Gland
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Gland | |
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![]() Humansubmandibular gland.At the right is a group of mucousacini,at the left a group of serous acini. | |
Details | |
Identifiers | |
Latin | glandula |
TH | H2.00.02.0.02002 |
Anatomical terminology |
Aglandis acellor anorganin an animal's body that produces and secretes different substances either into the bloodstream or into a body cavity or outer surface that the organism needs.[1]A gland may also function to remove unwanted substances such asurinefrom the body.[2]
There are two types of gland each with a different method of secretion.Endocrine glandsare ductless and secrete their products,hormones,directly into interstitial spaces to be taken up into the bloodstream.Exocrine glandssecrete their products through a duct into a body cavity or outer surface.[2]
Glands are mostly composed ofepithelial tissue,and typically have a supporting framework of connective tissue, and a capsule.[2]
Structure
[edit]Development
[edit]![](https://upload.wikimedia.org/wikipedia/commons/thumb/5/52/Types_Arrangements_of_Glands_1.png/220px-Types_Arrangements_of_Glands_1.png)
![](https://upload.wikimedia.org/wikipedia/commons/thumb/a/a8/Types_Arrangements_of_Glands_2.png/220px-Types_Arrangements_of_Glands_2.png)
Every gland is formed by an ingrowth from anepithelialsurface. 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.[3]
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.[3]
Glands are classified according to their shape.
- If the gland retains its shape as a tube throughout it is termed atubular gland.
- In the second main variety of gland the secretory portion is enlarged and thelumensvariously increased in size. These are termedalveolaror saccular glands.[3]
Types of glands
[edit]Glands are divided based on their function into two groups:
![](https://upload.wikimedia.org/wikipedia/commons/thumb/f/fc/Endocrine_vs._Exocrine.svg/220px-Endocrine_vs._Exocrine.svg.png)
Endocrine glands
[edit]Endocrine glandssecrete substances that circulate through the bloodstream. The glands secrete their products throughbasal laminainto 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 secretehormoneswhich play an important role in maintaininghomeostasis.Thepineal gland,thymus gland,pituitary gland,thyroid gland,and the twoadrenal glandsare all endocrine glands.
Exocrine glands
[edit]Exocrine glandssecrete their products through aductonto an outer or inner surface of the body, such as the skin or thegastrointestinal tract.Secretion is directly onto theapicalsurface. The glands in this group can be divided into three groups:
- Merocrineglands – cells secrete their substances byexocytosis.(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)
- Apocrineglands – a portion of the secretingcell's body is lost during secretion. The termApocrine glandis often used to refer to theapocrine sweat glands,however it is thought that apocrinesweat glandsmay 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)
- Holocrineglands – the entire cell disintegrates to secrete its substances. (e.g.sebaceous glands:meibomianandzeis glands)
Exocrine glands can further be categorized by their product:
- Serousglands secrete a watery, often protein-rich, fluid-like product, e.g. sweat glands.
- Mucousglands secrete a viscous product, rich incarbohydrates(such as glycoproteins), e.g.goblet cells.
- Sebaceousglands secrete alipidproduct. These glands are also known as oil glands, e.g.Fordyce spotsandmeibomian glands.
Clinical significance
[edit]![](https://upload.wikimedia.org/wikipedia/commons/thumb/0/05/Histopathology_of_sclerosing_adenosis_of_the_breast.jpg/220px-Histopathology_of_sclerosing_adenosis_of_the_breast.jpg)
![]() | This sectionneeds expansion.You can help byadding to it.(April 2014) |
Adenosisis anydiseaseof a gland. The diseased gland has abnormal formation or development ofglandular tissuewhich is sometimestumorous.[4]
References
[edit]- ^"Definition of Gland".medicinenet.com.Archived fromthe originalon 14 December 2017.Retrieved2 May2018.
- ^abcSaladin, Kenneth S. (2011).Human anatomy(3rd ed.). New York: McGraw-Hill. pp. 73–75.ISBN9780071222075.
- ^abcpublic domain:Chisholm, Hugh,ed. (1911). "Epithelial, Endothelial and Glandular Tissues".Encyclopædia Britannica.Vol. 9 (11th ed.). Cambridge University Press. pp. 705–707. One or more of the preceding sentences incorporates text from a publication now in the
- ^Alberts, Daniel (2012).Dorland's illustrated medical dictionary(32nd ed.). Philadelphia, PA: Saunders/Elsevier. p. 30.ISBN978-1-4160-6257-8.
External links
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