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sebaceous gland

Did you mean: sebaceous gland (in anatomy), sebaceous

 
Dictionary: sebaceous gland

n.

Any of various glands in the dermis of the skin that open into a hair follicle and produce and secrete sebum.


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Sci-Tech Encyclopedia: Sebaceous gland
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A gland which produces and liberates sebum, a mixture composed of fat, cellular debris, and keratin. When the gland arises in association with a hair follicle, it forms a thickened outpushing from the side of the developing follicle near the epidermis. Central cells in these sebaceous glands form oil droplets within the cytoplasm. These cells disintegrate to liberate the sebaceous substance and are therefore of the holocrine type. The Meibomian or tarsal glands, within the tarsus or supporting plate at the edge of the eyelids, are sebaceous and complex tubuloacinous structures. The numerous separate glands open along the entire edge of the upper and lower lids. Retained secretions of the tarsal glands produce a chalozion or Meibomian cyst. See also Gland.


Dental Dictionary: sebaceous glands
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(sēbā′shəs)
n.pl

Exocrine glands of the skin, many of which open into the hair follicles and secrete an oily substance that coats the hair and surrounding epithelium, helping to prevent evaporation of sweat and retain body heat. In the oral cavity, these glands are known as Fordyce’s granules or Fordyce’s spots and can be seen with the unaided eye as yellowish-white in color and are more common in older adults on the buccal and labial mucosa.

Britannica Concise Encyclopedia: sebaceous gland
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Small oil-producing gland in the skin, usually connected to a hair follicle by a duct into which it releases sebum, a component of the slightly greasy film on the skin that helps keep it flexible and prevents too much water loss or absorption. The glands are distributed over the entire body except the palms and soles, most abundantly on the scalp and face. Large and well developed at birth, they shrink during childhood but enlarge again and increase their sebum output at puberty (apparently in response to male hormones), often leading to acne.

For more information on sebaceous gland, visit Britannica.com.

 
Columbia Encyclopedia: sebaceous gland
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sebaceous gland (səbā'shəs), gland in the skin of mammals that secretes an oily substance called sebum. In humans, sebaceous glands are primarily found in association with hair follicles but also occur in hairless areas of the skin, except for the palms of the hand and soles of the feet. Sebum is a mixture of fat and the debris of dead fat-producing cells. These cells are constantly replaced by new growth at the base of the glands. Generally the sebum is deposited on the hairs inside the follicles and is brought up to the surface of the skin along the hair shaft. In hairless areas, the sebum surfaces through ducts. Sebum lubricates and protects the hair and skin and prevents drying and irritation of membranes. Sebum may collect excessively as a result of poor hygiene, a diet rich in fats, or accelerated glandular activity, especially during adolescence. Excessive secretions of sebum may be related to acne, certain forms of baldness, and other skin disorders.


Health Dictionary: sebaceous glands
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(si-bay-shuhs)

Glands located in the skin that secrete an oily substance, sebum. Sebum lubricates the skin and hair.

  • Clogged sebaceous glands can result in pimples.

  • Wikipedia: Sebaceous gland
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    Sebaceous gland
    HairFollicle.png
    Schematic view of hair follicle & sebaceous gland.
    Skin.jpg
    Cross-section of all skin layers. A hair follicle with associated structures. (Sebaceous gland labeled at center left.)
    Latin glandula sebacea
    Gray's subject #234 1069
    MeSH Sebaceous+glands

    The sebaceous glands are microscopic glands in the skin which secrete an oily/waxy matter, called sebum, to lubricate the skin and hair of animals.[1] 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.[2] In the eyelids, meibomian sebaceous glands secrete sebum into tears. There are several related medical conditions, including: acne, sebaceous cysts, hyperplasia, sebaceous adenoma and sebaceous gland carcinoma (see section below: Pathology).

    Contents

    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 sebum into the tears coating the eye, to slow evaporation.

