Sebaceous gland: Difference between revisions
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Sebaceous glands are found in hair-covered areas, where they are connected to [[hair follicle]]s. One or more glands may surround each hair follicle, and the glands themselves are surrounded by the [[arrector pili muscle]]. The glands have an [[acinus|acinar structure]] similar to a bunch of grapes, in which multiple glands branch off a central duct. The glands deposit sebum on the hairs, and bring it to the skin surface along the hair shaft. The structure consisting of hair, hair follicle, arrector pili muscle, and sebaceous gland is an epidermal invagination known as a ''pilosebaceous unit''.<ref name= WHEATER2006/> |
Sebaceous glands are found in hair-covered areas, where they are connected to [[hair follicle]]s. One or more glands may surround each hair follicle, and the glands themselves are surrounded by the [[arrector pili muscle]]. The glands have an [[acinus|acinar structure]] similar to a bunch of grapes, in which multiple glands branch off a central duct. The glands deposit sebum on the hairs, and bring it to the skin surface along the hair shaft. The structure consisting of hair, hair follicle, arrector pili muscle, and sebaceous gland is an epidermal invagination known as a ''pilosebaceous unit''.<ref name= WHEATER2006/> |
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Sebaceous glands are also found in |
Sebaceous glands are also found in hairless areas ([[glabrous skin]]) of [[eyelid]]s, [[human nose|nose]], [[penis]], [[labia minora]], the inner membrane of the [[cheek]] and [[nipple]]s. There are sebaceous glands in the [[areola]] surrounding the nipple in the breast; volatile compounds secreted from the glands are thought to serve as an olfactory stimulus for the newborn.<ref>{{cite journal |doi=10.1371/journal.pone.0007579 |ref=harv |title=The Secretion of Areolar (Montgomery's) Glands from Lactating Women Elicits Selective, Unconditional Responses in Neonates |year=2009 |editor1-last=Hausberger |editor1-first=Martine |last1=Doucet |first1=Sébastien |last2=Soussignan |first2=Robert |last3=Sagot |first3=Paul |last4=Schaal |first4=Benoist |journal=PLoS ONE |volume=4 |issue=10 |pages=e7579 |pmid=19851461 |pmc=2761488}}</ref> During pregnancy and lactation these glands become enlarged. At the rim of the eyelids, [[meibomian gland]]s are a specialized form of sebaceous gland. They secrete a form of sebum called [[meibum]] onto the [[human eye|eye]], slowing the evaporation of [[tears]].<ref name= WHEATER2006/> |
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During pregnancy and lactation these glands become enlarged. At the rim of the eyelids, [[meibomian gland]]s are a specialized form of sebaceous gland. They secrete a form of sebum called [[meibum]] onto the [[human eye|eye]], slowing the evaporation of [[tears]].<ref name= WHEATER2006/> |
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===Development=== |
===Development=== |
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Revision as of 16:01, 5 April 2014
| Sebaceous gland | |
|---|---|
 Schematic view of hair follicle and sebaceous gland. | |
 Cross-section of all skin layers. A hair follicle with associated structures. (Sebaceous glands labeled at center left.) | |
| Details | |
| Identifiers | |
| Latin | glandula sebacea |
| MeSH | D012627 |
| TA98 | A16.0.00.030 A15.2.07.044 |
| TA2 | 7082 |
| FMA | 59160 |
| Anatomical terminology | |
The sebaceous glands are microscopic exocrine glands in the skin that secrete an oily or waxy matter, called sebum, to lubricate and waterproof the skin and hair of mammals.[1] In humans, they are found in the greatest number, on the face and scalp, and are also found on all parts of the skin except the palms of the hands and (foot)|soles of the feet.[2] The type of secretion of the sebaceous glands is referred to as holocrine.
In the eyelids, meibomian glands, also called tarsal glands, are a type of sebaceous gland that secrete a special type of sebum into tears. There are several related medical conditions, including acne, sebaceous cysts, hyperplasia and sebaceous adenoma.
