Everything about The Sebaceous Gland totally explained
The
sebaceous glands are
glands found in the
skin of
mammals.
Locations and morphology
A branched type of
acinar gland, these glands exist in humans throughout the skin except in the
palms of the hands, lips and
soles of the feet.
Sebaceous glands can usually be found in hair-covered areas, where they're connected to
hair follicles. 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,
penis,
labia minora, and
nipples. Here, the sebum traverses ducts which terminate in
sweat pores on the surface of the skin. The inner surface of the lip contains sebaceous glands also, here they're common as
Fordyce's spots.
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 an oily substance called
sebum (
Latin, meaning
fat or
tallow) that's 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 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 several days.
Earwax is partly composed of sebum.
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:
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 normal, however, and 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.
A blocked sebaceous gland can result in a
sebaceous cyst.
One condition involving enlarged sebaceous glands is known as
sebaceous hyperplasia. Another common condition is
seborrheic dermatitis.
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
Image:Gray893.png|Sagittal section through the upper eyelid.
Image:Gray944.png|A hair follicle with associated structures.
Further Information
Get more info on 'Sebaceous Gland'.
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