Cartilage is a resilient and smooth elastic tissue, rubber-like padding that covers and protects the ends of long bones at the joints, and is a structural component of the rib cage, the ear, the nose, the bronchial tubes, the intervertebral discs, and many more other body components. It is not as hard and rigid as bone, but it is stiffer and less flexible than muscle. Because of its rigidity, cartilage often serves the purpose of holding tubes open in the body. Examples include the rings of the trachea, such as the cricoid cartilage and carina, the torus tubarius at the opening of the pharyngotympanic/auditory tube, the ala of the nostrils, and the auricle/pinna of the ear. 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 is classified in three types, elastic cartilage, hyaline cartilage and fibrocartilage, which differ in relative amounts of collagen and proteoglycan. Cartilage does not contain blood vessels (it is avascular) or nerves (it is aneural). Nutrition is supplied to the chondrocytes by diffusion. The compression of the articular cartilage or flexion of the elastic cartilage generates fluid flow, which assists diffusion of nutrients to the chondrocytes. Compared to other connective tissues, cartilage has a very slow turnover of its extracellular matrix and does not repair.

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