Structure
Location
The sebaceous glands exist in humans throughout the skin except in the palms of the hands and soles of the feet. There are two types of sebaceous gland, those connected to hair follicles, and those that exist independent of hair follicles.[3]
Sebaceous glands are found in hair-covered areas, where they are connected to hair follicles. One or more glands may surround each hair follicle, and the glands themselves are surrounded by the arrector pili muscle. The glands have an acinar structure similar to a bunch of grapes, in which multiple glands branch off a central duct. The glands deposit sebum on the hairs, and bring it to the skin surface along the hair shaft. The structure consisting of hair, hair follicle, arrector pili muscle, and sebaceous gland is an epidermal invagination known as a pilosebaceous unit.[3]
Sebaceous glands are also found in hairless areas (glabrous skin) of eyelids, nose, penis, labia minora, the inner membrane of the cheek and nipples. There are sebaceous glands in the areola surrounding the nipple in the breast; volatile compounds secreted from the glands are thought to serve as an olfactory stimulus for the newborn.[4] During pregnancy and lactation these glands become enlarged. At the rim of the eyelids, meibomian glands are a specialized form of sebaceous gland. They secrete a form of sebum called meibum onto the eye, slowing the evaporation of tears.[3]
Development
The sebaceous glands of a human fetus secrete a substance called vernix caseosa, a waxy, translucent white substance coating the skin of newborns.
The activity of the sebaceous glands increases during puberty because of heightened levels of androgens, producing smegma. In males, sebaceous glands begin to appear predominantly on the penis, on the shaft and around the rim of the penile head during and after puberty. In females, they appear predominantly in the labia minora. These more visible glands are known as Fordyce spots which are also seen on the border of the inside of the lips of the mouth. They are completely natural and harmless.
Function
Sebum
Sebaceous glands secrete the oily, waxy substance called sebum (Latin: fat, tallow) that is made of triglyceride oils, wax, squalene, and metabolites of fat-producing cells.[5][6] Sebum is produced in a holocrine process, in which cells within the sebaceous gland disintegrate as they release the sebum. The cells are constantly replaced by mitosis at the base of the duct.[3]
Some hormones, including androgens such as testosterone and estrogen, as well as progesterone, increase the rate of sebum secretion.[7]
Immune function and nutrition
Sebaceous lipids contribute to maintaining the integrity of the skin barrier, and express pro-inflammatory and anti-inflammatory properties.[8][9][10] Recent research suggests that sebum may represent a delivery system for antioxidants, antimicrobial lipids, pheromones, and hydration of stratum corneum.[11] During the last gestation trimester, it is known that sebaceous glands produce vernix caseosa which protects the embryonic skin from amniotic water.[12] Sebaceous secretions in conjunction with apocrine glands also play an important thermoregulatory role. In hot conditions, the secretions emulsify and foment formation of and prevent the loss of sweat drops from the skin. In colder conditions, sebum repels rain from skin and hair.[10] Increased facial surface sebum secretion is also associated with the development of acne.[9]
Additionally, sebaceous gland secretion provides Vitamin E to the upper layers of facial skin.[13]
Sebum keeps hair and skin supple. Sebum is odorless, but its bacterial breakdown can produce odors. Sebum is the cause of some people's experiencing "oily" hair,[14] as in hot weather or if not washed for several days. Earwax is partly composed of sebum.
Sebaceous glands are part of the body's integumentary system and serve to protect the body against germs.
Composition
The composition of sebum varies across species. In humans, the lipid content is as follows:[15]
| Substance | Percent composition |
| triglycerides | 41% |
| wax monoesters | 25% |
| free fatty acids | 16% |
| squalene | 12% |
Sebum secreted by the sebaceous gland is primarily composed of tryglycerides, wax esters, and squalene.[16] Wax esters, like squalene, are unique to sebum and not produced anywhere else in the body.[17] Sebum also contains 45% water-insoluble fatty acids known to have broad antimicrobial activity.[11][18] Sapienic acid is a sebum fatty acid that is unique to humans. [citation needed]
Clinical significance
Sebaceous glands are involved in skin problems such as acne and keratosis pilaris. The demodex mite is implicated in the cause of acne.[19] The mite is also a cause of blepharitis (inflammation of the eyelids). In the skin pores, sebum and keratin can create a hyperkeratotic plug called a microcomedone.
Acne
Acne is a very common problem, particularly after puberty in teenagers, and is thought to relate to increased production of sebum due to hormonal factors, combined with an increased propensity to infection, particularly by the bacteria propionibacterium acnes. This is thought to occlude the duct of the sebaceous gland, leading to inflammation and the characteristic acne lesions. Lesions, known as comedomes, generally occur on the areas with more sebacious glands, particularly the face, shoulders, upper chest and back. Comedomes may be 'black' or 'white' depending on whether the entire pilosebaceous unit, or just the sebaceous duct, is blocked.[7]
When treated, acne is generally treated with antibiotics or isotretinoin.[7] Isotretinoin reduces the amount of sebum produced by the sebaceous glands.[20] A better treatment is claimed for SMT D002.[21] Another treatment seen to be effective in females is Spironolactone[22]
Other
Other conditions that affect the sebaceous glands include:
- Sebaceous hyperplasia, enlargement of the glands.
