The sebaceous glands are glands found in the skin of mammals.
| Sebaceous gland | |
|---|---|
 Schematic view of a hair follicle with sebaceous gland. | |
 Cross-section of all skin layers.A hair follicle with associated structures. (Sebaceous gland 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 | |
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 |
Locations of glands
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 reaches the surface through ducts. 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.
Changes in life cycle
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
-
Sagittal section through the upper eyelid. -
A hair follicle with associated structures.
References
- ^ 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
- ^ Abuse Of Anabolic Steroids Causes Acne In Bodybuilders, by Medinda.com
External links
- Histology image: 08801loa – Histology Learning System at Boston University - "Integument: scalp"