Flashcards
CARTILAGE
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- 1Cartilage possesses cells called chondrocytes, which occupy small cavities called lacunae within the extracellular matrix they secreted.The substance of cartilage is neither vascularized nor supplied with nerves or lymphatic vessels; however, the cells receive their nourishment from blood vessels of surrounding connective tissues by diffusion through the matrix.
- 2The perichondrium is a connective tissue sheath covering that overlies most cartilage. It has an outer fibrous layer and inner cellular layer whose cells secrete cartilage matrix.In areas where the cartilage has no perichondrium (e.g., the articular surfaces of the bones forming a joint), the cartilage cells receive their nourishment from the synovial fluid
- 3In the region where cartilage is to form, individual mesenchymal cells retract their processes, round up, and congregate in dense masses called chondrification centers. These cells differentiate into chondroblasts and commence secreting the typical cartilage matrix around themselves. entrapped in their own matrix ( in lacunae )Chondroblasts that are surrounded by this matrix are referred to as chondrocytes.These cells are still capable of cell division, forming a cluster of two to four or more cells in a lacuna.
These groups are known as isogenous groups and represent one, two, or more cell divisions from an original chondrocyte. As the cells of an isogenous group manufacture matrix, they are pushed away from each other, forming separate lacunae and thus enlarging the cartilage from within. This type of growth is called interstitial growth - 4Mesenchymal cells at the periphery of the developing cartilage differentiate to form fibroblasts. These cells manufacture a dense irregular collagenous connective tissue, the perichondrium, responsible for the growth and maintenance of the cartilage.The perichondrium has two layers, an outer fibrous layer composed of type I collagen, fibroblasts, and blood vessels and an inner cellular layer composed mostly of chondrogenic cells.
The chondrogenic cells undergo division and differentiate into chondroblasts, which begin to elaborate matrix. In this way cartilage also grows by adding to its periphery, a process called appositional growth. - 5Interstitial growth occurs only in the early phase of hyaline cartilage formation.Articular cartilage lacks a perichondrium and increases in size only by interstitial growth. This type of growth also occurs in the epiphyseal plates of long bones, where the lacunae are arranged in a longitudinal orientation parallel to the long axis of the bone; therefore, interstitial growth serves to lengthen the bone.
The cartilage in the remainder of the body grows mostly by apposition, a controlled process that may continue during the life of the cartilage - 6Chondrogenic cells can differentiate into both chondroblasts and osteoprogenitor cells.Chondroblasts are derived from two sources: mesenchymal cells located within the center of chondrification and chondrogenic cells of the inner cellular layer of the perichondrium (as in appositional growth). Chondroblasts are , basophilic cells that display the organelles required for protein synthesis.
- 7The matrix of hyaline cartilage contains primarily type II collagen, but types IX, X, and XI and other minor collagens are also present in small quantities.The matrix is subdivided into two regions: the territorial matrix, around each lacuna, and the interterritorial matrix. The territorial matrix, a 50-μm-wide band, is poor in collagen and rich in chondroitin sulfate, which contributes to its basophilic and intense staining with periodic acid-Schiff (PAS) reagent. The bulk of the matrix is interterritorial matrix, which is richer in type II collagen and poorer in proteoglycans than the territorial matrix.
- 8The abundant negative charges associated with these exceedingly large proteoglycan molecules attract cations, predominantly Na+ ions, which in turn attract water molecules. In this way, the cartilage matrix becomes hydrated to such an extent that up to 80% of the wet weight of cartilage is waterChondronectin thus assists these cells in maintaining their contact with the fibrous and amorphous components of the matrix.
- 9Hyaline cartilage degenerates when the chondrocytes hypertrophy and die and the matrix begins to calcify.Cartilage regeneration is usually poor except in children. Chondrogenic cells from the perichondrium enter the defect and form new cartilage. If the defect is large, the cells form dense connective tissue to repair the scar
- 10Chondrocytes of fibrocartilage usually arise from fibroblasts that begin to manufacture proteoglycansA
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- Flashcards on CARTILAGE , created by ehab mahajna on 13/05/2015.
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