- Seborrhoeic dermatitis, a severe form of dermatitis effected by changes in the sebaceous glands.
- Sebaceous adenoma, a benign slow-growing tumour which may however in rare cases be a precursor to a cancer syndrome known as Muir-Torre syndrome.
- Sebaceous carcinoma, an uncommon and aggressive cutaneous tumour.[23]
- Sebaceous cyst is a term used to refer to both an epidermoid cyst and a pilar cyst, though neither of these contain sebum, only keratin and do not originate in the sebaceous gland and so are not true sebaceous cysts. A true sebaceous cyst is relatively rare and is known as a steatocystoma.
Other animals
Many animals, including fish, have sebaceous glands. In birds the glands are located at the base of the tail, which also supplies oil that is spread upon the feathers during preening.
Ductless glands in fish, are situated internally and are not true oil glands, however, fishermen will often cleanse bottom-feeding fish such as carp by removing an internal organ (which is said to be "the oil gland"). Ductless internal organs are called "glands," as well. Having no ducts, they tend to store substances which give a disagreeable taste to a cooked fish. Removing the oil gland from a carp prior to cooking removes some of the accumulated substances, some of which may also be toxic or harmful.
The preputial glands of mice and rats are large modified sebaceous glands that produce pheromones.
Sebaceous adenitis is an autoimmune disease affecting the sebaceous gland, known mainly to occur in canines.
History
The word sebaceous – secreting sebum, was first termed in 1728 and comes from the Latin for tallow.[24]
Additional images
-
Base of pilosebaceous unit -
Insertion of sebaceous glands into hair shaft -
Sagittal section through the upper eyelid. -
A hair follicle with associated structures.
See also
References
- ^ Dellmann's textbook of veterinary histology (405 pages), Jo Ann Coers Eurell, Brian L. Frappier, 2006, p.29, weblink: Books-Google-RTOC.
- ^ James, William D.; Berger, Timothy; Elston, Dirk M. (2006). Andrews' diseases of the skin: clinical dermatology. Saunders Elsevier. p. 7. ISBN 978-0-7216-2921-6.
- ^ a b c d Deakin, Barbara Young ... ; drawings by Philip J.; et al. (2006). Wheater's functional histology : a text and colour atlas (5th ed. ed.). [Edinburgh?]: Churchill Livingstone/Elsevier. pp. 175–178, 413. ISBN 978-0-443-068-508.
{{cite book}}:|edition=has extra text (help); Explicit use of et al. in:|first=(help)CS1 maint: multiple names: authors list (link) - ^ Doucet, Sébastien; Soussignan, Robert; Sagot, Paul; Schaal, Benoist (2009). Hausberger, Martine (ed.). "The Secretion of Areolar (Montgomery's) Glands from Lactating Women Elicits Selective, Unconditional Responses in Neonates". PLoS ONE. 4 (10): e7579. doi:10.1371/journal.pone.0007579. PMC 2761488. PMID 19851461.
{{cite journal}}: Invalid|ref=harv(help)CS1 maint: unflagged free DOI (link) - ^ "Exercise 15: Hair", VT.edu, 2008, webpage: Vetmed-lab15.
- ^ Lampe, M.A. (1983). "Human stratum corneum lipids: characterization and regional variations". J. Lipid Res. 24: 120–130.
{{cite journal}}:|access-date=requires|url=(help); Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ a b c Britton, the editors Nicki R. Colledge, Brian R. Walker, Stuart H. Ralston ; illustated by Robert (2010). Davidson's principles and practice of medicine (21st ed. ed.). Edinburgh: Churchill Livingstone/Elsevier. pp. 1267–1268. ISBN 978-0-7020-3085-7.
{{cite book}}:|edition=has extra text (help);|first=has generic name (help)CS1 maint: multiple names: authors list (link) - ^ "Why do we have apocrine and sebaceous glands?". 10/5/2011. PMC 1281456.
{{cite web}}: Check date values in:|date=(help); Missing or empty|url=(help) - ^ a b Youn, S. W. (2010). "The Role of Facial Sebum Secretion in Acne Pathogenesis: Facts and Controversies". Clinics in Dermatology. 28 (1): 8–11. doi:10.1016/j.clindermatol.2009.03.011. PMID 20082943.
