Cartilage


Cartilage
Cartilage
Hypertrophic Zone of Epiphyseal Plate.jpg
Hyaline cartilage showing chondrocytes and organelles, lacunae and matrix

Cartilage /ˈkɑrtɨlə/ 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

Growth and development

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.

Imaging

Cartilage does not absorb x-rays under normal In vivo conditions, but a dye can be injected into the synovial membrane so the x-rays will 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. [1]


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

Diseases and treatment

There are several diseases which can affect the 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 [2]
  • 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 if damaged, it 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. [3]

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

References

  1. ^ About.com:osteoarthritis
  2. ^ "Supplements for osteoarthritis 'do not work'". BBC News. 16 September 2010. http://www.bbc.co.uk/news/health-11330747. 
  3. ^ International Cartilage Repair Society ICRS
General references

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

Wikimedia Foundation. 2010.

Synonyms:

Look at other dictionaries:

  • Cartilage — observé au microscope photonique Le cartilage est un tissu conjonctif spécialisé formé par des cellules de forme arrondie, les chondrocytes, incluses dans des logettes nommées chondroplastes au sein d une matrice extracellulaire constituée de… …   Wikipédia en Français

  • CARTILAGE — Tissu de soutien d’origine mésenchymateuse dont la différenciation dépend étroitement de la mise en jeu de facteurs mécaniques (pressions et frottements), le cartilage comprend des cellules appelées chondrocytes, de forme arrondie. Leur… …   Encyclopédie Universelle

  • Cartilage — Car ti*lage, n. [L. cartilago; cf. F. cartilage.] (Anat.) A translucent, elastic tissue; gristle. [1913 Webster] Note: Cartilage contains no vessels, and consists of a homogeneous, intercellular matrix, in which there are numerous minute cavities …   The Collaborative International Dictionary of English

  • cartilage — CARTILAGE. s. m. Terme d Anatomie. C est une partie blanche, dure, élastique, polie, privée de sentiment, qui se trouve surtout aux extrémités des os. C est ce qu on appelle vulgairement le Croquant dans la viande de boucherie. Le cartilage du… …   Dictionnaire de l'Académie Française 1798

  • cartilage — early 15c., from M.Fr. cartilage, from L. cartilago (gen. cartilaginis) cartilage, gristle, possibly related to L. crates wickerwork …   Etymology dictionary

  • cartilage — [kärt′ l ij] n. [ME & OFr < L cartilago: for IE base see HURDLE] 1. tough, elastic, whitish animal tissue; gristle: the skeletons of embryos and young animals are composed largely of cartilage, most of which later turns to bone 2. a part or… …   English World dictionary

  • cartilage — CARTILAGE. s. m. Partie qui entre en la composition du corps, & qui est de nature moyenne entre le nerf & l os; comme Le cartilage du nez des oreilles …   Dictionnaire de l'Académie française

  • cartilage — Cartilage, Cartilago. Cartilagineux, Cartilaginosus …   Thresor de la langue françoyse

  • cartilage — ► NOUN ▪ firm, flexible connective tissue which covers the ends of joints and forms structures such as the larynx and the external ear. DERIVATIVES cartilaginous adjective. ORIGIN Latin cartilago …   English terms dictionary

  • cartilage — /kahr tl ij, kahrt lij/, n. Anat., Zool. 1. a firm, elastic, flexible type of connective tissue of a translucent whitish or yellowish color; gristle. 2. a part or structure composed of cartilage. [1350 1400; ME ( < MF) < L cartilago gristle] * *… …   Universalium


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