cartilage

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A firm, resilient connective tissue of vertebrates and some invertebrates. Isolated pieces act to provide support and anchor muscles, or with bone to contribute its resilience and interstitial growth to skeletal functions. Cartilage comprises a firm extracellular matrix synthesized by large, ovoid cells (chondrocytes) located in holes called lacunae. The matrix elements are water bound by the high negative charge of extended proteoglycan (protein-polysaccharide) molecules, and a network of fine collagen fibrils. The elements furnish mechanical stability, give, and tensile strength, but allow the diffusion of nutrients and waste to keep the cells alive. See also Bone; Collagen.

Cartilage is modified in several ways. In elastic cartilage, elastic fibers in the matrix increase resilience, as in cartilages supporting the Eustachian tube, mammalian external ear, and parts of the larynx. Where cartilage joins bones tightly at certain joints with limited mobility, for example, at the pubic symphysis and between vertebrae, the matrix of fibrocartilage contains prominent collagen fibers and has less proteoglycan than the typical hyaline variety. Hyaline cartilage, named for its glassy translucence, is the major support in the airway; and throughout the embryo, pieces of it develop as a precursor to the bony skeleton, except in the face and upper skull. See also Ear (vertebrate); Larynx.

The primitive cartilaginous skeleton undergoes another modification, by locally calcifying its matrix. At sites of calcification, invading cells destroy the cartilage and mostly replace it by bone, leaving permanent hyaline cartilage only at the joint or articular surfaces, in some ribs, and, until maturity, at growth plates set back from the joints and perpendicular to the long axis of limb bones. The precarious physiological balance between chondrocytes and matrix materials in the heavily loaded articular cartilage breaks down in old age or in inflamed joints. See also Arthritis; Connective tissue; Joint (anatomy); Skeletal system.

The hard connective tissue of the body, composed mainly of collagen, together with chondromucoid (a protein combined with chondroitin sulphate) and chondroalbuminoid (a protein similar to elastin). New bone growth consists of cartilage on which calcium salts are deposited as it develops.

Cartilage is a tough, resilient material, found in various sites but especially important in large weight-bearing joints as it lines the articulating bone ends. Due to its thickness and elasticity it is thought to act as a ‘shock-absorber’, cushioning the impact of movement. In the knee there is an extra layer of cartilage separating the bone ends (meniscus), presumably because of the amount of mechanical stress this joint is subjected to. These can be torn by rotational injuries, particularly in football and rugby players, a condition commonly referred to as ‘torn cartilage’. It is sometimes possible to repair the meniscus by ‘key-hole surgery’ (arthroscopy) which avoids having to open the joint; if the damage is too great then the meniscus is removed (menisectomy), usually by arthroscopy. Wear and thinning of articular cartilage in the knee and hip is associated with the development of osteoarthritis. Unlike most tissues in the body, cartilage has no blood vessels within it (it is ‘avascular’) and relies on getting its nutrients, essential for the continued well-being of the cells within the cartilage matrix (chondrocytes), from the thin film of fluid lining the joint cavity (synovial fluid). This fluid is derived from the blood supplying the joint capsule, and its rapid turnover is important for keeping the chondrocytes supplied with oxygen and other essential substances. Cartilage is also found near the ends of long bones (epiphysis) in children, where it plays an important role in longitudinal bone growth after birth. New chondrocytes are generated, thickening the epiphysis producing lengthwise growth, whilst the cartilage matrix ‘left behind’ acquires mineral deposits and forms bone. Cartilage is also found in other sites such as the nose, ears, and larynx (externally visible as the ‘Adam's apple’ in males), where it provides lightweight support or flexibility.

— William R. Ferrell

See also bone; connective tissue; joints.

Tough and flexible connective tissue that forms the skeleton of an embryo and most of the skeleton of infants. As a child grows, much of the cartilage is converted to bone. Cartilage is characterized by rounded cartilage cells (called chondrocytes) surrounded by mucopolysaccharide matrix (chondrin), which is rich in collagen. Cartilage has no nerves or blood vessels and heals slowly when damaged. There are three main types: hyaline cartilage, fibrocartilage, and white fibrocartilage. The pieces of semi-lunar cartilage found in the knee are called menisci.

