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Cartilage |
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Cartilage is a specialised form of connective tissue consisting of cells sparingly embedded in a firm, gel-like extracellular matrix composed of proteoglycan aggregates. The tissue is avascular and do not contain any nerves. The cells, chondrocytes are clustered in cell nests or lacunae, and are nourished by diffusion.
Most of the skeleton in the developing embryo is first formed of and later replaced by bone. In the adult, the tissue is found in specific cartilage structures and as a lining of articular surfaces. Three types are distinguished on the basis of the amount of extracellular matrix and the relative abundance of collagen and elastic fibres in the matrix. |
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The matrix of hyaline cartilage has a glassy, homogeneous, amorphous appearance and is surrounded by a thin connective tissue layer, the perichondrium. The perichondrium displays an outer more fibrous layer and inner more cellular layer. The latter serves as a source of new cartilage cells.
The matrix is highly hydrated and contains about 70% water. The matrix contains collagen type II fibrils and proteoglycans. The sulfated proteoglycans display basophilic and are visible as an intensely staining region immediate around the lacunae. Chondrocytes are rich in glycogen and lipids that are lost during slide preparation and therefore they only stain slightly. Younger, active cells may display basophilic areas. |
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| Elastic cartilage is similar in appearance than hyaline cartilage, but contains in addition to collagen fibres, a preponderance of highly branched elastic fibres that gives fresh specimens a yellow appearance. The elastic fibres are usually visualized by an elastin staining method. |
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Fibrocartilage may be seen as a combination of dense connective tissue and cartilage. Fibrocartilage differs from hyaline and elastic cartilage in that they stain intensely acidophilic due to the high collagen content.
The chondrocytes may be arranged in rows parallel to the collagen bundles, distributed individually or in pairs. A perichondrium is absent in fibrocartilage. |