Gland
From Wikipedia, the free encyclopedia
- For other uses, see Gland (disambiguation).
A gland is an organ in an animal's body that synthesizes a substance for release such as hormones, often into the bloodstream (endocrine gland) or into cavities inside the body or its outer surface (exocrine gland).
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[edit] Types of gland
Glands can be divided into two groups:
- Endocrine glands- are glands that secrete their product directly onto a surface rather than through a duct.
- Exocrine glands- secrete their products via a duct, the glands in this group can be divided into three groups:
- Apocrine glands - a portion of the secreting cell's body is lost during secretion. Apocrine gland is often used to refer to the apocrine sweat glands.
- Holocrine glands - the entire cell disintegrates to secrete its substances (e.g., sebaceous glands)
- Merocrine glands - cells secrete their substances by exocytosis (e.g., mucous and serous glands). Also called "eccrine."
The type of secretory product of an Exocrine gland may also be one of three categories:
- Serous glands- secrete a watery, often protein-rich product
- Mucous glands- secrete a viscous product, rich in carbohydrates (e.g., glycoproteins)
- Sebaceous glands- secrete a lipid product
[edit] Formation
Every gland is formed by an ingrowth from an epithelial surface. This ingrowth may from the beginning possess a tubular structure, but in other instances glands may start as a solid column of cells which subsequently becomes tubulated.
As growth proceeds, the column of cells may divide or give off offshoots, in which case a compound gland is formed. In many glands the number of branches is limited, in others (salivary, pancreas) a very large structure is finally formed by repeated growth and sub-division. As a rule, the branches do not unite with one another, but in one instance, the liver, this does occur when a reticulated compound gland is produced. In compound glands the more typical or secretory epithelium is found forming the terminal portion of each branch, and the uniting portions form ducts and are lined with a less modified type of epithelial cell.
Glands are classified according to their shape.
- If the gland retains its shape as a tube throughout it is termed a tubular gland.
- In the second main variety of gland the secretory portion is enlarged and the lumen variously increased in size. These are termed alveolar or saccular glands.
[edit] Naming
Glands typically may be referred to by two or more means, though some terms are rarely seen. The names of the anatomists who first described them are often employed, as:
- Bartholin's glands - Tiedmann's glands. The vulvovaginal glands.
- Baughin's glands - nonserous or mixed glands near the tip of the tongue. The anterior lingual glands.
- Boerhaave's glands - the sudoriparous glands.
- Bowman's glands - glands in the olfactory region of the nose.
- Ciaccio's glands - the accessory lacrimal glands.
- Cobelli's glands - mucous glands in the mucosa of the esophagus just above the cardia.
- Cowper's glands - bulbourethral glands. Also called Mery's glands.
- Duverney's gland - a minute gland on either side of the vagina.
- Ebner's glands - mucous glands of the tongue.
- Fränkel's glands - minute glands that open below the edge of the vocal cords.
- Gley's glands - the parathyroid glands. Also called Sandstroem's glands.
- Guérin's glands - Skene's glands.
- Henle's glands - tubular glands in the conjuctiva of the eyelids.
- Huguier's glands - two minor vaginal glands.
- Krause's glands - mucous glands of the middle portion of the conjunctiva.
- Lieberkuhn's glands - simple tubular glands opening on the surface of the intestinal mucous membrane.
- Littré's glands - racemose glands in the spongy portion of the urethra. Also called Morgagni's glands.
- Luschka's gland or ganglion - coccygeal gland or glomus coccygeum, a small vascular organ near the tip of the coccyx.
- Moll's glands - certain small glands of the eyelids.
- Montgomery's glands - sebaceous glands of the mammary areola.
- Naboth's glands - distended mucous glands within the cervix and about the os uteri.
- Peyer's glands - lymphatic glands, chiefly of the ileum.
- Rivini's gland - the sublingual gland.
- Sigmund's glands - the epitrochlear lymph nodes.
- Suzanne's gland - a mucous gland of the mouth, beneath the alveolingual groove.
- Wasmann's glands - the peptic glands.
- Weber's glands - the tubular mucous glands of the tongue.
- Glands of Zeis - sebaceous glands on the free edges of the eyelids. Named for Edward Zeis (1807-68), ophthalmologist at Dresden.
[edit] References
- This article incorporates text from the Encyclopædia Britannica Eleventh Edition, a publication now in the public domain.ar:غدة
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