nipples of the breast, ear canal, eyelids, wings of the nostril, perineal region, and some parts of the external genitalia.[8] Modified apocrine glands include the ciliary glands (glands of Moll) in the eyelids; the ceruminous glands, which produce ear wax; and the mammary glands, which produce milk.[3] They are distinct from eccrine sweat glands, which cover the whole body.[9]

Apocrine sweat gland
Microscopic photography of eccrine and apocrine sweats glands in dermis.
Details
PrecursorPrimary epithelial germ[4]
SystemIntegumentary system[2]
NerveAdrenergic nerves[3]
Identifiers
Latinglandula sudorifera apocrina[1]
MeSHD001050
THH3.12.00.3.03002
FMA59155
Anatomical terminology

Most non-primate mammals, however, have apocrine sweat glands over the greater part of their body.[8] Domestic animals such as dogs and cats have apocrine glands at each hair follicle and even in their urinary system, but eccrine glands only in foot pads and snout. Their apocrine glands, like those in humans, produce an odorless, oily, opaque secretion[10] that gains its characteristic odor upon bacterial decomposition.[11] Eccrine glands on their paws increase friction and prevent them from slipping when fleeing from danger.[12]

Structure

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The apocrine gland is made up of a glomerulus of secretory tubules and an excretory duct that opens into a hair follicle;[13] on occasion, an excretory duct opens to the skin surface next to the hair.[14] The gland is large and spongy, located in the subcutaneous fat deep in the dermis,[9][15] and has a larger overall structure and lumen diameter than the eccrine sweat gland.[16][8] The secretory tubules of apocrine glands are single layered, but unlike the eccrine secretory tubules, contain only a single type of ductal epithelial cell,[17] varying in diameter according to their location, and sometimes branching off into multiple ducts. The tubules are wrapped in myoepithelial cells, which are more developed than in their eccrine gland counterparts.[18][19]

Sweating

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In hoofed animals and marsupials, apocrine glands act as the main thermoregulator, secreting watery sweat.[9] For most mammals, however, apocrine sweat glands secrete an oily (and eventually smelly) compound that acts as a pheromone,[20] territorial marker, and warning signal.[10][21][22] Being sensitive to adrenaline, apocrine sweat glands are involved in emotional sweating in humans (induced by anxiety, stress, fear, sexual stimulation, and pain).[21]

In a five-month-old human fetus, apocrine glands are distributed all over the body; after a few weeks, they exist in only restricted areas,[9] including the armpits and external genitalia.[8] They are inactive until stimulated by hormonal changes in puberty.[21]

Mechanism

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The apocrine gland secretes an oily fluid with proteins and lipids that is odorless before microbial activity. It appears on the skin surface mixed with sebum, as sebaceous glands open into the same hair follicle.[23] Unlike eccrine sweat glands, which secrete continuously, the apocrine glands secrete in periodic spurts.[20]

Apocrine sweat glands were originally thought to use only apocrine secretion: vesicles pinch off from the secretory cells, then degrade in the secretory lumen, releasing their product.[24] More recent research has shown that merocrine secretion also takes place.[25]

Myoepithelial cells form a smooth muscle lining around the secretory cells; when the muscles contract, they squeeze the secretory ducts and push out the accumulated fluid into the hair follicle.[20][26] Sweat and sebum are mixed in the hair follicle and arrive mixed at the epidermal surface.[9] The apocrine sweat is cloudy, viscous, initially odorless, and at a pH of 6–7.5. It contains water, protein, carbohydrate waste material, and NaCl.[27] The sweat only attains its characteristic odor upon being degraded by bacteria, which releases volatile odor molecules.[23] More bacteria (especially corynebacteria) leads to stronger odor. The presence of axillary hair also makes the odor even more pungent, as secretions, debris, keratin, and bacteria accumulate on the hairs.[15]

Prevalence

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Non-primate mammals usually have apocrine sweat glands over most of their bodies.[8] Horses use them as a thermoregulatory device, as they are regulated by adrenaline and more widely distributed on equines than in other groups.[28] Skunks, on the other hand, use the glands to release a secretion that acts as a powerful defense mechanism.[20]

The "axillary organs", limited regions with equal numbers of apocrine and eccrine sweat glands, only exist in humans, gorillas, and chimpanzees.[9] In humans, the apocrine glands in this region are the most developed (with the most complex glomeruli).[18] Men have more apocrine sweat glands than women in all axillary regions.[29][30]

There is currently no evidence that any sweat glands vary substantially by racial group, with most studies claiming to find variation being subject to methodological flaws.[31]

