Editing Connective tissue

{{Short description|Type of biological tissue in animals}}
{{Infobox anatomy
| Name        = Connective tissue
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| Caption     = Section of [[epididymis]]. Connective tissue (blue) is seen supporting the [[epithelium]] (purple).
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'''Connective tissue''' is one of the four primary types of [[tissue (biology)#Animal tissue|animal tissue]], a group of cells that are similar in structure, along with [[epithelial tissue]], [[muscle tissue]], and [[nervous tissue]].<ref name="oregon">{{Cite web |last=Biga |first=Lindsay M. |last2=Dawson |first2=Sierra |last3=Harwell |first3=Amy |date=26 September 2019 |title=4.1 Types of Tissues |url=https://open.oregonstate.education/aandp/chapter/4-1-types-of-tissues/ |access-date=30 July 2022 |language=en}}</ref> It develops mostly from the [[mesenchyme]], derived from the [[mesoderm]], the middle [[embryo]]nic [[germ layer]].<ref name="Biga" /> Connective tissue is found in between other tissues everywhere in the body, including the [[nervous system]]. The three [[meninges]], membranes that envelop the [[brain]] and [[spinal cord]], are composed of connective tissue. Most types of connective tissue consists of three main components: [[elastic fiber|elastic]] and [[collagen fibers]], [[ground substance]], and [[cell (biology)|cells]].<ref name="Biga" /> [[Blood]] and [[lymph]] are classed as specialized fluid connective tissues that do not contain fiber.<ref name="Biga" /><ref name="libre">{{Cite web |date=21 May 2021 |title=5.3.4: Fluid Tissues |url=https://bio.libretexts.org/Courses/West_Hills_College_-_Lemoore/Human_Anatomy_Laboratory_Manual_(Hartline)/05%3A_Tissues/5.03%3A_Connective_Tissues/5.3.04%3A_Fluid_Tissues |access-date=2 August 2022 |website=Biology LibreTexts |language=en}}</ref> All are immersed in the [[body water]]. The cells of connective tissue include [[fibroblast]]s, [[adipocyte]]s, [[macrophage]]s, [[mast cell]]s and [[leukocyte]]s.

The term "connective tissue" (in German, {{Lang|de|Bindegewebe}}) was introduced in 1830 by [[Johannes Peter Müller]]. The tissue was already recognized as a distinct class in the 18th century.<ref>Mathews, M. B. (1975). ''Connective Tissue, Macromolecular Structure Evolution.'' Springer-Verlag, Berlin and New York. [https://books.google.com/books?id=_xf2CAAAQBAJ link].</ref><ref>{{Cite journal |last=Aterman |first=K. |year=1981 |title=Connective tissue: An eclectic historical review with particular reference to the liver |journal=The Histochemical Journal |volume=13 |issue=3 |pages=341–396 |doi=10.1007/BF01005055 |pmid=7019165 |s2cid=22765625}}</ref>

==Types==
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Connective tissue can be broadly classified into connective tissue proper, and special connective tissue.<ref>{{Cite web |last=Shostak |first=Stanley |title=Connective Tissues |url=http://www.pitt.edu/~sshostak/biosci1450/hislec03.html |access-date=9 December 2012}}</ref><ref name="PorthMatfin2010">{{Cite book |last=Carol Mattson Porth |url=https://books.google.com/books?id=FFg88IaReBwC&pg=PA24 |title=Essentials of Pathophysiology: Concepts of Altered Health States |last2=Glenn Matfin |date=1 October 2010 |publisher=Lippincott Williams & Wilkins |isbn=978-1582557243 |pages=24– |access-date=11 May 2011}}</ref> Connective tissue proper includes loose connective tissue, and dense connective tissue. Loose and dense connective tissue are distinguished by the ratio of ground substance to fibrous tissue. Loose connective tissue has much more ground substance and a relative lack of fibrous tissue, while the reverse is true of dense connective tissue.

===Loose connective tissue===
[[Loose connective tissue]] includes [[reticular connective tissue]], and [[adipose tissue]].

===Dense connective tissue===
[[Dense connective tissue]] also known as '''fibrous connective tissue'''<ref name="NCI2024">{{Cite web |date=2 February 2011 |title=Fibrous connective tissue |url=https://www.cancer.gov/publications/dictionaries/cancer-terms/def/fibrous-connective-tissue# |access-date=2 November 2024 |website=NCI Dictionary of Cancer Terms |publisher=National Cancer Institute |language=en}}</ref> is subdivided into [[dense regular connective tissue|dense regular]] and [[dense irregular connective tissue]].<ref>{{Cite web |last=Potter |first=Hugh |title=The Connective Tissues |url=http://faculty.ucc.edu/biology-potter/connective_tissues.htm |url-status=dead |archive-url=https://web.archive.org/web/20121031231335/http://faculty.ucc.edu/biology-potter/connective_tissues.htm |archive-date=31 October 2012 |access-date=9 December 2012}}</ref> Dense regular connective tissue, found in structures such as [[tendon]]s and [[ligament]]s, is characterized by [[collagen]] fibers arranged in an orderly parallel fashion, giving it tensile strength in one direction. Dense irregular connective tissue provides strength in multiple directions by its dense bundles of fibers arranged in all directions.{{cn|date=November 2022}}

