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{{Short description|Resilient and smooth elastic tissue present in animals}} {{Infobox anatomy | Name = Cartilage | Pronunciation = | Synonyms = | 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]]. | Width = | Image2 = | Caption2 = | Latin = | Greek = | Precursor = | System = | Artery = | Vein = | Nerve = | Lymph = }} '''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]] == Structure == === Development === {{Main|Chondrogenesis}} In [[embryogenesis]], the [[skeletal]] system is derived from the [[mesoderm]] germ layer. Chondrification (also known as chondrogenesis) is the process by which cartilage is formed from condensed [[mesenchyme]] tissue, which differentiates into [[chondroblast]]s and begins secreting the molecules ([[aggrecan]] and collagen type II) that form the extracellular matrix. In all vertebrates, cartilage is the main skeletal tissue in early ontogenetic stages;<ref>{{cite journal |last1=Buffrénil |first1=Vivian de |last2=Quilhac |first2=Alexandra |title=An Overview of the Embryonic Development of the Bony Skeleton |journal=Vertebrate Skeletal Histology and Paleohistology |date=2021 |pages=29–38 |doi=10.1201/9781351189590-2 |url=https://www.taylorfrancis.com/chapters/edit/10.1201/9781351189590-2/overview-embryonic-development-bony-skeleton-vivian-de-buffr%C3%A9nil-alexandra-quilhac |publisher=CRC Press|isbn=9781351189590 |s2cid=236422314 |url-access=subscription }}</ref><ref>{{cite journal |last1=Quilhac |first1=Alexandra |title=An Overview of Cartilage Histology |journal=Vertebrate Skeletal Histology and Paleohistology |date=2021 |pages=123–146 |doi=10.1201/9781351189590-7 |url=https://www.taylorfrancis.com/chapters/edit/10.1201/9781351189590-7/overview-cartilage-histology-alexandra-quilhac |publisher=CRC Press|isbn=9781351189590 |s2cid=236413810 |url-access=subscription }}</ref> in osteichthyans, many cartilaginous elements subsequently ossify through [[endochondral]] and perichondral ossification.<ref>{{cite journal |last1=Cervantes-Diaz |first1=Fret |last2=Contreras |first2=Pedro |last3=Marcellini |first3=Sylvain |title=Evolutionary origin of endochondral ossification: the transdifferentiation hypothesis |journal=Development Genes and Evolution |date=March 2017 |volume=227 |issue=2 |pages=121–127 |doi=10.1007/s00427-016-0567-y|pmid=27909803 |s2cid=21024809 }}</ref> Following the initial chondrification that occurs during embryogenesis, cartilage growth consists mostly of the maturing of immature cartilage to a more mature state. The division of cells within cartilage occurs very slowly, and thus growth in cartilage is usually not based on an increase in size or mass of the cartilage itself.<ref>{{cite journal | vauthors = Asanbaeva A, Masuda K, Thonar EJ, Klisch SM, Sah RL | title = Cartilage growth and remodeling: modulation of balance between proteoglycan and collagen network in vitro with beta-aminopropionitrile | journal = Osteoarthritis and Cartilage | volume = 16 | issue = 1 | pages = 1–11 | date = January 2008 | pmid = 17631390 | doi = 10.1016/j.joca.2007.05.019 | url = https://digitalcommons.calpoly.edu/cgi/viewcontent.cgi?article=1015&context=meng_fac | doi-access = free }}</ref> It has been identified that non-coding RNAs (e.g. miRNAs and long non-coding RNAs) as the most important epigenetic modulators can affect the chondrogenesis. This also justifies the non-coding RNAs' contribution in various cartilage-dependent pathological conditions such as arthritis, and so on.