Cartilage

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Cartilage
Hypertrophic Zone of Epiphyseal Plate.jpg
 
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Cartilage
Hypertrophic Zone of Epiphyseal Plate.jpg

Cartilage /ˈkɑrtɨlɨ/ 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 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 Chondrocytes that produce a large amount of extracellular matrix composed of collagen fibers, abundant ground substance rich in proteoglycan, and elastin fibers. Cartilage is classified in three types, elastic cartilage, hyaline cartilage and fibrocartilage, which differ in the relative amounts of these three main components.[1] Chondroblasts that get caught in the matrix are called chondrocytes. They lie in spaces called lacunae with up to eight chondrocytes per lacuna.

Unlike other connective tissues, cartilage does not contain blood vessels. 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.

Growth and development[edit]

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.[2] 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.[3] Cartilage growth thus refers in most circles to matrix deposition, but can include both growth and remodeling of the extracellular matrix.

Imaging[edit]

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.[4]

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

Diseases and treatment[edit]

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.

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.[citation needed]

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[edit]

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.[6]

Agili-C implant and solution for Cartilage regeneration. Still experimental but has shown it can regenerate true hyaline cartilage.

Mechanical Properties[edit]

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.[7]

Frictional properties[edit]

Lubricin, a glycoprotein abundant in cartilage and synovial fluid, is playing a major role in biolubrication and wear protection of cartilage.[8]

Cartilage in animals[edit]

Cartilaginous fish[edit]

Cartilaginous fish (chondrichthyes) like sharks, rays and skates have a skeleton composed entirely of cartilage.

Invertebrate cartilage[edit]

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

Cartilaginous plants[edit]

The term cartilaginous, that is resembling cartilage, may be used in the description of vascular plants, particularly seeds. [9]

See also[edit]

References[edit]

  1. ^ Pratt, Rebecca. "Supporting Tissue: Cartilage". AnatomyOne. Amirsys, Inc. Retrieved 26 October 2012. 
  2. ^ Asanbaeva, A.; Masuda, K.; Thonar, E. J.; Klisch, S. M.; Sah, R. L. (2008). "Cartilage growth and remodeling: Modulation of balance between proteoglycan and collagen network in vitro with β-aminopropionitrile1". Osteoarthritis and Cartilage 16 (1): 1–11. doi:10.1016/j.joca.2007.05.019. PMID 17631390.  edit
  3. ^ Asanbaeva, A.; Tam, J.; Schumacher, B. L.; Klisch, S. M.; Masuda, K.; Sah, R. L. (2008). "Articular cartilage tensile integrity: Modulation by matrix depletion is maturation-dependent". Archives of Biochemistry and Biophysics 474 (1): 175–182. doi:10.1016/j.abb.2008.03.012. PMC 2440786. PMID 18394422.  edit
  4. ^ About.com:osteoarthritis
  5. ^ "Supplements for osteoarthritis 'do not work'". BBC News. 16 September 2010. 
  6. ^ International Cartilage Repair Society ICRS
  7. ^ Hayes WC, Mockros LF. 1971. Viscoelastic properties of human articular cartilage. J. App. Physiology. Vol. 31, No. 4. [1]
  8. ^ 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. doi:10.1172/JCI22263. PMC 548698. PMID 15719068. 
  9. ^ University of Sydney: Eflora - Glossary
General references

External links[edit]