Gland
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).
Glands can be devided 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.
**
Merocrine glands - cells secrete their substances by
exocytosis.Typical exocrine glands include sweat glands, salivary glands, mammary glands and many glands of the digestive system.
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, simple tubular if there is no division (
large intestine), compound tubular if branching occurs (
pyloric glands of stomach). In the simple tubular glands the gland may be coiled without losing its tubular form, e.g. in
sweat glands.
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. They are again subdivided into simple or compound alveolar glands, as in the case of the tubular glands. A further complication in the case of the alveolar glands may occur in the form of still smaller saccular diverticuli growing out from the main sacculi. These are termed
alveoli.
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.
