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Chondrogenesis is the process by which cartilage is developed. Chondrogenesis_sentence_0

Cartilage in fetal development Chondrogenesis_section_0

In embryogenesis, the skeletal system is derived from the mesoderm germ layer. Chondrogenesis_sentence_1

Chondrification (also known as chondrogenesis) is the process by which cartilage is formed from condensed mesenchyme tissue, which differentiates into chondrocytes and begins secreting the molecules that form the extracellular matrix. Chondrogenesis_sentence_2

Early in fetal development, the greater part of the skeleton is cartilaginous. Chondrogenesis_sentence_3

This temporary cartilage is gradually replaced by bone (Endochondral ossification), a process that ends at puberty. Chondrogenesis_sentence_4

In contrast, the cartilage in the joints remains unossified during the whole of life and is, therefore, permanent. Chondrogenesis_sentence_5

Mineralization Chondrogenesis_section_1

Adult hyaline articular cartilage is progressively mineralized at the junction between cartilage and bone. Chondrogenesis_sentence_6

It is then termed articular calcified cartilage. Chondrogenesis_sentence_7

A mineralization front advances through the base of the hyaline articular cartilage at a rate dependent on cartilage load and shear stress. Chondrogenesis_sentence_8

Intermittent variations in the rate of advance and mineral deposition density of the mineralizing front, lead to multiple "tidemarks" in the articular calcified cartilage. Chondrogenesis_sentence_9

Adult articular calcified cartilage is penetrated by vascular buds, and new bone produced in the vascular space in a process similar to endochondral ossification at the physis. Chondrogenesis_sentence_10

A cement line demarcates articular calcified cartilage from subchondral bones. Chondrogenesis_sentence_11

Repair Chondrogenesis_section_2

Once damaged, cartilage has limited repair capabilities. Chondrogenesis_sentence_12

Because chondrocytes are bound in lacunae, they cannot migrate to damaged areas. Chondrogenesis_sentence_13

Also, because hyaline cartilage does not have a blood supply, the deposition of new matrix is slow. Chondrogenesis_sentence_14

Damaged hyaline cartilage is usually replaced by fibrocartilage scar tissue. Chondrogenesis_sentence_15

Over the last years, surgeons and scientists have elaborated a series of cartilage repair procedures that help to postpone the need for joint replacement. Chondrogenesis_sentence_16

In a 1994 trial, Swedish doctors repaired damaged knee joints by implanting cells cultured from the patient's own cartilage. Chondrogenesis_sentence_17

In 1999 US chemists created an artificial liquid cartilage for use in repairing torn tissue. Chondrogenesis_sentence_18

The cartilage is injected into a wound or damaged joint and will harden with exposure to ultraviolet light. Chondrogenesis_sentence_19

Synthetic cartilage Chondrogenesis_section_3

Researchers say their lubricating layers of "molecular brushes" can outperform nature under the highest pressures encountered within joints, with potentially important implications for joint replacement surgery. Chondrogenesis_sentence_20

Each 60-nanometre-long brush filament has a polymer backbone from which small molecular groups stick out. Chondrogenesis_sentence_21

Those synthetic groups are very similar to the lipids found in cell membranes. Chondrogenesis_sentence_22

"In a watery environment, each of these molecular groups attracts up to 25 water molecules through electrostatic forces, so the filament as a whole develops a slick watery sheath. Chondrogenesis_sentence_23

These sheathes ensure that the brushes are lubricated as they rub past each other, even when firmly pressed together to mimic the pressures at bone joints." Chondrogenesis_sentence_24

Known as double-network hydrogels, the incredible strength of these new materials was a happy surprise when first discovered by researchers at Hokkaido in 2003. Chondrogenesis_sentence_25

Most conventionally prepared hydrogels - materials that are 80 to 90 percent water held in a polymer network - easily break apart like a gelatin. Chondrogenesis_sentence_26

The Japanese team serendipitously discovered that the addition of a second polymer to the gel made them so tough that they rivaled cartilage - tissue which can withstand the abuse of hundreds of pounds of pressure. Chondrogenesis_sentence_27

Molecular level Chondrogenesis_section_4

Bone morphogenetic proteins are growth factors released during embryonic development to induce condensation and determination of cells, during chondrogenesis. Chondrogenesis_sentence_28

Noggin, a developmental protein, inhibits chondrogenesis by preventing condensation and differentiation of mesenchymal cells. Chondrogenesis_sentence_29

The molecule sonic hedgehog (Shh) modifies the activation of the L-Sox5, Sox6, Sox9 and Nkx3.2. Chondrogenesis_sentence_30

Sox9 and Nkx3.2 induce each other in a positive feedback loop where Nkx3.2 inactivates a Sox9 inhibitor. Chondrogenesis_sentence_31

This loop is supported by BMP expression. Chondrogenesis_sentence_32

The expression of Sox9 induces the expression of BMP, which causes chondrocytes to proliferate and differentiate. Chondrogenesis_sentence_33

L-Sox5 and Sox6 share this common role with Sox9. Chondrogenesis_sentence_34

L-Sox5 and Sox6 are thought to induce the activation of the Col2a1 and the Col11a2 genes, and to repress the expression of Cbfa1, a marker for late stage Chondrocytes. Chondrogenesis_sentence_35

L-Sox5 is also thought to be involved primarily in embryonic chondrogenesis, while Sox6 is thought to be involved in post-natal chondrogenesis. Chondrogenesis_sentence_36

The molecule Indian hedgehog (Ihh) is expressed by prehypertrophic chondrocytes. Chondrogenesis_sentence_37

Ihh stimulates chondrocyte proliferation and regulates chondrocyte maturation by maintaining the expression of PTHrP. Chondrogenesis_sentence_38

PTHrP acts as a patterning molecule, determining the position in which the chondrocytes initiate differentiation. Chondrogenesis_sentence_39

Sulfation Chondrogenesis_section_5

The SLC26A2 is a sulfate transporter. Chondrogenesis_sentence_40

Defects result in several forms of osteochondrodysplasia. Chondrogenesis_sentence_41

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