<ref>{{cite journal | vauthors = Razmara E, Bitaraf A, Yousefi H, Nguyen TH, Garshasbi M, Cho WC, Babashah S | title = Non-Coding RNAs in Cartilage Development: An Updated Review | journal = International Journal of Molecular Sciences | volume = 20 | issue = 18 | pages = 4475 | date = September 2019 | pmid = 31514268 | pmc = 6769748 | doi = 10.3390/ijms20184475 | doi-access = free }}</ref> === Articular cartilage === {{rewrite section|date=April 2025}} [[File:Cartilage from mouse joint.jpg|thumb|Section from mouse joint showing cartilage (purple)]] The articular cartilage function is dependent on the molecular composition of the [[extracellular matrix]] (ECM). The ECM consists mainly of [[proteoglycan]] and [[collagen]]s. The main proteoglycan in cartilage is aggrecan, which, as its name suggests, forms large aggregates with [[hyaluronan]] and with itself.<ref name="Chremos2023">{{cite journal | vauthors = Chremos A, Horkay F | title = Coexistence of Crumpling and Flat Sheet Conformations in Two-Dimensional Polymer Networks: An Understanding of Aggrecan Self-Assembly | journal = Physical Review Letters | volume = 131 | pages = 138101 | date = September 2023 | issue = 13 | doi = 10.1103/PhysRevLett.131.138101 | pmid = 37832020 | bibcode = 2023PhRvL.131m8101C | s2cid = 263252529 }}</ref> These aggregates are negatively charged and hold water in the tissue. The collagen, mostly collagen type II, constrains the proteoglycans. The ECM responds to tensile and compressive forces that are experienced by the cartilage.<ref>{{cite journal | vauthors = Asanbaeva A, Tam J, Schumacher BL, Klisch SM, Masuda K, Sah RL | title = Articular cartilage tensile integrity: modulation by matrix depletion is maturation-dependent | journal = Archives of Biochemistry and Biophysics | volume = 474 | issue = 1 | pages = 175–82 | date = June 2008 | pmid = 18394422 | pmc = 2440786 | doi = 10.1016/j.abb.2008.03.012 }}</ref> Cartilage growth thus refers to the matrix deposition, but can also refer to both the growth and remodeling of the extracellular matrix. Due to the great stress on the patellofemoral joint during resisted knee extension, the articular cartilage of the patella is among the thickest in the human body. The ECM of articular cartilage is classified into three regions: the pericellular matrix, the [[territorial matrix]], and the interterritorial matrix. == Function == === Mechanical properties === The mechanical properties of articular cartilage in load-bearing joints such as the [[knee]] and [[hip]] have been studied extensively at macro, micro, and nano-scales. These mechanical properties include the response of cartilage in frictional, compressive, shear and tensile loading. Cartilage is resilient and displays [[Viscoelasticity|viscoelastic]] properties.<ref name="pmid5111002">{{cite journal | vauthors = Hayes WC, Mockros LF | title = Viscoelastic properties of human articular cartilage | journal = Journal of Applied Physiology | volume = 31 | issue = 4 | pages = 562–8 | date = October 1971 | pmid = 5111002 | doi = 10.1152/jappl.1971.31.4.562 | url = http://jap.physiology.org/content/31/4/562.full.pdf }}</ref> Since cartilage has interstitial fluid that is free-moving, it makes the material difficult to test. One of the tests commonly used to overcome this obstacle is a confined compression test, which can be used in either a 'creep' or 'relaxation' mode.<ref name="mansour2013">{{cite book | last=Mansour | first=J. M. | date=2013 | title=Biomechanics of Cartilage | pages=69–83}}</ref><ref name="patel2019">{{cite journal |last1=Patel |first1=J. M. |last2=Wise |first2=B. C. |last3=Bonnevie |first3=E. D. |last4=Mauck |first4=R. L. |date=2019 |title=A Systematic Review and Guide to Mechanical Testing for Articular Cartilage Tissue Engineering |url=https://doi.org/10.1089/ten.tec.2019.0116 |journal=Tissue Eng Part C Methods |volume=25 |issue=10 |pages=593–608|doi=10.1089/ten.tec.2019.0116 |pmid=31288616 |pmc=6791482 }}</ref> In creep mode, the tissue displacement is measured as a function of time under a constant load, and in relaxation mode, the force is measured as a function of time under constant displacement. During this mode, the deformation of the tissue has two main regions. In the first region, the displacement is rapid due to the initial flow of fluid out of the cartilage, and in the second region, the