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MeSHCartilage_header_cell_0_2_0 Cartilage_cell_0_2_1
TA98Cartilage_header_cell_0_3_0 Cartilage_cell_0_3_1
TA2Cartilage_header_cell_0_4_0 Cartilage_cell_0_4_1

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 nerves, and is a structural component of the rib cage, the ear, the nose, the bronchial tubes, the intervertebral discs, and many other body components. Cartilage_sentence_0

It is not as hard and rigid as bone, but it is much stiffer and much less flexible than muscle. Cartilage_sentence_1

The matrix of cartilage is made up of glycosaminoglycans, proteoglycans, collagen fibers and, sometimes, elastin. Cartilage_sentence_2

Because of its rigidity, cartilage often serves the purpose of holding tubes open in the body. Cartilage_sentence_3

Examples include the rings of the trachea, such as the cricoid cartilage and carina. Cartilage_sentence_4

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_sentence_5

Cartilage is classified in three types, elastic cartilage, hyaline cartilage and fibrocartilage, which differ in relative amounts of collagen and proteoglycan. Cartilage_sentence_6

Cartilage does not contain blood vessels (it is avascular) or nerves (it is aneural). Cartilage_sentence_7

Nutrition is supplied to the chondrocytes by diffusion. Cartilage_sentence_8

The compression of the articular cartilage or flexion of the elastic cartilage generates fluid flow, which assists diffusion of nutrients to the chondrocytes. Cartilage_sentence_9

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. Cartilage_sentence_10

Structure Cartilage_section_0

Development Cartilage_section_1

Main article: Chondrogenesis Cartilage_sentence_11

In embryogenesis, the skeletal system is derived from the mesoderm germ layer. Cartilage_sentence_12

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. Cartilage_sentence_13

Following the initial chondrification that occurs during embryogenesis, cartilage growth consists mostly of the maturing of immature cartilage to a more mature state. Cartilage_sentence_14

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. Cartilage_sentence_15

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. Cartilage_sentence_16

This also justifies the non-coding RNAs' contribution in various cartilage-dependent pathological conditions such as arthritis, and so on. Cartilage_sentence_17

Articular cartilage Cartilage_section_2

The articular cartilage function is dependent on the molecular composition of the extracellular matrix (ECM). Cartilage_sentence_18

The ECM consists mainly of proteoglycan and collagens. Cartilage_sentence_19

The main proteoglycan in cartilage is aggrecan, which, as its name suggests, forms large aggregates with hyaluronan. Cartilage_sentence_20

These aggregates are negatively charged and hold water in the tissue. Cartilage_sentence_21

The collagen, mostly collagen type II, constrains the proteoglycans. Cartilage_sentence_22

The ECM responds to tensile and compressive forces that are experienced by the cartilage. Cartilage_sentence_23

Cartilage growth thus refers to the matrix deposition, but can also refer to both the growth and remodeling of the extracellular matrix. Cartilage_sentence_24

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. Cartilage_sentence_25

Function Cartilage_section_3

Mechanical properties Cartilage_section_4

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. Cartilage_sentence_26

These mechanical properties include the response of cartilage in frictional, compressive, shear and tensile loading. Cartilage_sentence_27

Cartilage is resilient and displays viscoelastic properties. Cartilage_sentence_28

Frictional properties Cartilage_section_5

Lubricin, a glycoprotein abundant in cartilage and synovial fluid, plays a major role in bio-lubrication and wear protection of cartilage. Cartilage_sentence_29

Repair Cartilage_section_6

Cartilage has limited repair capabilities: Because chondrocytes are bound in lacunae, they cannot migrate to damaged areas. Cartilage_sentence_30

Therefore, cartilage damage is difficult to heal. Cartilage_sentence_31

Also, because hyaline cartilage does not have a blood supply, the deposition of new matrix is slow. Cartilage_sentence_32

Damaged hyaline cartilage is usually replaced by fibrocartilage scar tissue. Cartilage_sentence_33

Over the last years, surgeons and scientists have elaborated a series of cartilage repair procedures that help to postpone the need for joint replacement. Cartilage_sentence_34

Biological engineering techniques are being developed to generate new cartilage, using a cellular "scaffolding" material and cultured cells to grow artificial cartilage. Cartilage_sentence_35

Clinical significance Cartilage_section_7

Disease Cartilage_section_8

Main article: Chondropathy Cartilage_sentence_36

Several diseases can affect cartilage. Cartilage_sentence_37

Chondrodystrophies are a group of diseases, characterized by the disturbance of growth and subsequent ossification of cartilage. Cartilage_sentence_38

Some common diseases that affect the cartilage are listed below. Cartilage_sentence_39