A kind of tough but elastic connective tissue that can withstand considerable pressure. It makes up portions of the skeletal system, such as the linings of the joints, where it cushions against shock. Cartilage is also found in other body structures, such as the nose and external ear.

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A specialized, gristly connective tissue present in both mature animals and embryos, providing a model in which most of the bones develop, and constituting an important part of the organism's growth mechanism; the three most important types are hyaline cartilage, elastic cartilage and fibrocartilage. Also, a general term for a mass of such tissue in a particular site in the body.

• alar c's — the cartilages of the wings of the nose.
• annular ear c. — a ring of cartilage interposed between the rolled-up auricular cartilage and the skull.
• arthrodial c., articular c. — that clothing the articular surfaces of synovial joints.
• arytenoid c's — two pyramid-shaped cartilages of the larynx.
• auricular c. — cartilage of the pinna and much of the external ear canal.
• c. canals — tunnels containing blood vessels incorporated in developing cartilage.
• connecting c. — that connecting the surfaces of an immovable joint.
• costal c. — a bar of hyaline cartilage that attaches a rib to the sternum in the case of true ribs, or to the immediately cranial rib in the case of the anterior false ribs.
• cricoid c. — a ringlike cartilage forming the caudal part of the larynx.
• diarthrodial c. — articular cartilage.
• distal phalangeal c. — the ungual cartilages of the third phalanx in the horse lie mostly against the hoof wall but can be palpated if ossified. See also sidebone.
• elastic c. — cartilage that is more opaque, flexible and elastic than hyaline cartilage, and is further distinguished by its yellow color. The ground substance is penetrated in all directions by frequently branching fibers that give all of the reactions for elastin.
• c. emboli — see fibrocartilaginous embolic myelopathy.
• ensiform c. — xiphoid process.
• fibrous c. — fibrocartilage.
• floating c. — a detached portion of semilunar cartilage in the stifle joint.
• hoof c. — see distal phalangeal cartilage (above).
• hyaline c. — flexible, somewhat elastic, semitransparent cartilage with an opalescent bluish tint, composed of a basophilic fibril-containing substance with cavities in which the chondrocytes occur.
• interarytenoid c. — an occasional cartilage located between the two arytenoid cartilages.
• nasal c. — rostral end to the internasal septum, separating the nasal cavities and anchoring the other cartilages around the nostrils.
• parapatellar c. — cartilaginous plates medial and lateral to the patella in some species, e.g. dogs.
• permanent c. — cartilage that does not normally become ossified.
• retained enchondral c. cores — occur in ulnar metaphysis and lateral femoral condyles of young, giant breed dogs. Visible radiographically as radiolucent inverted cones, extending into the metaphysis, they are often associated with growth deformities such as forelimb valgus and genu valgum.
• reticular c. — elastic cartilage.
• scapular c. — dorsal extension of the scapula in ungulates; tends to calcify with age.
• c. scissors — used for ear cropping in dogs.
• semilunar c. — one of the two intra-articular cartilages of the stifle joint.
• temporary c. — cartilage that is normally destined to be replaced by bone.
• thyroid c. — the unpaired cartilage of the larynx to which the vocal folds attach.
• tibial c. — the bed of cartilage located on the caudal surface of the intertarsal joint of birds; the tendons of the digital flexors pass through it.
• ungual c. — see distal phalangeal cartilage (above).
• vomeronasal c. — either of the two narrow strips of cartilage, one on each side, of the nasal septum supporting the vomeronasal organ.
• xiphoid c. — posterior continuation of the sternum; supports the anterior abdominal wall, especially the linea alba.
• yellow c. — elastic cartilage.

A derivative of connective tissue arising from the mesenchyme. Typical hyaline cartilage is a flexible, rather elastic material with a semitransparent, glasslike appearance. Its ground substance, or matrix, is a complex protein (chondromucoid) through which is distributed a large network of connective tissue fibers. Distributed throughout the matrix are cartilage cells that are rounded and do not have the branching characteristics of bone cells. The cells are isolated in the matrix they have secreted and normally have no blood vessels. Therefore nutrients and metabolites are exchanged with the circulation by passage through the matrix.