displacement slows down to an eventual constant equilibrium value. Under the commonly used loading conditions, the equilibrium displacement can take hours to reach. In both the creep mode and the relaxation mode of a confined compression test, a disc of cartilage is placed in an impervious, fluid-filled container and covered with a porous plate that restricts the flow of interstitial fluid to the vertical direction. This test can be used to measure the aggregate modulus of cartilage, which is typically in the range of 0.5 to 0.9 MPa for articular cartilage,<ref name="mansour2013"></ref><ref name="patel2019"></ref><ref name="korhonen2002">{{cite journal |last1=Korhonen |first1=R. K. |last2=Laasanen |first2=M. S. |last3=Töyräs |first3=J. |last4=Rieppo |first4=J. |last5=Hirvonen |first5=J. |last6=Helminen |first6=H. J. |last7=Jurvelin |first7=J. S. |date=2002 |title=Comparison of the Equilibrium Response of Articular Cartilage in Unconfined Compression, Confined Compression and Indentation |url=https://doi.org/10.1016/S0021-9290(02)00052-0 |journal=Journal of Biomechanics |volume=35 |issue=7 |pages=903–909|doi=10.1016/S0021-9290(02)00052-0 |pmid=12052392 |url-access=subscription }}</ref> and the Young’s Modulus, which is typically 0.45 to 0.80 MPa.<ref name="mansour2013"></ref><ref name="korhonen2002"></ref> The aggregate modulus is "a measure of the stiffness of the tissue at equilibrium when all fluid flow has ceased",<ref name="mansour2013"></ref> and Young’s modulus is a measure of how much a material strains (changes length) under a given stress. The confined compression test can also be used to measure permeability, which is defined as the resistance to fluid flow through a material. Higher permeability allows for fluid to flow out of a material’s matrix more rapidly, while lower permeability leads to an initial rapid fluid flow and a slow decrease to equilibrium. Typically, the permeability of articular cartilage is in the range of 10^-15 to 10^-16 m^4/Ns.<ref name="mansour2013"></ref><ref name="patel2019"></ref> However, permeability is sensitive to loading conditions and testing location. For example, permeability varies throughout articular cartilage and tends to be highest near the joint surface and lowest near the bone (or "deep zone"). Permeability also decreases under increased loading of the tissue. Indentation testing is an additional type of test commonly used to characterize cartilage.<ref name="mansour2013"></ref><ref name="kabir2021">{{cite journal |last1=Kabir |first1=W. |last2=Di Bella |first2=C. |last3=Choong |first3=P. F. M. |last4=O’Connell |first4=C. D. |date=2021 |title=Assessment of Native Human Articular Cartilage: A Biomechanical Protocol |url=https://doi.org/10.1177/1947603520973240 |journal=Cartilage |volume=13 |issue=2 Suppl |pages=427S–437S|doi=10.1177/1947603520973240 |pmid=33218275 |pmc=8804788 }}</ref> Indentation testing involves using an indentor (usually <0.8 mm) to measure the displacement of the tissue under constant load. Similar to confined compression testing, it may take hours to reach equilibrium displacement. This method of testing can be used to measure the aggregate modulus, Poisson's ratio, and permeability of the tissue. Initially, there was a misconception that due to its predominantly water-based composition, cartilage had a Poisson's ratio of 0.5 and should be modeled as an incompressible material.<ref name="mansour2013"></ref> However, subsequent research has disproven this belief. The Poisson’s ratio of articular cartilage has been measured to be around 0.4 or lower in humans <ref name="mansour2013"></ref><ref name="kabir2021"></ref> and ranges from 0.46–0.5 in bovine subjects.