Download Sebaceous gland - Saylor Academy

Sebaceous gland
1
Sebaceous gland
Sebaceous gland
Schematic view of hair follicle & sebaceous gland.
Cross-section of all skin layers. A hair follicle with associated structures. (Sebaceous glands labeled at center left.)
Latin
glandula sebacea
Gray's
subject #234 1069
MeSH
Sebaceous+glands
[1]
[2]
The sebaceous glands are microscopic glands in the skin which secrete an oily/waxy matter, called sebum, to
lubricate the skin and hair of mammals.[3] In humans, they are found in greatest abundance on the face and scalp,
though they are distributed throughout all skin sites except the palms and soles.[4] In the eyelids, meibomian
sebaceous glands secrete a special type of sebum into tears. There are several related medical conditions, including:
acne, sebaceous cysts, hyperplasia, sebaceous adenoma and sebaceous gland carcinoma (see section below:
Pathology).
Locations and morphology
A branched type of acinar gland, the sebaceous glands exist in humans throughout the skin except in the palms of the
hands and soles of the feet.
Sebaceous glands can usually be found in hair-covered areas, where they are connected to hair follicles (see image at
top). 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 known as a pilosebaceous unit.
Sebaceous glands are also found in non-haired areas (glabrous skin) of eyelids, nose, penis, labia minora, and
nipples. Here, the sebum traverses ducts which terminate in sweat pores on the surface of the skin.
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.
Sebaceous gland
2
Sebum
Sebaceous glands secrete the oily, waxy substance called sebum (Latin, meaning fat or tallow) that is made of fat
(lipids), wax, and the debris of dead fat-producing cells.[5] In the glands, sebum is produced within specialized cells
and is released as these cells burst; sebaceous glands are thus classified as holocrine glands.
Sebum is odorless, but its bacterial breakdown can produce odors. Sebum is the cause of some people experiencing
"oily" hair,[6] as in hot weather or if not washed for several days. Earwax is partly composed of sebum. Excess
sebum has been linked to eating red meats, fried, oily or other foods, but studies are not conclusive.
Function
Although it is commonly believed that sebum acts to protect and waterproof hair and skin, scientists have contended
that "low levels of sebaceous gland activity are not correlated with dry skin" and it may serve little or no purpose in
modern humans.[7]
Composition
The composition of sebum varies between species. In humans, the lipid content is as follows:[8]
Percent composition Substance
25%
wax monoesters
41%
triglycerides
16%
free fatty acids
12%
squalene
Sapienic acid is a sebum fatty acid that is unique to humans.
Control
The following treatments have been shown to reduce sebum secretion rates:
• Isotretinoin[9]
• SMT D002[10]
• Spironolactone[11] (suitable for females only)
Changes during development
The sebaceous glands of a human fetus in utero secrete a substance called Vernix caseosa, a "waxy" or "cheesy"
white substance coating the skin of newborns.
The activity of the sebaceous glands increases during puberty because of heightened levels of androgens. 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. This is however normal, not to be confused with an STD. In females, they appear
predominantly in the labia minora.
Sebaceous gland
3
Pathology
Sebaceous glands are involved in skin problems such as acne and keratosis pilaris. In the skin pores, sebum and
keratin can create a hyperkeratotic plug called a "microcomedone". The prescription drug isotretinoin significantly
reduces the amount of sebum produced by the sebaceous glands, and is used to treat acne.
The extreme use (up to 10 times doctor-prescribed amounts) of anabolic steroids by bodybuilders, for muscle gain
can cause acne. The sebaceous gland is stimulated due to some steroids conversion into dihydrotestosterone. This
may cause serious acne on the face, neck, chest, back and shoulders.
A blocked sebaceous gland can result in a sebaceous cyst.
A condition involving enlarged sebaceous glands is known as sebaceous hyperplasia.
Sebaceous gland carcinoma is a rare and aggressive form of cancer involving the sebaceous glands; sebaceous
adenoma is a more benign neoplasm of the sebaceous glands.
Sebum can also build up around body piercings.[12]
Importance to other animals
Certain species of Demodex mites feed on sebum and are commonly
found in the sebaceous glands of mammals, including those of humans.
The preputial glands of mice and rats are large modified sebaceous
glands that produce pheromones.
Demodex mite
Additional images
Pilosebaceous unit
Base of pilosebaceous unit
Insertion of sebaceous glands into hair shaft
Sebaceous gland
4
Sagittal section through the
upper eyelid.
A hair follicle with associated structures.
References
[1] http:/ / education. yahoo. com/ reference/ gray/ subjects/ subject?id=234#p1069
[2] http:/ / www. nlm. nih. gov/ cgi/ mesh/ 2007/ MB_cgi?mode=& term=Sebaceous+ glands
[3] Dellmann's textbook of veterinary histology (405 pages), Jo Ann Coers Eurell, Brian L. Frappier, 2006, p.29, weblink: Books-Google-RTOC
(http:/ / books. google. com/ books?id=FnS4uiOlRT0C& pg=PA29& lpg=PA29).
[4] 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.
[5] "Exercise 15: Hair", VT.edu, 2008, webpage: Vetmed-lab15 (http:/ / education. vetmed. vt. edu/ Curriculum/ VM8054/ Labs/ Lab15/ Lab15.
htm).
[6] "Hair Care: An Illustrated Dermatologic Handbook", Zoe Diana Draelos, Zoe Kececioglu Draelos, 2005, p.26, web: Books-Google-5QC
(http:/ / books. google. com/ books?id=Z2rHHGQc-5QC& pg=PA26& lpg=PA26): oily hair & detergents.
