View source for Gland

{{short description|Type of animal organ}}
{{About|the gland in animals|information specific to plants|Gland (botany)}}
{{other uses}}{{Additional citations|date=April 2024}}{{Infobox anatomy
| Name        = Gland
| Latin       = glandula
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| Caption     = Human [[submandibular gland]]. At the right is a group of mucous [[acinus|acini]], at the left a group of serous acini.
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A '''gland''' is a [[Cell (biology)|cell]] or an [[Organ (biology)|organ]] in an animal's body that produces and secretes different substances that the organism needs, either into the bloodstream or into a body cavity or outer surface.<ref>{{cite web|url=https://www.medicinenet.com/script/main/art.asp?articlekey=3594|title=Definition of Gland|website=medicinenet.com|access-date=2 May 2018|url-status=dead|archive-url=https://web.archive.org/web/20171214182347/https://www.medicinenet.com/script/main/art.asp?articlekey=3594|archive-date=14 December 2017}}</ref> A gland may also function to remove unwanted substances such as [[urine]] from the body.<ref name="Saladin1">{{cite book |last1=Saladin |first1=Kenneth S. |title=Human anatomy |date=2011 |publisher=McGraw-Hill |location=New York |isbn=9780071222075 |pages=73–75 |edition=3rd}}</ref>

There are two types of gland, each with a different method of secretion. [[Endocrine gland]]s are ductless and secrete their products, [[hormone]]s,  directly into interstitial spaces to be taken up into the bloodstream. [[Exocrine gland]]s secrete their products through a duct into a body cavity or outer surface.<ref name="Saladin1" />

Glands are mostly composed of [[epithelium|epithelial tissue]], and typically have a supporting framework of connective tissue, and a capsule.<ref name="Saladin1" />

==Structure==
{{See also|List of glands of the human body}}

===Development===
[[File:Types Arrangements of Glands 1.png|thumb|This image shows some of the various possible glandular arrangements. These are the simple tubular, simple branched tubular, simple coiled tubular, simple acinar, and simple branched acinar glands.]]
[[File:Types Arrangements of Glands 2.png|thumb|This image shows some of the various possible glandular arrangements. These are the compound tubular, compound acinar, and compound tubulo-acinar glands.]]
Every gland is formed by an ingrowth from an [[epithelium|epithelial]] surface. This ingrowth may in the beginning possess a tubular structure, but in other instances glands may start as a solid column of cells which subsequently becomes tubulated.<ref name=EB1911>{{EB1911 |wstitle=Epithelial, Endothelial and Glandular Tissues |volume=9 |pages=705–707 |inline=1}}</ref>

As growth proceeds, the column of cells may split 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. One exception to this rule is the [[liver]]; this occurs 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.<ref name=EB1911/>

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 (anatomy)|lumens]] variously increased in size. These are termed [[alveolar gland|alveolar]] or saccular glands.<ref name=EB1911/>

==Types of glands==
Glands are divided based on their function into two groups:

[[File:Endocrine vs. Exocrine.svg|thumb|This diagram shows the differences between endocrine and exocrine glands. The major difference is that exocrine glands secrete substances out of the body and endocrine glands secrete substances into capillaries and blood vessels.]]

===Endocrine glands===
{{Main|Endocrine gland}}
[[Endocrine gland]]s secrete substances that circulate through the bloodstream. The glands secrete their products through [[basal lamina]] into the bloodstream. Basal lamina typically can be seen as a layer around the glands to which more than a million tiny blood vessels are attached. These glands often secrete [[hormone]]s which play an important role in maintaining [[homeostasis]]. The [[pineal gland]], [[thymus gland]], [[pituitary gland]], [[thyroid gland]], and the two [[adrenal gland]]s are all endocrine glands.

===Exocrine glands=== 
{{Main|Exocrine gland}}
[[Exocrine gland]]s secrete their products through a [[Duct (anatomy)|duct]] onto an outer or inner surface of the body, such as the skin or the [[human gastrointestinal tract|gastrointestinal tract]]. Secretion is directly onto the [[apical membrane|apical]] surface. The glands in this group can be divided into three groups:
* [[Merocrine]] glands – cells secrete their substances by [[exocytosis]]. (e.g. mucous and serous glands; also called "[[eccrine]]", e.g. major sweat glands of humans, goblet cells, salivary gland, tear gland and intestinal glands)
* [[Apocrine]] glands – a portion of the secreting [[cell (biology)|cell]]'s body is lost during secretion. The term ''Apocrine gland'' is often used to refer to the [[sweating|apocrine sweat glands]], however it is thought that apocrine [[sweat gland]]s may not be true apocrine glands as they may not use the apocrine method of secretion. (e.g. mammary gland, sweat gland of arm pit, pubic region, skin around anus, lips and nipples)
* [[Holocrine]] glands – the entire cell disintegrates to secrete its substances. (e.g. [[sebaceous gland]]s: [[meibomian gland|meibomian]] and [[Gland of Zeis|zeis gland]]s)

Exocrine glands can further be categorized by their product:
* [[Serous]] glands secrete a watery, often protein-rich, fluid-like product, e.g. sweat glands.
* [[mucus|Mucous]] glands secrete a viscous product, rich in [[carbohydrates]] (such as glycoproteins), e.g. [[goblet cell]]s.
* [[Sebaceous]] glands secrete a [[lipid]] product. These glands are also known as oil glands, e.g. [[Fordyce spots]] and [[meibomian gland]]s.

==Clinical significance==
[[File:Histopathology of sclerosing adenosis of the breast.jpg|thumb|Histopathology of sclerosing adenosis of the breast.]]
{{Expand section|date=April 2014}}
'''Adenosis''' is any [[disease]] of a gland. The diseased gland has abnormal formation or development of [[Epithelium#Glandular tissue|glandular tissue]] which is sometimes [[neoplasm|tumorous]].<ref>{{cite book|last1=Alberts|first1=Daniel|title=Dorland's illustrated medical dictionary.|date=2012|publisher=Saunders/Elsevier|location=Philadelphia, PA|isbn=978-1-4160-6257-8|page=30|edition=32nd}}</ref>

==References==
{{Reflist}}

== External links ==
* {{Commons-inline}}
* {{Wiktionary-inline|gland}}

{{Epithelium and epithelial tissue}}
{{Authority control}}

[[Category:Glands| ]]