<ref name="jin2004">{{cite journal |last1=Jin |first1=H. |last2=Lewis |first2=J. L. |date=2004 |title=Determination of Poisson's Ratio of Articular Cartilage by Indentation Using Different-Sized Indenters |url=https://doi.org/10.1115/1.1688772 |journal=Journal of Biomechanical Engineering |volume=126 |issue=2 |pages=138–145|doi=10.1115/1.1688772 |pmid=15179843 |url-access=subscription }}</ref> The mechanical properties of articular cartilage are largely anisotropic, test-dependent, and can be age-dependent.<ref name="mansour2013"></ref> These properties also depend on collagen-proteoglycan interactions and therefore can increase/decrease depending on the total content of water, collagen, glycoproteins, etc. For example, increased glucosaminoglycan content leads to an increase in compressive stiffness, and increased water content leads to a lower aggregate modulus. === Tendon-bone interface === In addition to its role in load-bearing joints, cartilage serves a crucial function as a gradient material between softer tissues and bone. Mechanical gradients are crucial for your body’s function, and for complex artificial structures including joint implants. Interfaces with mismatched material properties lead to areas of high [[stress concentration]] which, over the millions of loading cycles experienced by human joins over a lifetime, would eventually lead to failure. For example, the elastic modulus of human bone is roughly 20 GPa while the softer regions of cartilage can be about 0.5 to 0.9 MPa. <ref>{{cite journal |last1=Handorf |first1=Andrew |title=Tissue Stiffness Dictates Development, Homeostasis, and Disease Progression |journal=Organogensis |date=27 April 2015 |volume=11 |issue=1 |pages=1–15 |doi=10.1080/15476278.2015.1019687 |pmid=25915734 |pmc=4594591 }}</ref><ref>{{cite book |last1=Mansour |first1=Joseph |title=Biomechanics of Cartilage |publisher=MDPI |pages=66–79 |url=https://web.mit.edu/cortiz/www/3.052/3.052CourseReader/27_BiomechanicsofCartilage.pdf}}</ref> When there is a smooth gradient of materials properties, however, stresses are distributed evenly across the interface, which puts less wear on each individual part. The body solves this problem with stiffer, higher modulus layers near bone, with high concentrations of mineral deposits such as hydroxyapatite. Collagen fibers (which provide mechanical stiffness in cartilage) in this region are anchored directly to bones, reducing the possible deformation. Moving closer to soft tissue into the region known as the tidemark, the density of [[chondrocytes]] increases and collagen fibers are rearranged to optimize for stress dissipation and low friction. The outermost layer near the articular surface is known as the superficial zone, which primarily serves as a lubrication region. Here cartilage is characterized by a dense extracellular matrix and is rich in proteoglycans (which dispel and reabsorb water to soften impacts) and thin collagen oriented parallel to the joint surface which have excellent shear resistant properties. <ref>{{cite journal |last1=Chen |first1=Li |title=Preparation and Characterization of Biomimetic Functional Scaffold with Gradient Structure for Osteochondral Defect Repair |journal=Bioengineering |date=6 February 2023 |volume=10 |issue=2 |page=213 |doi=10.3390/bioengineering10020213 |doi-access=free |pmid=36829707 |pmc=9952804 }}</ref> Osteoarthritis and natural aging both have negative effects on cartilage as a whole as well as the proper function of the materials gradient within. The earliest changes are often in the superficial zone, the softest and most lubricating part of the tissue. Degradation of this layer can put additional stresses on deeper layers which are not designed to support the same deformations. Another common effect of aging is increased crosslinking of collagen fibers. This leads to stiffer cartilage as a whole, which again can lead to early failure as stiffer tissue is more susceptible to fatigue based failure. Aging in calcified regions also generally leads to a larger number of mineral deposits, which has a similarly undesired stiffening effect. <ref>{{cite journal |last1=Lotz |first1=Martin |title=Effects of aging on articular cartilage homeostasis |journal=Bone |date=28 March 2012 |volume=51 |issue=2 |pages=241–248 |doi=10.1016/j.bone.2012.03.023 |pmid=22487298 |pmc=3372644 }}</ref> Osteoarthritis has more extreme effects and can entirely wear down cartilage, causing direct bone-to-bone contact.