Cartilage is a type of smooth, elastic tissue that provides structural support to the body e.g. joints, between bones, ears, nose, trachea, ribs and others. It consists of special cells called chondrocytes whose job it is to produce a large amount of extracellular matrix, the material between cells, which gives cartilage its physical properties.
Primarily, these components are collagen and proteolgycans, both proteins. Depending on location, cartilage can have different ratios of collagen to proteoglycans. This forms three categories of cartilage: hyaline cartilage, yellow elastic cartilage and white fibrous cartilage.
The density of chondrocytes versus extracellular matrix (ECM) can also be observed as different between elastic, fibrous and hyaline cartilage types. A lacuna is the space surrounding a cell or more cells undergoing division. Cartilage doesn’t have a blood supply or nervous tissue, so it obtains its nutrients through diffusion. Chondrocytes are relatively immobile in their ECM, so any damage sustained to cartilage would not heal the way other tissues heal, if at all.
The three different types of cartilage have different physical properties due to the density of cells to ECM. As the name indicates, yellow elastic cartilage is elastic (contains more elastic fibres) e.g. ear flaps, while white fibrous cartilage has the most ECM and is found in the spine and menisci (cartilage structures protecting against friction in knees, wrists and others). Finally, hyaline cartilage has a cell-ECM ratio between elastic and fibrous cartilage, and is found in the trachea, era, nose and elsewhere.
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