• Skeleton - cartilage: tough, elastic, whitish tissue that forms skeleton of embryo, most of which later turns to bone
• Tissue, Fiber, and Integumentary System - cartilage: tough, elastic, whitish tissue around bones or through muscles; embryonic skeleton that turns to bone

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Cartilage
Hyaline cartilage showing chondrocytes and organelles, lacunae and matrix

Cartilage /ˈkɑrtɨlədʒ/ is a flexible connective tissue found in many areas in the bodies of humans and other animals, including the joints between bones, the rib cage, the ear, the nose, the elbow, the knee, the ankle, the bronchial tubes and the intervertebral discs. It is not as hard and rigid as bone but is stiffer and less flexible than muscle.

Cartilage is composed of specialized cells called chondroblasts that produce a large amount of extracellular matrix composed of Type II collagen (except fibrocartilage which also contains type I collagen) fibers, abundant ground substance rich in proteoglycan, and elastin fibers. Chondroblasts that get caught in the matrix are called chondrocytes. They lie in spaces called lacunae with up to eight chondrocytes per lacuna. Cartilage is classified in three types, elastic cartilage, hyaline cartilage and fibrocartilage, which differ in the relative amounts of these three main components.

Unlike other connective tissues, cartilage does not contain blood vessels. Because of this, it heals very slowly. The chondrocytes are supplied by diffusion, helped by the pumping action generated by compression of the articular cartilage or flexion of the elastic cartilage. Thus, compared to other connective tissues, cartilage grows and repairs more slowly.

Contents 1 Growth and development 2 Imaging 3 Diseases and treatment 3.1 Repair 4 Mechanical Properties 4.1 Frictional properties 5 Cartilage in animals 5.1 Cartilaginous fish 5.2 Invertebrate cartilage 6 See also 7 References 8 External links

Growth and development

Main article: Chondrogenesis

Cartilage under a microscope

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 chondroblasts and begins secreting the molecules that form the extracellular matrix.

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.^[1] Articular cartilage function is dependent on the molecular composition of its extracellular matrix (ECM), which consists mainly of proteoglycans and collagens. Remodeling of cartilage is predominantly affected by changes and rearrangements of the collagen matrix, which responds to tensile and compressive forces experienced by the cartilage. ^[2] Cartilage growth thus refers in most circles to matrix deposition, but can include both growth and remodeling of the extracellular matrix.

Imaging

Cartilage does not absorb x-rays under normal In vivo conditions, but a dye can be injected into the synovial membrane that will cause the 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 x-ray scans, the outer soft tissue is most likely removed so the cartilage and air boundary is enough to contrast the presence of cartilage due to refraction of the x-ray.^[3]

Histological image of hyaline cartilage stained with haematoxylin & eosin, under polarized light

Diseases and treatment

Main article: Chondropathy

Several diseases can affect cartilage. Chondrodystrophies are a group of diseases characterized by disturbance of growth and subsequent ossification of cartilage. Some common diseases affecting/involving the cartilage are listed below.

• Osteoarthritis: The cartilage covering bones (articular cartilage—a subset of hyaline cartilage) is thinned, eventually completely worn out, resulting in a "bone against bone" joint, 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 (UHMWPE). Chondroitin sulfate, a monomer of the polysaccharide portion of proteoglycan, has been claimed to reduce the symptoms of osteoarthritis, possibly by increasing the synthesis of the extracellular matrix, but recent research has not produced evidence to support this claim.^[4]
• Traumatic rupture or detachment: The cartilage in the knee is frequently damaged, and can be partially repaired through knee cartilage replacement therapy
• 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 herniation 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 suffocation as the larynx loses its rigidity and collapses.

Tumors made up of cartilage tissue, either benign or 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 glands. Conversely, chondrostatin, an ingredient of cartilage, is being investigated by Washington University researchers for its potential ability to shrink breast and musculoskeletal tumors.

The matrix of cartilage acts as a barrier, preventing the entry of lymphocytes or diffusion of immunoglobulins. This property allows for the transplantation of cartilage from one individual to another without fear of tissue rejection.

Repair

Cartilage has limited repair capabilities: Because chondrocytes are bound in 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. Damaged hyaline cartilage is usually replaced by fibrocartilage scar tissue. Over the last years, surgeons and scientists have elaborated a series of cartilage repair procedures that help to postpone the need for joint replacement.