<ref>{{cite web |title=Osteoarthritis |url=https://www.mayoclinic.org/diseases-conditions/osteoarthritis/symptoms-causes/syc-20351925 |website=Mayo Clinic |access-date=13 May 2024}}</ref> === Frictional properties === [[Lubricin]], a [[glycoprotein]] abundant in cartilage and [[synovial fluid]], plays a major role in bio-lubrication and wear protection of cartilage.<ref name=Rhee2005>{{cite journal | vauthors = Rhee DK, Marcelino J, Baker M, Gong Y, Smits P, Lefebvre V, Jay GD, Stewart M, Wang H, Warman ML, Carpten JD | display-authors = 6 | title = The secreted glycoprotein lubricin protects cartilage surfaces and inhibits synovial cell overgrowth | journal = The Journal of Clinical Investigation | volume = 115 | issue = 3 | pages = 622–31 | date = March 2005 | pmid = 15719068 | pmc = 548698 | doi = 10.1172/JCI22263 }}</ref> === Repair === Cartilage has limited repair capabilities: Because chondrocytes are bound in [[Lacuna (histology)|lacunae]], they cannot migrate to damaged areas. Therefore, [[cartilage damage]] is difficult to heal. Also, because hyaline cartilage does not have a blood supply, the deposition of new matrix is slow. Over the last years, surgeons and scientists have elaborated a series of [[articular cartilage repair|cartilage repair procedures]] that help to postpone the need for joint replacement. A [[Tear of meniscus|tear of the meniscus]] of the knee cartilage can often be surgically trimmed to reduce problems. Complete healing of cartilage after injury or repair procedures is hindered by cartilage-specific inflammation caused by the involvement of M1/M2 [[Macrophage|macrophages]], [[Mast cell|mast cells]], and their intercellular interactions.<ref>{{Cite journal |last1=Klabukov |first1=I. |last2=Atiakshin |first2=D. |last3=Kogan |first3=E. |last4=Ignatyuk |first4=M. |last5=Krasheninnikov |first5=M. |last6=Zharkov |first6=N. |last7=Yakimova |first7=A. |last8=Grinevich |first8=V. |last9=Pryanikov |first9=P. |last10=Parshin |first10=V. |last11=Sosin |first11=D. |last12=Kostin |first12=A.A. |last13=Shegay |first13=P. |last14=Kaprin |first14=A.D. |last15=Baranovskii |first15=D. |date=2023 |title=Post-Implantation Inflammatory Responses to Xenogeneic Tissue-Engineered Cartilage Implanted in Rabbit Trachea: The Role of Cultured Chondrocytes in the Modification of Inflammation |journal=International Journal of Molecular Sciences |volume=24 |issue=23 |pages=16783 |doi=10.3390/ijms242316783 |doi-access=free |issn=1422-0067 |pmc=10706106 |pmid=38069106}}</ref> [[Biological engineering]] techniques are being developed to generate new cartilage, using a cellular "scaffolding" material and [[Autologous chondrocyte implantation|cultured cells]] to grow artificial cartilage.<ref>[http://www.cartilage.org International Cartilage Repair Society ICRS]</ref> Extensive researches have been conducted on freeze-thawed [[Polyvinyl alcohol|PVA]] [[hydrogel]]s as a base material for such a purpose.<ref name=":0">{{Cite journal|last1=Adelnia|first1=Hossein|last2=Ensandoost|first2=Reza|last3=Shebbrin Moonshi|first3=Shehzahdi|last4=Gavgani|first4=Jaber Nasrollah|last5=Vasafi|first5=Emad Izadi|last6=Ta|first6=Hang Thu|date=2022-02-05|title=Freeze/thawed polyvinyl alcohol hydrogels: Present, past and future|url=https://www.sciencedirect.com/science/article/pii/S0014305721007084|journal=European Polymer Journal|language=en|volume=164|pages=110974|doi=10.1016/j.eurpolymj.2021.110974|bibcode=2022EurPJ.16410974A |s2cid=245576810|issn=0014-3057|hdl=10072/417476|hdl-access=free}}</ref> These gels have exhibited great promises in terms of biocompatibility, wear resistance, [[shock absorption]], [[friction]] coefficient, [[Stiffness|flexibility]], and lubrication, and thus are considered superior to polyethylene-based cartilages. A two-year implantation of the PVA hydrogels as artificial meniscus in rabbits showed that the gels remain intact without degradation, fracture, or loss of properties.