===Special connective tissue===
'''Special connective tissue''' consists of [[cartilage]], [[bone]], [[blood]] and [[lymph]].<ref>{{Cite web |last=Caceci |first=Thomas |title=Connective Tisues |url=http://www.vetmed.vt.edu/education/curriculum/vm8054/labs/lab5/lab5.htm |url-status=dead |archive-url=https://archive.today/20130106123922/http://www.vetmed.vt.edu/education/curriculum/vm8054/labs/lab5/lab5.htm |archive-date=6 January 2013 |access-date=9 December 2012}}</ref> Other kinds of connective tissues include fibrous, elastic, and [[lymphatic system#Lymphoid tissue|lymphoid]] connective tissues.<ref>{{Cite news |last=King |first=David |title=Histology Intro |url=http://www.siumed.edu/~dking2/intro/ct.htm#ordinspecial |access-date=9 December 2012}}</ref> Fibroareolar tissue is a mix of fibrous and [[Loose connective tissue#Areolar tissue|areolar tissue]].<ref name="Merriam">{{Cite web |title=Medical Definition of FIBROAREOLAR |url=https://www.merriam-webster.com/medical/fibroareolar |access-date=11 October 2018 |website=Merriam-Webster |language=en}}</ref> Fibromuscular tissue is made up of fibrous tissue and [[muscle tissue|muscular tissue]]. New vascularised connective tissue that forms in the process of wound healing is termed [[granulation tissue]].<ref>{{Cite web |title=Granulation Tissue Definition |url=http://www.memidex.com/granulation-tissue |url-status=dead |archive-url=https://web.archive.org/web/20181116035707/http://www.memidex.com/granulation-tissue |archive-date=16 November 2018 |access-date=7 May 2016 |website=Memidex}}</ref> All of the special connective tissue types have been included as a subset of [[fascia]] in the ''fascial system'', with blood and lymph classed as ''liquid fascia''.<ref name="Bordoni">{{Cite journal |last=Bordoni |first=Bruno |last2=Mahabadi |first2=Navid |last3=Varacallo |first3=Matthew |date=2022 |title=Anatomy, Fascia |url=https://pubmed.ncbi.nlm.nih.gov/29630284/ |publisher=StatPearls Publishing |pmid=29630284 |access-date=3 August 2022 |website=StatPearls}}</ref><ref name="Schleip">{{Cite journal |last=Schleip |first=R |last2=Hedley |first2=G |last3=Yucesoy |first3=CA |date=October 2019 |title=Fascial nomenclature: Update on related consensus process. |journal=Clinical Anatomy |volume=32 |issue=7 |pages=929–933 |doi=10.1002/ca.23423 |pmc=6852276 |pmid=31183880}}</ref>

Bone and cartilage can be further classified as '''supportive''' '''connective tissue'''. Blood and lymph can also be categorized as '''fluid connective tissue''',<ref name="Biga">{{Citation |last=Biga |first=Lindsay M. |title=4.3 Connective Tissue Supports and Protects |date=2019 |work=Anatomy & Physiology |url=https://open.oregonstate.education/aandp/chapter/4-3-connective-tissue-supports-and-protects/ |access-date=2021-04-16 |publisher=OpenStax/Oregon State University |language=en |last2=Dawson |first2=Sierra |last3=Harwell |first3=Amy |last4=Hopkins |first4=Robin |last5=Kaufmann |first5=Joel |last6=LeMaster |first6=Mike |last7=Matern |first7=Philip |last8=Morrison-Graham |first8=Katie |last9=Quick |first9=Devon}}</ref><ref>{{Cite web |title=Supporting Connective Tissue {{!}} Human Anatomy and Physiology Lab (BSB 141) |url=https://courses.lumenlearning.com/ap1x94x1/chapter/supporting-connective-tissue/ |access-date=2021-04-16 |website=courses.lumenlearning.com}}</ref><ref>{{Cite web |last=Karki |first=Gaurab |date=2018-02-23 |title=Fluid or liquid connective tissue: blood and lymph |url=https://www.onlinebiologynotes.com/fluid-liquid-connective-tissue-blood-lymph/ |access-date=2021-04-16 |website=Online Biology Notes |language=en-US}}</ref> and ''liquid fascia''.<ref name="Bordoni" />