    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.[3] 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,[4] as in hot weather or if not washed for several days. Earwax is partly composed of sebum. Excessive sebum can be cleansed with detergent (as found in shampoo for oily hair), rather than just using bath soap.[4] Sebum secretion might increase after the first cleansing, so a secondary wash might be needed sooner (such as within half a day). Also, sebum will remain at lower temperatures, when rinsing hair with cold water, so showers should rinse in warm water (as between 37-38ºC, 98-100ºF).[5] Excess sebum has been linked to eating red meats, fried, oily or other foods, but studies are not conclusive.

    Function

    Sebum acts to protect and waterproof hair and skin,[6] and keeps them from becoming dry, brittle and cracked by dehydration. It can also inhibit the growth of some microorganisms (such as some bacteria) on the skin.[6]

    Composition

    The composition of sebum varies from species to species; in humans, the lipid content is as follows:[7]

    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.

    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 during and after puberty. This is however normal, not to be confused with an STD. In females, they appear predominantly in the labia minora.

    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 and repartitioning effects, tends to stimulate the sebaceous glands, which can cause acne.[8]

    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.[9]

    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.

    Additional images

    References

    1. ^ Dellmann's textbook of veterinary histology (405 pages), Jo Ann Coers Eurell, Brian L. Frappier, 2006, p.29, weblink: Books-Google-RTOC.
    2. ^ James, William; Berger, Timothy; Elston, Dirk (2005) Andrews' Diseases of the Skin: Clinical Dermatology (10th ed.). Saunders. Page 7. ISBN 0721629210.
    3. ^ "Exercise 15: Hair", VT.edu, 2008, webpage: Vetmed-lab15.
    4. ^ a b "Hair Care: An Illustrated Dermatologic Handbook", Zoe Diana Draelos, Zoe Kececioglu Draelos, 2005, p.26, web: Books-Google-5QC: oily hair & detergents.
    5. ^ "Beijing 101 Hair Consultants - Q&A", Beijing101Hair.com, 2009, web: B101-qna: Rinsing hair "with cold water after that will cause the sebum to stay on the scalp. Hence, set water temperature for your shower between 37ºC to 38ºC."
    6. ^ a b "Natural Skin Care for Oily Skin - Wellsphere", Wellsphere.com, 2009, webpage: WS-skin-sebum.
    7. ^ Jeffrey B. Cheng and David W. Russell. Mammalian Wax Biosynthesis II: Expression Cloning of Wax Synthase cDNAs Encoding a Member of the Acyltransferase Enzyme Family, J Biol Chem. 2004 Sep 3;279(36):37798-37807. PMID 15220349 Fulltext
    8. ^ Abuse Of Anabolic Steroids Causes Acne In Bodybuilders, by Medinda.com
    9. ^ 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". Emergency Medicine News 24 (7): 10–13. doi:10.1097/01.EEM.0000334232.52899.06. ISSN 1552-3624. http://www.em-news.com/pt/re/emmednews/abstract.00132981-200207000-00007.htm;jsessionid=J3QHjVQl5vQqyyYhpdNxppJvvBPpkX7jNgj7f6HKFwsk6JhqCtp9!928310026!181195629!8091!-1. 

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    Did you mean: sebaceous gland (in anatomy), sebaceous


     

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    Dictionary. The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.  Read more
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    Dental Dictionary. Mosby's Dental Dictionary. Copyright © 2004 by Elsevier, Inc. All rights reserved.  Read more
    Britannica Concise Encyclopedia. Britannica Concise Encyclopedia. © 2006 Encyclopædia Britannica, Inc. All rights reserved.  Read more
    Columbia Encyclopedia. The Columbia Electronic Encyclopedia, Sixth Edition Copyright © 2003, Columbia University Press. Licensed from Columbia University Press. All rights reserved. www.cc.columbia.edu/cu/cup/ Read more
    Health Dictionary. The New Dictionary of Cultural Literacy, Third Edition Edited by E.D. Hirsch, Jr., Joseph F. Kett, and James Trefil. Copyright © 2002 by Houghton Mifflin Company. Published by Houghton Mifflin. All rights reserved.  Read more
    Wikipedia. This article is licensed under the Creative Commons Attribution/Share-Alike License. It uses material from the Wikipedia article "Sebaceous gland" Read more