See also

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References

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Citations

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  1. ^ H3.12.00.3.03002
  2. ^ Neas, John F. "Development of the Integumentary System". In Martini, Frederic H.; Timmons, Michael J.; Tallitsch, Bob (eds.). Embryology Atlas (4th ed.). Benjamin Cumings. Archived from the original on 8 August 2012. Retrieved 17 December 2012.
  3. ^ a b Krstic 2004, p. 466.
  4. ^ Tsai 2006, p. 496.
  5. ^ McKean, Erin (2005). "apocrine". The New Oxford American Dictionary (2 ed.). ISBN 9780195170771.
  6. ^ McKean, Erin (2005). "apo-". The New Oxford American Dictionary (2 ed.). ISBN 9780195170771.
  7. ^ Elston, William D.; James, Timothy G.; Berger, Dirk M. (2006). Andrew's Diseases of the Skin: Clinical Dermatology (10th ed.). Philadelphia: Saunders Elsevier. p. 7. ISBN 9780808923510.
  8. ^ a b c d e Kurosumi, Shibasaki & Ito 1984, p. 255.
  9. ^ a b c d e f Edgar Folk Jr, G.; Semken Jr, A. (1 September 1991). "The evolution of sweat glands". International Journal of Biometeorology. 35 (3): 180–6. Bibcode:1991IJBm...35..180F. doi:10.1007/BF01049065. ISSN 0020-7128. PMID 1778649. S2CID 28234765.
  10. ^ a b "Cutaneous Apocrine Gland Tumors". The Merck Veterinary Manual. Merck Sharp & Dohme Corp. Archived from the original on 2016-03-04.
  11. ^ Eroschenko 2008, pp. 228–229.
  12. ^ Wilke et al. 2007, p. 170.
  13. ^ Kurosumi, Shibasaki & Ito 1984, pp. 255–256.
  14. ^ Tsai 2006, pp. 496–497.
  15. ^ a b Tsai 2006, p. 497.
  16. ^ Krstic 2004, p. 468.
  17. ^ Bolognia, Jean; Jorizzo, Joseph L.; Schaffer, Julie V. (2012). Dermatology. Structure and Function of Eccrine, Apocrine and Sebaceous Glands (3rd ed.). pp. 539–544. ISBN 978-0723435716.
  18. ^ a b Kurosumi, Shibasaki & Ito 1984, p. 256.
  19. ^ Eroschenko 2008, p. 226.
  20. ^ a b c d Spearman, Richard Ian Campbell (1973). The Integument: A Textbook For Skin Biology. Biological Structure and Function Books. Vol. 3. CUP Archive. p. 137. ISBN 9780521200486.
  21. ^ a b c Wilke et al. 2007, p. 171.
  22. ^ Jordania, Joseph (2011). Why do People Sing? Music in Human Evolution. Tbilisi, Georgia: Logos. pp. 123–124. ISBN 9789941401862.
  23. ^ a b Wilke et al. 2007, p. 175.
  24. ^ "sweat gland". Miller-Keane Encyclopedia & Dictionary of Medicine, Nursing, and Allied Health (7th ed.). Saunders. 2003. Retrieved 18 December 2012.
  25. ^ Henrikson, Ray C.; Kaye, Gordon I.; Mazurkiewicz, Joseph E. (1 July 1997). NMS Histology (3rd ed.). Lippincott Williams & Wilkins. p. 234. ISBN 9780683062250.
  26. ^ Martini, Frederic (2005). Anatomy and Physiology' 2007. Rex Bookstore, Inc. p. 122. ISBN 9789712348075.
  27. ^ Draelos, Zoe Diana (2010). "Prevention of Cosmetic Problems". In Norman, R. A. (ed.). Preventive Dermatology. Springer. p. 182. doi:10.1007/978-1-84996-021-2_16. ISBN 9781849960267.
  28. ^ Caceci, Thomas. "Integument I: Skin". VM8054 Veterinary Histology Laboratory Exercises. Virginia–Maryland Regional College of Veterinary Medicine. Archived from the original on 13 May 2015. Retrieved 19 December 2012.
  29. ^ Wilke et al. 2007, p. 174.
  30. ^ Stoddart 1990, p. 60.
  31. ^ Taylor, Susan C. (1 February 2002). "Skin of color: Biology, structure, function, and implications for dermatologic disease". Journal of the American Academy of Dermatology. 46 (2, Supplement 2): S41–S62. doi:10.1067/mjd.2002.120790. PMID 11807469.

Sources

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