===Membranes===
[[Membrane]]s can be either of connective tissue or [[epithelial tissue]]. Connective tissue membranes include the [[meninges]] (the three membranes covering the [[brain]] and [[spinal cord]]) and [[synovial membrane]]s that line joint cavities.<ref name="SEER">{{Cite web |title=Membranes {{!}} SEER Training |url=https://training.seer.cancer.gov/anatomy/cells_tissues_membranes/membranes.html |access-date=3 August 2022 |website=training.seer.cancer.gov}}</ref> [[Mucous membrane]]s and [[serous membrane]]s are epithelial with an underlying layer of loose connective tissue.<ref name="SEER" />

==Fibrous types==
Fiber types found in the [[extracellular matrix]] are [[collagen fibers]], [[elastic fibers]], and [[reticular fibers]].<ref name="Ushiki">{{Cite journal |last=Ushiki |first=T |date=June 2002 |title=Collagen fibers, reticular fibers and elastic fibers. A comprehensive understanding from a morphological viewpoint. |journal=Archives of Histology and Cytology |volume=65 |issue=2 |pages=109–26 |doi=10.1679/aohc.65.109 |pmid=12164335 |doi-access=free}}</ref>
[[Ground substance]] is a clear, colorless, and viscous fluid containing [[glycosaminoglycan]]s and [[proteoglycan]]s allowing fixation of Collagen fibers in intercellular spaces. Examples of non-fibrous connective tissue include [[adipose tissue]] (fat) and [[blood]]. Adipose tissue gives "mechanical cushioning" to the body, among other functions.<ref>{{Cite journal |last=Xu, H. |display-authors=etal |year=2008 |title=Monitoring Tissue Engineering Using Magnetic Resonance Imaging |url=https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1053&context=biosysengfacpub |journal=Journal of Bioscience and Bioengineering |volume=106 |issue=6 |pages=515–527 |doi=10.1263/jbb.106.515 |pmid=19134545 |s2cid=3294995 |url-access=subscription}}</ref><ref>{{Cite journal |last=Laclaustra, M. |display-authors=etal |year=2007 |title=Metabolic syndrome pathophysiology: The role of adiposetissue |journal=Nutrition, Metabolism and Cardiovascular Diseases |volume=17 |issue=2 |pages=125–139 |doi=10.1016/j.numecd.2006.10.005 |pmc=4426988 |pmid=17270403}}</ref> Although there is no dense collagen network in adipose tissue, groups of adipose cells are kept together by collagen fibers and collagen sheets in order to keep fat tissue under compression in place (for example, the sole of the foot). Both the ground substance and proteins (fibers) create the matrix for connective tissue.

[[Type I collagen]] is present in many forms of connective tissue, and makes up about 25% of the total protein content of the mammalian body.<ref>{{Cite journal |last=Di Lullo |last2=G. A. |year=2002 |title=Mapping the Ligand-binding Sites and Disease-associated Mutations on the Most Abundant Protein in the Human, Type I Collagen |journal=Journal of Biological Chemistry |volume=277 |issue=6 |pages=4223–31 |doi=10.1074/jbc.M110709200 |pmid=11704682 |doi-access=free}}</ref>

{| class="wikitable"

|+Types of fibers
|-
! Tissue !! Purpose !! Components !! Location
|-
| [[Collagen fiber]]s || Bind bones and other tissues to each other || Alpha polypeptide chains || tendon, ligament, skin, cornea, cartilage, bone, blood vessels, gut, and intervertebral disc.
|-
| [[Elastic fiber]]s || Allow organs like arteries and lungs to recoil || Elastic microfibril and elastin  || extracellular matrix
|-
| [[Reticular fiber]]s || Form a scaffolding for other cells || Type III collagen || liver, bone marrow, and lymphatic organs
|}

==Function==
{{See also|Epithelial-mesenchymal transition}}
[[File:Hypermobility-10.jpg|thumb|Hypermobility as a result of an [[Ehlers-Danlos syndromes|inherited connective tissue defect]]]]

Connective tissue has a wide variety of functions that depend on the types of cells and the different classes of fibers involved. [[Loose connective tissue|Loose]] and [[dense irregular connective tissue]], formed mainly by [[fibroblast]]s and [[collagen|collagen fiber]]s, have an important role in providing a medium for oxygen and nutrients to diffuse from [[capillaries]] to cells, and carbon dioxide and waste substances to diffuse from cells back into circulation. They also allow organs to resist stretching and tearing forces. [[Dense regular connective tissue]], which forms organized structures, is a major functional component of [[tendon]]s, [[ligament]]s and [[aponeuroses]], and is also found in highly specialized organs such as the [[cornea]].<ref name="Ross">{{Cite book |last=Ross |first=Michael H. |title=Histology: a text and atlas ; with correlated cell and molecular biology |last2=Pawlina |first2=Wojciech |date=2011 |publisher=Lippincott Williams & Wilkins |isbn=978-0781772006 |edition=6., international |location=Philadelphia, Pa. London |pages=158–173}}</ref> [[Elastic fiber]]s, made from [[elastin]] and [[fibrillin]], also provide resistance to stretch forces.<ref name="Ross" /> They are found in the walls of large blood vessels and in certain ligaments, particularly in the [[ligamenta flava]].<ref name="Ross" />