  • 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 (UHMWPE). 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.Cartilage_item_0_0
  • 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.Cartilage_item_0_1
  • Achondroplasia: Reduced proliferation of chondrocytes in the epiphyseal plate of long bones during infancy and childhood, resulting in dwarfism.Cartilage_item_0_2
  • Costochondritis: Inflammation of cartilage in the ribs, causing chest pain.Cartilage_item_0_3
  • 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.Cartilage_item_0_4
  • Relapsing polychondritis: a destruction, probably autoimmune, of cartilage, especially of the nose and ears, causing disfiguration. Death occurs by asphyxiation as the larynx loses its rigidity and collapses.Cartilage_item_0_5

Tumors made up of cartilage tissue, either benign or malignant, can occur. Cartilage_sentence_40

They usually appear in bone, rarely in pre-existing cartilage. Cartilage_sentence_41

The benign tumors are called chondroma, the malignant ones chondrosarcoma. Cartilage_sentence_42

Tumors arising from other tissues may also produce a cartilage-like matrix, the best known being pleomorphic adenoma of the salivary glands. Cartilage_sentence_43

The matrix of cartilage acts as a barrier, preventing the entry of lymphocytes or diffusion of immunoglobulins. Cartilage_sentence_44

This property allows for the transplantation of cartilage from one individual to another without fear of tissue rejection. Cartilage_sentence_45

Imaging Cartilage_section_9

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. Cartilage_sentence_46

The resulting void on the radiographic film between the bone and meniscus represents the cartilage. Cartilage_sentence_47

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. Cartilage_sentence_48

Other animals Cartilage_section_10

Cartilaginous fish Cartilage_section_11

Cartilaginous fish (chondrichthyes) like sharks, rays and skates have a skeleton composed entirely of cartilage. Cartilage_sentence_49

Invertebrate cartilage Cartilage_section_12

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. Cartilage_sentence_50

Arthropods Cartilage_section_13

The most studied cartilage in arthropods is the Limulus polyphemus branchial cartilage. Cartilage_sentence_51

It is a vesicular cell-rich cartilage due to the large, spherical and vacuolated chondrocytes with no homologies in other arthropods. Cartilage_sentence_52

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. Cartilage_sentence_53

There are homologous tissues to the endosternite cartilage in other arthropods. Cartilage_sentence_54

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. Cartilage_sentence_55

The endosternite cartilage forms close to Hh-expressing ventral nerve cords and expresses ColA and SoxE, a Sox9 analog. Cartilage_sentence_56

This is also seen in gill cartilage tissue. Cartilage_sentence_57

Mollusks Cartilage_section_14

In cephalopods, the models used for the studies of cartilage are Octopus vulgaris and Sepia officinalis. Cartilage_sentence_58

The cephalopod cranial cartilage is the invertebrate cartilage that shows more resemblance to the vertebrate hyaline cartilage. Cartilage_sentence_59

The growth is thought to take place throughout the movement of cells from the periphery to the center. Cartilage_sentence_60

The chondrocytes present different morphologies related to their position in the tissue. Cartilage_sentence_61

The embryos of Sepia officinalis express ColAa, ColAb and hyaluronan in the cranial cartilages and other regions of chondrogenesis. Cartilage_sentence_62

This implies that the cartilage is fibrillar-collagen-based. Cartilage_sentence_63

The Sepia officinalis embryo expresses hh, whose presence causes ColAa and ColAb expression and is also able to maintain proliferating cells undiferentiated. Cartilage_sentence_64

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. Cartilage_sentence_65

The cartilage growth pattern is the same as in vertebrate cartilage. Cartilage_sentence_66

In gastropods, the interest lies on the odontophore, a cartilaginous structure that supports the radula. Cartilage_sentence_67

The most studied species regarding to this particular tissue is Busycotypus canaliculatus. Cartilage_sentence_68

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. Cartilage_sentence_69

The odontophore contains muscle cells along with the chondrocytes in the case of Lymnaea and other mollusks that graze vegetation. Cartilage_sentence_70

Sabellid polychaetes Cartilage_section_15

The Sabellid polychaetes, or feather duster worms, have cartilage tissue with cellular and matrix specialization supporting their tentacles. Cartilage_sentence_71

They present two distinct extracellular matrix regions. Cartilage_sentence_72

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. Cartilage_sentence_73

The cartilage-like matrix surrounds the osteoid-like matrix. Cartilage_sentence_74

The amount of the acellular fibrous region is variable. Cartilage_sentence_75

The model organisms used in the study of cartilage in sabellid polychaetes are Potamilla sp and Myxicola infundibulum. Cartilage_sentence_76

Plants and fungi Cartilage_section_16

Vascular plants, particularly seeds, and the stems of some mushrooms, are sometimes called "cartilaginous", although they contain no cartilage. Cartilage_sentence_77

Biomechanics Cartilage_section_17


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