[7] Downing DT, Stewart ME, Wertz PW, Colton SW, Abraham W, Strauss JS (March 1987). "Skin lipids: an update". The Journal of
Investigative Dermatology 88 (3 Suppl): 2s–6s. doi:10.1111/1523-1747.ep12468850. PMID 2950180.
[8] Cheng JB, Russell DW (September 2004). "Mammalian wax biosynthesis. II. Expression cloning of wax synthase cDNAs encoding a
member of the acyltransferase enzyme family" (http:/ / www4. utsouthwestern. edu/ moleculargenetics/ pdf/ dr_cur_res/ JBiolChem2004-II.
pdf). The Journal of Biological Chemistry 279 (36): 37798–807. doi:10.1074/jbc.M406226200. PMID 15220349. PMC 2743083. .
[9] 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.
[10] http:/ / www. summitplc. com/ uploads/ RNSSeborrhoeatrialFINAL. pdf
[11] 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.
[12] Playe, Stephen J (July 2002). "Infectious Complications of Body Art: Infection is reported in about 1% of tattoos and in up to 45% of
piercings, depending on the technique employed, body location, and after care" (http:/ / journals. lww. com/ em-news/ Citation/ 2002/ 07000/
Infectious_Complications_of_Body_Art__Infection_is. 7. aspx). Emergency Medicine News 24 (7): 10–3.
doi:10.1097/01.EEM.0000334232.52899.06 (inactive 2010-06-14). .
Sebaceous gland
External links
• Histology at BU 08801loa (http://www.bu.edu/histology/p/08801loa.htm) - "Integument: scalp"
• MeSH Sebaceous+Glands (http://www.nlm.nih.gov/cgi/mesh/2009/MB_cgi?mode=&term=Sebaceous+
Glands)
5
Article Sources and Contributors
Article Sources and Contributors
Sebaceous gland Source: http://en.wikipedia.org/w/index.php?oldid=395368752 Contributors: 1st2Bomb, AED, Abdull, Aitias, Andycjp, AnnaP, Arcadian, Auntof6, AxelBoldt, Bansp,
Bobo192, CerealBabyMilk, Ceyockey, Chris Capoccia, CommonsDelinker, CrazyInSane, Darklilac, Davewho2, DeadEyeArrow, Divide, Dougluce, Dprady, Dr. Doof, Dreamer.redeemer, Ds13,
Edgar181, Evets21, Fences and windows, Fsotrain09, Fuzzbox, Fuzzy901, Geni, Hankwang, Helix84, Hightower 40, Intersofia, Iraqidude, Jchae88, Kajerm, Kjkolb, Lando242, Lichee66,
Majorly, MarcoTolo, Mattygabe, Mctt, Mikael Häggström, Mikekearn, Moshe Constantine Hassan Al-Silverburg, My Core Competency is Competency, Neckoneckonecko, Neilbeach, Nuno
Tavares, Oatmeal batman, Obli, OlEnglish, Pablo X, Peter Ellis, Ph.eyes, Pwjb, R sirahata, RDBrown, Rlfb, Rogermw, Rune X2, Saleen1996, Seanmiz, Smulthaup, SofiaSoGood, Sprostini,
Steven Walling, Stratuspower88, TLazzo, Taco325i, That Guy, From That Show!, Tjmayerinsf, UnicornTapestry, Vojtech.dostal, Vsion, WLU, Waitak, Wikid77, Wikijens, Wolfkeeper,
Writerite, X-Fi6, Yvwv, Zinnmann, 102 anonymous edits
Image Sources, Licenses and Contributors
Image:HairFollicle.png Source: http://en.wikipedia.org/w/index.php?title=File:HairFollicle.png License: unknown Contributors: User:Helix84
Image:Skin.jpg Source: http://en.wikipedia.org/w/index.php?title=File:Skin.jpg License: Public Domain Contributors: US-Gov
Image:Haarbalgmilbe.jpg Source: http://en.wikipedia.org/w/index.php?title=File:Haarbalgmilbe.jpg License: Creative Commons Attribution-Sharealike 2.5 Contributors: Blauerauerhahn,
Eusebius
Image:Pilosebaceous_Unit_4x.JPG Source: http://en.wikipedia.org/w/index.php?title=File:Pilosebaceous_Unit_4x.JPG License: unknown Contributors: User:Kilbad
Image:Base of Pilosebaceous Unit 10x.JPG Source: http://en.wikipedia.org/w/index.php?title=File:Base_of_Pilosebaceous_Unit_10x.JPG License: Public Domain Contributors: Kilbad
Image:Insertion_of_sebaceous_glands_into_hair_shaft_x10.jpg Source: http://en.wikipedia.org/w/index.php?title=File:Insertion_of_sebaceous_glands_into_hair_shaft_x10.jpg License:
Public Domain Contributors: User:Kilbad
Image:Gray893.png Source: http://en.wikipedia.org/w/index.php?title=File:Gray893.png License: Public Domain Contributors: Arcadian, 1 anonymous edits
Image:Gray944.png Source: http://en.wikipedia.org/w/index.php?title=File:Gray944.png License: unknown Contributors: Keenan Pepper, Lennert B, Man vyi, Omegatron
License
Creative Commons Attribution-Share Alike 3.0 Unported
http:/ / creativecommons. org/ licenses/ by-sa/ 3. 0/
6