Bioengineering techniques are being developed to generate new cartilage, using a cellular "scaffolding" material and cultured cells to grow artificial cartilage.^[5]

Mechanical Properties

The mechanical properties of articular cartilage in load bearing joints such as 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 displays viscoelastic properties.^[6]

Frictional properties

Lubricin, a glycoprotein abundant in cartilage and synovial fluid is playing a major role in biolubrication and wear protection of cartilage ^[7]

Cartilage in animals

Cartilaginous fish

Cartilaginous fish (chondrichthyes) like sharks, rays and skates have a skeleton composed entirely of cartilage. Shark cartilage is a popular but unproven dietary supplement.

Invertebrate cartilage

Cartilage tissue can also be found among invertebrates such as horseshoe crabs, marine snails, and cephalopods.

See also

• Biomechanics

References

1. ^ . http://www.sciencedirect.com/science/article/pii/S1063458407001987. 
2. ^ . http://www.sciencedirect.com/science/article/pii/S0003986108001513. 
3. ^ About.com:osteoarthritis
4. ^ "Supplements for osteoarthritis 'do not work'". BBC News. 16 September 2010. http://www.bbc.co.uk/news/health-11330747. 
5. ^ International Cartilage Repair Society ICRS
6. ^ Hayes WC, Mockros LF. 1971. Viscoelastic properties of human articular cartilage. J. App. Physiology. Vol. 31, No. 4. [1]
7. ^ Rhee DK, Marcelino J, Baker MA, Gong Y, Smits P, et al. 2005. The secreted glycoprotein lubricin protects cartilage surfaces and inhibits synovial cell overgrowth. J. Clin. Investig. 115:622–31.

General references

• Keller-Peck, C. (2008). Vertebrate Histology, ZOOL 400. Boise State University. 

External links

• Cartilage.org, International Cartilage Repair Society
• KUMC.edu, Cartilage tutorial, University of Kansas Medical Center
• Bartleby.com, text from Gray's anatomy
• MadSci.org, I've heard 'Ears and nose do not ever stop growing.' Is this false?
• CartilageHealth.com, Information on Articular Cartilage Injury Prevention, Repair and Rehabilitation
• About.com, Osteoarthritis

v t e Musculoskeletal system · connective tissue: bone and cartilage (TA A02.0, TH H3.01, GA 2.86–95) Cartilage perichondrium · fibrocartilage callus · metaphysis cells (chondroblast · chondrocyte) types (hyaline · elastic · fibrous) Bone Ossification intramembranous · endochondral Cycle osteoblast · osteoid · osteocyte · osteoclast Types cancellous · cortical Regions subchondral bone · epiphysis · epiphyseal plate/metaphysis · diaphysis · Condyle · Epicondyle Structure osteon / Haversian system · Haversian canals · Volkmann's canals · connective tissue (endosteum · periosteum) · Sharpey's fibres · enthesis · lacunae · canaliculi · trabeculae · medullary cavity · bone marrow Shapes long · short · flat · irregular · sesamoid M: BON/CAR anat(c/f/k/f, u, t/p, l)/phys/devp/cell noco/cong/tumr, sysi/epon, injr proc, drug(M5)

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Common misspelling(s) of cartilage

• cartilege
• cartilidge

Dansk (Danish)
n. - brusk

Nederlands (Dutch)
kraakbeen

Français (French)
n. - cartilage

Deutsch (German)
n. - Knorpel

Ελληνική (Greek)
n. - (ανατ.) χόνδρος, (μαγειρ.) τραγανό

Italiano (Italian)
cartilagine

Português (Portuguese)
n. - cartilagem (f)

Русский (Russian)
хрящ

Español (Spanish)
n. - cartílago

Svenska (Swedish)
n. - brosk

中文（简体）(Chinese (Simplified))
软骨

中文（繁體）(Chinese (Traditional))
n. - 軟骨

한국어 (Korean)
n. - 연골

日本語 (Japanese)
n. - 軟骨

العربيه (Arabic)
‏(الاسم) غضروف‏

עברית (Hebrew)
n. - ‮סחוס, חסחוס‬