Editing Cartilage (section)

{{Short description|Resilient and smooth elastic tissue present in animals}}
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| Name          = Cartilage
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| Image         = Hypertrophic Zone of Epiphyseal Plate.jpg
| Caption       = Light [[micrograph]] of undecalcified [[hyaline cartilage]]  showing [[chondrocyte]]s and [[organelle]]s, [[Lacuna (histology)|lacunae]] and [[Extracellular matrix|matrix]].
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'''Cartilage''' is a resilient and smooth type of [[connective tissue]]. Semi-transparent and non-porous, it is usually covered by a tough and fibrous membrane called [[perichondrium]]. In tetrapods, it covers and protects the [[Epiphysis|ends]] of [[long bone]]s at the [[joint]]s as [[articular cartilage]],<ref name="Fox">{{cite journal |last1=Sophia Fox |first1=AJ |last2=Bedi |first2=A |last3=Rodeo |first3=SA |title=The basic science of articular cartilage: structure, composition, and function. |journal=Sports Health |date=November 2009 |volume=1 |issue=6 |pages=461–8 |doi=10.1177/1941738109350438 |pmid=23015907|pmc=3445147 }}</ref> and is a structural component of many body parts including the [[rib cage]], the neck and the bronchial tubes, and the [[intervertebral disc]]s. In other taxa, such as [[Chondrichthyes|chondrichthyans]] and [[Cyclostomi|cyclostomes]], it constitutes a much greater proportion of the skeleton.<ref name="de Buffrénil et al. 2021">{{cite book |last1=de Buffrénil |first1=Vivian |last2=de Ricqlès |first2=Armand J |last3=Zylberberg |first3=Louise |last4=Padian |first4=Kevin |last5=Laurin |first5=Michel |last6=Quilhac |first6=Alexandra |title=Vertebrate skeletal histology and paleohistology |date=2021 |publisher=CRC Press |location=Boca Raton, FL |isbn=978-1351189576 |pages=xii + 825 |edition=Firstiton |url=https://books.google.com/books?id=tJcwEAAAQBAJ&pg=PT8}}</ref> It is not as hard and rigid as [[bone]], but it is much stiffer and much less flexible than [[muscle]]. The matrix of cartilage is made up of [[glycosaminoglycan]]s, [[proteoglycan]]s, [[collagen]] fibers and, sometimes, [[elastin]]. It usually grows quicker than bone.

Because of its rigidity, cartilage often serves the purpose of holding tubes open in the body. Examples include the rings of the trachea, such as the [[cricoid cartilage]] and [[Carina of trachea|carina]].

Cartilage is composed of specialized cells called [[chondrocyte]]s that produce a large amount of collagenous [[extracellular matrix]], abundant [[ground substance]] that is rich in proteoglycan and elastin fibers. Cartilage is classified into three types {{emdash}} [[elastic cartilage]], [[hyaline cartilage]], and [[fibrocartilage]] {{emdash}} which differ in their relative amounts of collagen and proteoglycan.

As cartilage does not contain [[blood]] vessels or [[nerve]]s, it is insensitive. However, some fibrocartilage such as the [[Meniscus (anatomy)|meniscus]] of the [[knee]] has partial blood supply. Nutrition is supplied to the chondrocytes by [[diffusion]]. The compression of the articular cartilage or flexion of the elastic cartilage generates fluid flow, which assists the diffusion of nutrients to the chondrocytes. Compared to other connective tissues, cartilage has a very slow turnover of its extracellular matrix and is documented to repair at only a very slow rate relative to other tissues.

[[File:Cartilage types.jpg|thumb|upright=1.3|There are three different types of cartilage: elastic (A), hyaline (B), and fibrous (C). In elastic cartilage, the cells are closer together creating less intercellular space. Elastic cartilage is found in the external ear flaps and in parts of the larynx. Hyaline cartilage has fewer cells than elastic cartilage; there is more intercellular space. Hyaline cartilage is found in the nose, ears, trachea, parts of the larynx, and smaller respiratory tubes. Fibrous cartilage has the fewest cells so it has the most intercellular space. Fibrous cartilage is found in the spine and the menisci.]]
[[File:Prionace glauca cartilage.jpg|thumb|The physical appearance of cartilage]]