<ref name=":0" /> == Clinical significance == [[File:Skeleton 1 -- Smart-Servier.png|thumb|upright|Human skeleton with articular cartilage shown in blue]] === Disease === {{Main|Chondropathy}} Several diseases can affect cartilage. [[Chondrodystrophies]] are a group of diseases, characterized by the disturbance of growth and subsequent [[ossification]] of cartilage. Some common diseases that affect the cartilage are listed below. * [[Osteoarthritis]]: Osteoarthritis is a disease of the whole joint, however, one of the most affected tissues is the articular cartilage. The cartilage covering bones (articular cartilage—a subset of hyaline cartilage) is thinned, eventually completely wearing away, resulting in a "bone against bone" within the joint, leading to reduced motion, and pain. Osteoarthritis affects the joints exposed to high stress and is therefore considered the result of "wear and tear" rather than a true disease. It is treated by [[arthroplasty]], the replacement of the joint by a synthetic joint often made of a stainless steel alloy ([[cobalt]] chromoly) and [[ultra-high-molecular-weight polyethylene]]. [[Chondroitin sulfate]] or [[glucosamine]] sulfate supplements, have been claimed to reduce the symptoms of osteoarthritis, but there is little good evidence to support this claim.<ref>{{Cite news | url=https://www.bbc.co.uk/news/health-11330747 | work=BBC News | title=Supplements for osteoarthritis 'do not work' | date=16 September 2010}}</ref> In osteoarthritis, increased expression of inflammatory cytokines and chemokines cause aberrant changes in differentiated chondrocytes function which leads to an excess of chondrocyte catabolic activity, mediated by factors including matrix [[metalloproteinase]]s and [[aggrecanase]]s.<ref>{{Cite journal |last1=Ansari |first1=Mohammad Y. |last2=Ahmad |first2=Nashrah |last3=Haqqi |first3=Tariq M. |date=2018-09-05 |title=Butein Activates Autophagy Through AMPK/TSC2/ULK1/mTOR Pathway to Inhibit IL-6 Expression in IL-1β Stimulated Human Chondrocytes |journal=Cellular Physiology and Biochemistry |volume=49 |issue=3 |pages=932–946 |doi=10.1159/000493225 |pmid=30184535 |s2cid=52166938 |issn=1015-8987|doi-access=free }}</ref> * Traumatic rupture or detachment: The cartilage in the knee is frequently damaged but can be partially repaired through [[knee cartilage replacement therapy]]. Often when athletes talk of damaged "cartilage" in their knee, they are referring to a damaged meniscus (a [[fibrocartilage]] structure) and not the articular cartilage. * [[Achondroplasia]]: Reduced proliferation of chondrocytes in the epiphyseal plate of long bones during infancy and childhood, resulting in [[dwarfism]]. * [[Costochondritis]]: Inflammation of cartilage in the ribs, causing [[chest pain]]. * [[Spinal disc herniation]]: Asymmetrical compression of an [[intervertebral disc]] ruptures the sac-like disc, causing a [[hernia]]tion of its soft content. The hernia often compresses the adjacent nerves and causes back pain. * [[Relapsing polychondritis]]: a destruction, probably [[autoimmune]], of cartilage, especially of the nose and ears, causing disfiguration. Death occurs by [[asphyxia]]tion as the larynx loses its rigidity and collapses. [[Neoplasm|Tumors]] made up of cartilage tissue, either [[benign tumor|benign]] or [[cancer|malignant]], can occur. They usually appear in bone, rarely in pre-existing cartilage. The benign tumors are called [[chondroma]], the malignant ones [[chondrosarcoma]]. Tumors arising from other tissues may also produce a cartilage-like matrix, the best-known being [[pleomorphic adenoma]] of the [[salivary gland]]s. The matrix of cartilage acts as