Cartilage is a resilient and smooth elastic tissue, a rubber-like padding that covers and forfends the terminuses of long bones at the joints, and is a structural component of the rib cage, the auditory perceiver, the nasal perceiver, the bronchial tubes, the intervertebral discs, and many other body components. It is not as hard and rigid as bone, but it is much stiffer and much less flexible than muscle. The matrix of cartilage is composed of glycosaminoglycans, proteoglycans, collagen fibers and, sometimes, elastin.Because of its rigidity, cartilage often accommodates the purport of holding tubes open in the body. Examples include the rings of the trachea, such as the cricoid cartilage and carina.Cartilage is composed of specialized cells called chondrocytes that engender a substantial magnitude of collagenous extracellular matrix, abundant ground substance that is affluent in proteoglycan and elastin fibers. Cartilage is relegated in three types, elastic cartilage, hyaline cartilage and fibrocartilage, which differ in relative quantities of collagen and proteoglycan.Cartilage does not contain blood vessels (it is avascular) or nerves (it is aneural). Pabulum is supplied to the chondrocytes by diffusion. The compression of the articular cartilage or flexion of the elastic cartilage engenders fluid flow, which avails diffusion of nutrients to the chondrocytes. Compared to other connective tissues, cartilage has a very slow turnover of its extracellular matrix and does not rehabilitate.