SEBACEOUS GLAND

The 'sebaceous glands' are glands found in the skin of mammals.

Contents

Locations and morphology

Sebum

Function

Composition

Changes during development

Pathology

Importance to other animals

Additional images

References

External links

Locations and morphology

A branched type of acinar gland, these 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 to deposit sebum on the hairs, and bring it to the skin surface along the hair shaft. The structure consisting of hair, hair follicle and sebaceous gland is known as 'pilosebaceous unit'.
Sebaceous glands are also found in non-haired areas of eyelids, 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 that secrete sebum into the tears coating the eye to prevent evaporation.

Sebum

Sebaceous glands secrete an oily 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 holocrine glands.
Sebum is odorless, but its bacterial breakdown can produce odors. Sebum is the cause of some people experiencing "oily" hair if it is not washed for several days. Earwax is partly composed of sebum.

Function

Sebum acts to protect and waterproof hair and skin, and keep them from becoming dry, brittle and cracked. It can also inhibit the growth of microorganisms on skin.

Composition

The composition of sebum varies from species to species; in humans, the lipid content is as follows:^[1]

'Percent composition'	'Substance'
25%	wax monoesters
41%	triglycerides
16%	free fatty acids
12%	squalene

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. 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 tend to stimulate the sebaceous glands which can cause acne.^[2]
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.

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. 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
2. Abuse Of Anabolic Steroids Causes Acne In Bodybuilders, by Medinda.com

External links

★ - "Integument: scalp"