Apocrine sweat gland

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Apocrine sweat gland
Latin Glandula sudorifera apocrina[1]
System Integumentary system[2]
Nerve Adrenergic nerves[3]
Precursor Primary epithelial germ[4]
MeSH Apocrine+Glands
Code TH H3.12.00.3.03002

An apocrine sweat gland (/ˈæpəkrən/, /ˈæpəˌkrn/, or /ˈæpəˌkrin/, from Greek apo– "away" and krinein "to separate")[5][6] is a sweat gland 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, perianal region, and some parts of the external genitalia.[8] Modified apocrine glands include the ciliary glands in the eyelids; the ceruminous glands, which produce ear wax; and the mammary glands, which produce milk.[3] The rest of the body is covered by eccrine sweat glands.[9]

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 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[edit]

The apocrine gland comprises a glomerulus of secretory tubules and an excretory duct that opens into 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] Unlike eccrine secretory tubules, secretory tubules of the apocrine gland are single-layered (lacking ductal cells),[15] vary in diameter from place to place, and sometimes branch off into multiple ducts. The tubules are wrapped in myoepithelial cells, which are more developed than their eccrine gland counterparts.[17][18]

Sweating[edit]

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,[19] territorial marker, and warning signal.[10][20][21] Being sensitive to adrenaline, apocrine sweat glands are involved in emotional sweating in humans (induced by anxiety, stress, fear, sexual stimulation, and pain).[20]

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.[20]

Mechanism[edit]

The apocrine gland secretes an oily fluid with proteins, lipids, and steroids that is odorless before microbial activity. It appears on the skin surface mixed with sebum, as sebaceous glands open into the same hair follicle.[22] Unlike eccrine sweat glands, which secrete continuously, the apocrine glands secrete in periodic spurts.[19]

Apocrine sweat glands were originally thought to use only apocrine secretion: vesicles pinch off the secretory cells, then degrade in the secretory lumen, releasing their product.[23] More recent research has also shown that merocrine secretion takes place.[24]

Myoepithelial cells form a smooth muscle lining around the secretory cells; when the muscle contracts, they squeeze the secretory ducts and push out the accumulated fluid into the hair follicle.[19][25] 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.[26] The sweat only attains its characteristic odor upon being degraded by bacteria, which releases volatile odor molecules.[22] More bacteria (especially corynebacteria) leads to stronger odor. The presence of axillary hair also makes the odor worse, as secretions, debris, keratin, and bacteria accumulate on the hairs.[15]

Prevalence[edit]

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 on other groups.[27] Skunks, on the other hand, use the glands to release a stench that acts as a defense mechanism.[19]

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).[17] Men have more apocrine sweat glands than women in all axillary regions.[28][29]

See also[edit]

Notes[edit]

  1. ^ Federative International Committee on Anatomical Terminology (2008). Terminologia histologica: international terms for human cytology and histology. Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins. p. 121. ISBN 9780781775373. 
  2. ^ Neas, John F. "Development of the Integumentary System". In Martini, Frederic H.; Timmons, Michael J.; Tallitsch, Bob. Embryology Atlas (4th ed.). Benjamin Cumings. Retrieved 17 December 2012. 
  3. ^ a b Krstic 2004, p. 466.
  4. ^ Tsai 2006, p. 496.
  5. ^ "apocrine". The New Oxford American Dictionary (2 ed.). 2005. ISBN 9780195170771. 
  6. ^ "apo-". The New Oxford American Dictionary (2 ed.). 2005. ISBN 9780195170771. 
  7. ^ James, William D.; Berger; Elston, 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): 181. doi:10.1007/BF01049065. ISSN 0020-7128. Retrieved 18 December 2012. 
  10. ^ a b Merck Sharp & Dohme Corp. "Cutaneous Apocrine Gland Tumors". The Merck Veterinary Manual. 
  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 c Tsai 2006, p. 497.
  16. ^ Krstic 2004, p. 468.
  17. ^ a b Kurosumi, Shibasaki & Ito 1984, p. 256.
  18. ^ Eroschenko 2008, p. 226.
  19. ^ a b c d Spearman, Richard Ian Campbell (1973). The Integument: A Textbook For Skin Biology. Biological Structure and Function Books 3. CUP Archive. p. 137. ISBN 9780521200486. 
  20. ^ a b c Wilke et al. 2007, p. 171.
  21. ^ Jordania, Joseph (2011). Why do People Sing? Music in Human Evolution. Tbilisi, Georgia: Logos. pp. 123–124. ISBN 9789941401862. 
  22. ^ a b Wilke et al. 2007, p. 175.
  23. ^ "sweat gland". Miller-Keane Encyclopedia & Dictionary of Medicine, Nursing, and Allied Health (7th ed.). Saunders. 2003. Retrieved 18 December 2012. 
  24. ^ Henrikson, Ray C.; Kaye, Gordon I.; Mazurkiewicz, Joseph E. (1 July 1997). NMS Histology (3rd ed.). Lippincott Williams & Wilkins. p. 234. ISBN 9780683062250. 
  25. ^ Martini, Frederic. Anatomy and Physiology' 2007. Rex Bookstore, Inc. p. 122. ISBN 9789712348075. 
  26. ^ Draelos, Zoe Diana (2010). "Prevention of Cosmetic Problems". In Norman, R. A. Preventitive Dermatology. Springer. p. 182. doi:10.1007/978-1-84996-021-2_16. ISBN 9781849960267. 
  27. ^ Caceci, Thomas. "Integument I: Skin". VM8054 Veterinary Histology Laboratory Exercises. Virginia–Maryland Regional College of Veterinary Medicine. Retrieved 19 December 2012. 
  28. ^ Wilke et al. 2007, p. 174.
  29. ^ Stoddart 1990, p. 60.

References[edit]

  • Eroschenko, Victor P. (2008). "Integumentary System". DiFiore's Atlas of Histology with Functional Correlations. Lippincott Williams & Wilkins. pp. 212–234. ISBN 9780781770576. 
  • Krstic, Radivoj V. (18 March 2004). Human Microscopic Anatomy: An Atlas for Students of Medicine and Biology. Springer. pp. 464, 466–469. ISBN 9783540536666. 
  • Kurosumi, Kazumasa; Shibasaki, Susumu; Ito, Toshiho (1984). "Cytology of the Secretion in Mammalian Sweat Glands". In Bourne, Geoffrey H.; Danielli, James F. Protein Diffusion in Cell Membranes: Some Biological Implications. Orlando, Florida: Academic Press. pp. 253–330. ISBN 9780123644879. 
  • Stoddart, D. Michael (1990). The scented ape: The biology and culture of human odour. Cambridge: Cambridge University Press. pp. 60–61. ISBN 0521375118. 
  • Tsai, Ren-Yu (1 January 2006). "Treatment of Excessive Axillary Sweat Syndrome (Hyperhidrosis, Osmidrosis, Bromhidrosis) with Liposuction". In Shiffman, Melvin A.; Di Giuseppe, Alberto. Liposuction: Non-Cosmetic Applications. Germany: Springer. pp. 496–497. ISBN 9783540280439. 
  • Wilke, K.; Martin, A.; Terstegen, L.; Biel, S. S. (June 2007). "A short history of sweat gland biology" (pdf). International journal of cosmetic science 29 (3): 169–179. doi:10.1111/j.1467-2494.2007.00387.x. ISSN 1468-2494. 

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