“Cartilage”的意思、由来-开放百科全书

Cartilage is a resilient and smooth elastic tissue, a rubber-like padding that covers and protects the ends of long bones at the joints, and is a structural component of the rib cage, the ear, the nose, the bronchial tubes, the intervertebral discs, and many other body components. 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 glycosaminoglycans, proteoglycans, collagen fibers and, sometimes, elastin.

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.

Cartilage is composed of specialized cells called chondrocytes that produce a large amount of collagenous extracellular matrix, abundant ground substance that is rich in proteoglycan and elastin fibers. Cartilage is classified in three types, elastic cartilage, hyaline cartilage and fibrocartilage, which differ in relative amounts of collagen and proteoglycan.

Cartilage does not contain blood vessels (it is avascular) or nerves (it is aneural). 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 diffusion of nutrients to the chondrocytes. Compared to other connective tissues, cartilage has a very slow turnover of its extracellular matrix and does not repair.

Structure

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 (aggrecan and collagen type II) 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

The articular cartilage function is dependent on the molecular composition of the extracellular matrix (ECM). The ECM consists mainly of proteoglycan and collagens. The main proteoglycan in cartilage is aggrecan, which, as its name suggests, forms large aggregates with hyaluronan. 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.^[2] 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.

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 viscoelastic properties.^[3]

Frictional properties

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.

Clinical significance

Disease

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.

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.

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.

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 are enough to contrast the presence of cartilage due to the refraction of the x-ray.^[7]

Other animals

Cartilaginous fish

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

Invertebrate cartilage

Cartilage tissue can also be found among some arthropods such as horseshoe crabs, some mollusks such as marine snails and cephalopods, and some annelids like sabellid polychaetes.

The most studied cartilage in arthropods is the Limulus polyphemus branchial cartilage. 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 Limulus 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 mucopolysaccharides immunoreactive against chondroitin sulfate antibodies. There are homologous tissues to the endosternite cartilage in other arthropods.^[8]

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.^[9]

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 though 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.^[8]

The embryos of Sepia 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 Sepia 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 than in vertebrate cartilage.^[9]

In gastropods, the interest lies on the odontophore, a cartilaginous structure that supports the radula. The most studied species regarding to this particular tissue is Busycon canaliculatum. The odontophore is a vesicular cell rich cartilage, consisting on 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.^[8]

The Sabellid polychaetes 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 a collagen lacking 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 sp and Myxicola infundibulum.^[8]

Plants and fungi

See also

References

1. ^{{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 β-aminopropionitrile1 | journal = Osteoarthritis and Cartilage | volume = 16 | issue = 1 | pages = 1–11 | year = 2008 | pmid = 17631390 | pmc = | doi = 10.1016/j.joca.2007.05.019 }}
2. ^{{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 = 175–182 | year = 2008 | pmid = 18394422 | pmc = 2440786 | doi = 10.1016/j.abb.2008.03.012 }}
3. ^{{cite journal | vauthors = Hayes WC, Mockros LF | title = Viscoelastic properties of human articular cartilage | journal = J Appl Physiol | volume = 31 | issue = 4 | pages = 562–8 | year = 1971 | pmid = 5111002 | doi = | url = http://jap.physiology.org/content/31/4/562.full.pdf }}
4. ^{{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 | title = The secreted glycoprotein lubricin protects cartilage surfaces and inhibits synovial cell overgrowth | journal = J Clin Invest | volume = 115 | issue = 3 | pages = 622–31 | year = 2005 | pmid = 15719068 | pmc = 548698 | doi = 10.1172/JCI22263 }}
5. ^International Cartilage Repair Society ICRS
6. ^{{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}}
7. ^Osteoarthritis. Osteoarthritis.about.com. Retrieved on 2015-10-26.
8. ^¹²³{{cite journal |last=Cole |first=A. G. |last2=Hall |first2=B. K. |year=2004 |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=261–273 |doi=10.1016/j.zool.2004.05.001 }}
9. ^¹{{cite journal |last=Tarazona |first=O. A. |last2=Slota |first2=L. A. |last3=Lopez |first3=D. H. |last4=Zhang |first4=G. |last5=Cohn |first5=M. J. |display-authors=1 |year=2016 |title=The genetic program for cartilage development has deep homology within Bilateria |journal=Nature |volume=533 |issue= |pages=86–89 |doi=10.1038/nature17398 }}
10. ^Eflora – Glossary. University of Sydney (2010-06-16). Retrieved on 2015-10-26.