a barrier, preventing the entry of [[lymphocyte]]s or diffusion of [[immunoglobulins]]. This property allows for the [[Organ transplantation|transplantation]] of cartilage from one individual to another without fear of tissue rejection. === Imaging === Cartilage does not absorb [[X-ray]]s under normal ''[[in vivo]]'' conditions, but a dye can be injected into the [[synovial membrane]] that will cause the {{nowrap|X-rays}} to be absorbed by the dye. The resulting void on the [[radiographic]] film between the bone and meniscus represents the cartilage. For [[in vitro]] {{nowrap|X-ray}} scans, the outer soft tissue is most likely removed, so the cartilage and air boundary are enough to contrast the presence of cartilage due to the [[refraction]] of the {{nowrap|X-ray}}.<ref>[http://osteoarthritis.about.com/od/osteoarthritis101/a/cartilage.htm Osteoarthritis] {{Webarchive|url=https://web.archive.org/web/20110707075030/http://osteoarthritis.about.com/od/osteoarthritis101/a/cartilage.htm |date=2011-07-07 }}. Osteoarthritis.about.com. Retrieved on 2015-10-26.</ref> [[File:Cartilage polarised.jpg|upright=1.4|thumb|Histological image of [[hyaline cartilage]] stained with [[H&E stain|haematoxylin and eosin]], under polarized light]] == Other animals == === Cartilaginous fish === Cartilaginous fish ([[Chondrichthyes]]) or [[shark]]s, [[Batoidea|ray]]s and [[chimaera]]s have a skeleton composed entirely of cartilage. === Invertebrate cartilage === Cartilage tissue can also be found among some arthropods such as [[horseshoe crab]]s, some mollusks such as marine [[snail]]s and [[cephalopod]]s, and some annelids like sabellid polychaetes. ====Arthropods==== The most studied cartilage in arthropods is the branchial cartilage of ''[[Limulus polyphemus]]''. It is a vesicular cell-rich cartilage due to the large, spherical and vacuolated chondrocytes with no homologies in other arthropods. Other type of cartilage found in ''L. polyphemus'' is the endosternite cartilage, a fibrous-hyaline cartilage with chondrocytes of typical morphology in a fibrous component, much more fibrous than vertebrate hyaline cartilage, with [[mucopolysaccharide]]s immunoreactive against chondroitin sulfate antibodies. There are homologous tissues to the endosternite cartilage in other arthropods.<ref name="ColeHall2004">{{cite journal | vauthors = Cole AG, Hall BK | title = The nature and significance of invertebrate cartilages revisited: distribution and histology of cartilage and cartilage-like tissues within the Metazoa | journal = Zoology | volume = 107 | issue = 4 | pages = 261–73 | year = 2004 | pmid = 16351944 | doi = 10.1016/j.zool.2004.05.001 | bibcode = 2004Zool..107..261C }}</ref> The embryos of ''Limulus polyphemus'' express ColA and hyaluronan in the gill cartilage and the endosternite, which indicates that these tissues are fibrillar-collagen-based cartilage. The endosternite cartilage forms close to Hh-expressing ventral nerve cords and expresses ColA and SoxE, a Sox9 analog. This is also seen in gill cartilage tissue.<ref name="TarazonaEtAl2016">{{cite journal | vauthors = Tarazona OA, Slota LA, Lopez DH, Zhang G, Cohn MJ | title = The genetic program for cartilage development has deep homology within Bilateria | journal = Nature | volume = 533 | issue = 7601 | pages = 86–9 | date = May 2016 | pmid = 27111511 | doi = 10.1038/nature17398 | bibcode = 2016Natur.533...86T | s2cid = 3932905 }}</ref> ====Mollusks==== In cephalopods, the models used for the studies of cartilage are ''[[Octopus vulgaris]]'' and ''[[Sepia officinalis]]''. The cephalopod cranial cartilage is the invertebrate cartilage that shows more resemblance to the vertebrate hyaline cartilage. The growth is thought to take place throughout the movement of cells from the periphery to the center. The chondrocytes present different morphologies related to their position in the tissue.