- Sebaceous gland
Name = Sebaceous gland
Latin = glandula sebacea
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Caption = Schematic view of a hair follicle with sebaceous gland.
Caption2 = Cross-section of all skin layers. A hair follicle with associated structures. (Sebaceous gland labeled at center left).
MeshName = Sebaceous+glands
MeshNumber = A10.336.827
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The sebaceous glands are
glands found in the skinof mammals.
Locations and morphology
A branched type of
acinar gland, these glands exist in humans throughout the skin except in the palms of the handsand soles of the feet.
Sebaceous glands can usually be found in hair-covered areas, where they are connected to
hair follicles. The glands deposit sebumon 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, penis, labia minora, and nipples. Here, the sebum traverses ducts which terminate in sweat pores on the surface of the skin. Pores range in size from 50 to 80 μm on average [http://answers.google.com/answers/threadview?id=548539] .
The inner surface of the lip and the
buccalsurface of the cheek can potentially contain ectopic sebaceous glands commonly known as Fordyce's spotsor Fordyce granules. These occur as yellowish circular dots that form clusters. Eighty percent of the population have Fordyce granules and these sebaceous glands are asymptomatic.
At the rim of the eyelids,
meibomian glands are a specialized form of sebaceous gland. They secrete sebum into the tearscoating the eye, to slow evaporation.
Sebaceous glands secrete a waxy substance called sebum (
Latin, meaning " fat" or " tallow") that is made of fat ( lipids) and the debris of dead fat-producing cells. In the glands, sebum is produced within specialized cells and is released as these cells burst; sebaceous glands are thus classified as holocrineglands.Sebum itself is odorless, but its bacterial breakdown can produce odors. Sebum is one cause of some people experiencing "oily" hair or skin if not washed for some time. Earwaxis partly composed of sebum.
Sebum acts to protect and waterproof
hairand skin, and keep them from becoming dry, brittle, and cracked.Fact|date=September 2008 It can also inhibit the growth of microorganisms on skin.Fact|date=September 2008
The composition of sebum varies from species to species; in humans, the lipid content is as follows: [cite journal |author=Cheng JB, Russell DW |title=Mammalian wax biosynthesis. II. Expression cloning of wax synthase cDNAs encoding a member of the acyltransferase enzyme family |journal=J. Biol. Chem. |volume=279 |issue=36 |pages=37798–807 |year=2004 |pmid=15220349 |doi=10.1074/jbc.M406226200 |url=http://www4.utsouthwestern.edu/moleculargenetics/pdf/dr_cur_res/JBiolChem2004-II.pdf]
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
pubertybecause of heightened levels of androgens. In males, sebaceous glands begin to appear predominantly on the penisduring and after puberty. This is normal, however, and not to be confused with an STD.In females, they appear predominantly in the labia minora.
Sebaceous glands are involved in skin problems such as acne and
keratosis pilaris. The prescription drug isotretinoinsignificantly 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 and repartitioning effects tend to stimulate the sebaceous glands which can cause acne. [ [http://www.steroid.com/sitenews/?EC=ReadArticle&ArticleID=5 Abuse Of Anabolic Steroids Causes Acne In Bodybuilders] , by Medinda.com]
A blocked sebaceous gland can result in a
One condition involving enlarged sebaceous glands is known as
sebaceous hyperplasia. Another common condition is seborrheic dermatitis. Sebaceous gland carcinomais a rare and aggressive form of cancerinvolving the sebaceous glands; sebaceous adenomais a more benign neoplasmof the sebaceous glands.
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.
preputial glands of mice and rats are large modified sebaceous glands that produce pheromones.
* - "Integument: scalp"
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