The term "connective tissue" (in German,Bindegewebe) was introduced in 1830 byJohannes Peter Müller. The tissue was already recognized as a distinct class in the 18th century.[4][5]
Connective tissue can be broadly classified into connective tissue proper, and special connective tissue.[6][7] 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.
Dense connective tissue also known asfibrous connective tissue[8] is subdivided intodense regular anddense irregular connective tissue.[9] Dense regular connective tissue, found in structures such astendons andligaments, is characterized bycollagen 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.[citation needed]
Special connective tissue consists ofcartilage,bone,blood andlymph.[10] Other kinds of connective tissues include fibrous, elastic, andlymphoid connective tissues.[11] Fibroareolar tissue is a mix of fibrous andareolar tissue.[12] Fibromuscular tissue is made up of fibrous tissue andmuscular tissue. New vascularised connective tissue that forms in the process of wound healing is termedgranulation tissue.[13] All of the special connective tissue types have been included as a subset offascia in thefascial system, with blood and lymph classed asliquid fascia.[14][15]
Bone and cartilage can be further classified assupportiveconnective tissue. Blood and lymph can also be categorized asfluid connective tissue,[2][16][17] andliquid fascia.[14]
Fiber types found in theextracellular matrix arecollagen fibers,elastic fibers, andreticular fibers.[19]Ground substance is a clear, colorless, and viscous fluid containingglycosaminoglycans andproteoglycans allowing fixation of Collagen fibers in intercellular spaces. Examples of non-fibrous connective tissue includeadipose tissue (fat) andblood. Adipose tissue gives "mechanical cushioning" to the body, among other functions.[20][21] 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.[22]
Connective tissue has a wide variety of functions that depend on the types of cells and the different classes of fibers involved.Loose anddense irregular connective tissue, formed mainly byfibroblasts andcollagen fibers, have an important role in providing a medium for oxygen and nutrients to diffuse fromcapillaries 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 oftendons,ligaments andaponeuroses, and is also found in highly specialized organs such as thecornea.[23]Elastic fibers, made fromelastin andfibrillin, also provide resistance to stretch forces.[23] They are found in the walls of large blood vessels and in certain ligaments, particularly in theligamenta flava.[23]
Mesenchyme is a type of connective tissue found in thedeveloping organs of anembryo that is capable ofdifferentiation into all types of mature connective tissue.[24] Another type of relatively undifferentiated connective tissue is themucous connective tissue known asWharton's jelly, found inside theumbilical cord.[23] This tissue is no longer present after birth, leaving only scattered mesenchymal cells throughout the body.[25]
^Mathews, M. B. (1975).Connective Tissue, Macromolecular Structure Evolution. Springer-Verlag, Berlin and New York.link.
^Aterman, K. (1981). "Connective tissue: An eclectic historical review with particular reference to the liver".The Histochemical Journal.13 (3):341–396.doi:10.1007/BF01005055.PMID7019165.S2CID22765625.
^abcdefgRoss, Michael H.; Pawlina, Wojciech (2011).Histology: a text and atlas ; with correlated cell and molecular biology (6., international ed.). Philadelphia, Pa. London: Lippincott Williams & Wilkins. pp. 158–173.ISBN978-0781772006.
^Young B, Woodford P, O'Dowd G (2013).Wheater's Functional Histology: A Text and Colour Atlas (6th ed.). Elsevier. p. 65.ISBN978-0702047473.
^ This article incorporatestext available under theCC BY 4.0 license.Betts, J Gordon; Desaix, Peter; Johnson, Eddie; Johnson, Jody E; Korol, Oksana; Kruse, Dean; Poe, Brandon; Wise, James; Womble, Mark D; Young, Kelly A (26 June 2023).Anatomy & Physiology. Houston: OpenStax CNX. 4.3 Connective Tissue supports and protects.ISBN978-1-947172-04-3.
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