<ref name="ColeHall2004" /> The embryos of ''S. officinalis'' express ColAa, ColAb, and hyaluronan in the cranial cartilages and other regions of chondrogenesis. This implies that the cartilage is fibrillar-collagen-based. The ''S. officinalis'' embryo expresses hh, whose presence causes ColAa and ColAb expression and is also able to maintain proliferating cells undiferentiated. It has been observed that this species presents the expression SoxD and SoxE, analogs of the vertebrate Sox5/6 and Sox9, in the developing cartilage. The cartilage growth pattern is the same as in vertebrate cartilage.<ref name="TarazonaEtAl2016" /> In gastropods, the interest lies in the [[odontophore]], a cartilaginous structure that supports the radula. The most studied species regarding this particular tissue is ''[[Busycotypus canaliculatus]]''. The odontophore is a vesicular cell rich cartilage, consisting of vacuolated cells containing myoglobin, surrounded by a low amount of extra cellular matrix containing collagen. The odontophore contains muscle cells along with the chondrocytes in the case of ''[[Lymnaea]]'' and other mollusks that graze vegetation.<ref name="ColeHall2004" /> ====Sabellid polychaetes==== The [[Sabellidae|sabellid polychaetes]], or feather duster worms, have cartilage tissue with cellular and matrix specialization supporting their tentacles. They present two distinct extracellular matrix regions. These regions are an acellular fibrous region with a high collagen content, called cartilage-like matrix, and collagen lacking a highly cellularized core, called osteoid-like matrix. The cartilage-like matrix surrounds the osteoid-like matrix. The amount of the acellular fibrous region is variable. The model organisms used in the study of cartilage in sabellid polychaetes are ''Potamilla'' species and ''[[Myxicola infundibulum]]''.<ref name="ColeHall2004" /> == Plants and fungi == [[Vascular plant]]s, particularly [[seed]]s, and the stems of some mushrooms, are sometimes called "cartilaginous", although they contain no cartilage.<ref>[http://eflora.library.usyd.edu.au/glossary/cartilaginous Eflora – Glossary]. University of Sydney (2010-06-16). Retrieved on 2015-10-26.</ref> == References == {{Reflist|30em}} == Further reading == {{refbegin}} * {{Cite book | vauthors = Keller-Peck C | year=2008 | title=Vertebrate Histology, ZOOL 400 | publisher=[[Boise State University]]}} {{refend}} == External links == * [http://www.cartilage.org Cartilage.org], International Cartilage Regeneration & Joint Preservation Society * [http://www.kumc.edu/instruction/medicine/anatomy/histoweb/cart/cart.htm KUMC.edu] {{Webarchive|url=https://web.archive.org/web/20110408221559/http://www.kumc.edu/instruction/medicine/anatomy/histoweb/cart/cart.htm |date=2011-04-08 }}, Cartilage tutorial, University of Kansas Medical Center * [http://www.bartleby.com/107/pages/page279.html Bartleby.com], text from Gray's anatomy * [http://www.madsci.org/posts/archives/Mar2003/1048719208.Dv.r.html MadSci.org], I've heard 'Ears and nose do not ever stop growing.' Is this false? * [https://web.archive.org/web/20190405021654/http://www.cartilagehealth.com/ CartilageHealth.com], Information on Articular Cartilage Injury Prevention, Repair and Rehabilitation * [http://osteoarthritis.about.com/od/osteoarthritis101/a/cartilage.htm About.com] {{Webarchive|url=https://web.archive.org/web/20110707075030/http://osteoarthritis.about.com/od/osteoarthritis101/a/cartilage.htm |date=2011-07-07 }}, Osteoarthritis * [https://archive.today/20140208190823/http://www.millerplace.k12.ny.us/webpages/lmiller/photos/636532/Cartilage%20Types.bmp Cartilage types] * [http://medical-dictionary.thefreedictionary.com/cartilage Different cartilages] on TheFreeDictionary * [http://www.histology-world.com/photoalbum/thumbnails.php?album=6 Cartilage photomicrographs] {{Bone and cartilage}} {{Authority control}} [[Category:Skeletal system]] [[Category:Connective tissue]]
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