In [[hematopoiesis|hematopoietic]] and [[lymphatic system|lymphatic]] tissues, [[reticular fiber]]s made by [[reticular cell]]s provide the [[Stroma (animal tissue)|stroma]]—or structural support—for the [[parenchyma]] (that is, the bulk of functional substance) of the organ.<ref name="Ross" />

[[Mesenchyme]] is a type of connective tissue found in the [[Organogenesis|developing organs]] of an [[embryo]] that is capable of [[cellular differentiation|differentiation]] into all types of mature connective tissue.<ref name="wheater">{{Cite book |title=Wheater's Functional Histology: A Text and Colour Atlas |vauthors=Young B, Woodford P, O'Dowd G |publisher=Elsevier |year=2013 |isbn=978-0702047473 |edition=6th |page=65}}</ref> Another type of relatively undifferentiated connective tissue is the '''mucous connective tissue''' known as [[Wharton's jelly]], found inside the [[umbilical cord]].<ref name="Ross" /> This tissue is no longer present after birth, leaving only scattered mesenchymal cells throughout the body.<ref name="Openstax Anatomy & Physiology attribution">{{CC-notice|cc=by4|url=https://openstax.org/books/anatomy-and-physiology/pages/4-3-connective-tissue-supports-and-protects}} {{Cite book |last=Betts |first=J Gordon |title=Anatomy & Physiology |last2=Desaix |first2=Peter |last3=Johnson |first3=Eddie |last4=Johnson |first4=Jody E |last5=Korol |first5=Oksana |last6=Kruse |first6=Dean |last7=Poe |first7=Brandon |last8=Wise |first8=James |last9=Womble |first9=Mark D |date=June 26, 2023 |publisher=OpenStax CNX |isbn=978-1-947172-04-3 |location=Houston |at=4.3 Connective Tissue supports and protects |last10=Young |first10=Kelly A}}</ref>

Various types of specialized tissues and cells are classified under the spectrum of connective tissue, and are as diverse as [[brown adipose tissue|brown]] and [[white adipose tissue]], [[blood]], [[cartilage]] and [[bone]].<ref name="Ross" /> Cells of the immune system—such as [[macrophage]]s, [[mast cell]]s, [[plasma cell]]s, and [[eosinophil]]s—are found scattered in loose connective tissue, providing the ground for starting [[inflammation|inflammatory]] and [[immune system|immune]] responses upon the detection of [[antigen]]s.<ref name="Ross" />

==Clinical significance==
{{Main|Connective tissue disease}}
There are many types of connective tissue disorders, such as:
* [[Connective tissue neoplasm]]s including [[sarcoma]]s such as [[hemangiopericytoma]] and [[malignant peripheral nerve sheath tumor]] in nervous tissue.
* [[Congenital disease]]s include [[Marfan syndrome]] and [[Ehlers-Danlos Syndrome]].
* [[Myxomatous degeneration]] – a pathological weakening of connective tissue.
* [[Mixed connective tissue disease]] – a disease of the [[autoimmune system]], also [[undifferentiated connective tissue disease]].
* [[Systemic lupus erythematosus]] (SLE) – a major autoimmune disease of connective tissue
* [[Scurvy]], caused by a deficiency of [[vitamin C]] which is necessary for the synthesis of collagen.
* [[Fibromuscular dysplasia]] is a [[vascular disease|disease of the blood vessels]] that leads to an abnormal growth in the arterial wall.

==See also==
* [[Endometrium]]
* [[Parametrium]]

== Notes and references ==
{{reflist}}

==External links==
{{Commons category|Connective tissues}}
* [http://www.kumc.edu/instruction/medicine/anatomy/histoweb/ct/ct.htm Overview, University of Kansas] {{Webarchive|url=https://web.archive.org/web/20101226050456/http://www.kumc.edu/instruction/medicine/anatomy/histoweb/ct/ct.htm |date=26 December 2010 }}
* [https://web.archive.org/web/20100727134405/http://www.medicine.uiowa.edu/anatomy/dental/genhisto/GHWIN/unit3/index.html Connective tissue atlas, University of Iowa]
* [https://web.archive.org/web/20150216072337/http://www.niams.nih.gov/Health_Info/Connective_Tissue/default.asp Heritable disorders of connective tissue] US National Institute of Arthritis and Musculoskeletal and Skin Diseases
* [http://www.histology-world.com/photoalbum/thumbnails.php?album=28 Connective tissue photomicrographs]

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