- ^ a b Zouboulis, C. C. (2004). "Acne and Sebaceous Gland Function". Clinics in Dermatology. 22 (5): 360–366. doi:10.1016/j.clindermatol.2004.03.004. PMID 15556719.
- ^ a b Mackenna, R. M. B.; Wheatley, V. R.; Wormall, A. (1950). "The Composition of the Surface Skin Fat ('Sebum') from the Human Forearm". Journal of Investigative Dermatology. 15 (1): 33–47. doi:10.1038/jid.1950.69. PMID 14774573.
- ^ Zouboulis, Christos C.; et al. , Jens Malte; et al. (2008). "Frontiers in Sebaceous Gland Biology and Pathology". Experimental Dermatology. 17 (6): 542–551. doi:10.1111/j.1600-0625.2008.00725.x. PMID 18474083.
- ^ Thiele, Jens J.; Weber, Stefan U.; Packer, Lester (1999). "Sebaceous Gland Secretion is a Major Physiologic Route of Vitamin E Delivery to Skin". Journal of Investigative Dermatology. 113 (6): 1006–1010. doi:10.1046/j.1523-1747.1999.00794.x. PMID 10594744.
- ^ "Hair Care: An Illustrated Dermatologic Handbook", Zoe Diana Draelos, Zoe Kececioglu Draelos, 2005, p.26, web: Books-Google-5QC: oily hair & detergents.
- ^ Cheng JB, Russell DW (September 2004). "Mammalian Wax Biosynthesis: II. EXPRESSION CLONING OF WAX SYNTHASE cDNAs ENCODING A MEMBER OF THE ACYLTRANSFERASE ENZYME FAMILY" (PDF). The Journal of Biological Chemistry. 279 (36): 37798–807. doi:10.1074/jbc.M406226200. PMC 2743083. PMID 15220349.
{{cite journal}}: CS1 maint: unflagged free DOI (link) - ^ Thody, A. J.; Shuster, S. (1989). "Control and Function of Sebaceous Glands". Physiological Reviews. 69 (2): 383–416. PMID 2648418.
- ^ Smith, K. R.; Thiboutot, D. M. (2007). "Thematic Review Series: Skin Lipids. Sebaceous Gland Lipids: Friend Or Foe?". Journal of Lipid Research. 49 (2): 271–281. doi:10.1194/jlr.R700015-JLR200. PMID 17975220.
{{cite journal}}: CS1 maint: unflagged free DOI (link) - ^ "Thematic Review Series: Skin Lipids. Antimicrobial lipids at the skin surface". 10/5/2011.
{{cite web}}: Check date values in:|date=(help) - ^ Ya-e Zhao; et al. (2012). "A meta-analysis of association between acne vulgaris and Demodex infestation". Journal of Zhejiang University-SCIENCE B. 13 (3): 192–202. doi:10.1631/jzus.B1100285. PMC 3296070. PMID 22374611.
{{cite journal}}: Explicit use of et al. in:|author=(help) - ^ Farrell LN, Strauss JS, Stranieri AM (December 1980). "The treatment of severe cystic acne with 13-cis-retinoic acid. Evaluation of sebum production and the clinical response in a multiple-dose trial". Journal of the American Academy of Dermatology. 3 (6): 602–11. doi:10.1016/S0190-9622(80)80074-0. PMID 6451637.
{{cite journal}}: CS1 maint: multiple names: authors list (link) - ^ http://www.summitplc.com/uploads/RNSSeborrhoeatrialFINAL.pdf
- ^ Goodfellow A; Alaghband-Zadeh J; Carter G; et al. (August 1984). "Oral spironolactone improves acne vulgaris and reduces sebum excretion". The British Journal of Dermatology. 111 (2): 209–14. doi:10.1111/j.1365-2133.1984.tb04045.x. PMID 6235834.
{{cite journal}}: Unknown parameter|author-separator=ignored (help) - ^ Nelson BR, Hamlet KR, Gillard M, Railan D, Johnson TM (July 1995). "Sebaceous carcinoma". J. Am. Acad. Dermatol. 33 (1): 1–15, quiz 16–8. doi:10.1016/0190-9622(95)90001-2. PMID 7601925.
{{cite journal}}: CS1 maint: multiple names: authors list (link) - ^ Harper, Douglas. "Sebaceous". Etymology Online. Retrieved 5 April 2014.
External links
- Histology image: 08801loa – Histology Learning System at Boston University - "Integument: scalp"
- Sebaceous+Glands at the U.S. National Library of Medicine Medical Subject Headings (MeSH)