Skeleton intervertebral discs. It is not as hard and rigid as bone but is stiffer and less flexible than muscle. Cartilage is composed of specialized cells called chondrocytes that produce a large amount of extracellular matrix composed of Type II collagen (except Fibrocartilage which also contains type I collagen) fibers, abundant ground substance rich in proteoglycan, and elastin fibers. Cartilage is classified in three types, elastic cartilage, hyaline cartilage and fibrocartilage, which differ in the relative amounts of these three main components. Unlike other connective tissues, cartilage does not contain blood vessels. The chondrocytes are supplied by diffusion, helped by the
Mineralized tissues beneficial to the organism. For example, kidney stones contain mineralized tissues that are developed through pathologic processes. Hence, biomineralization is an important process to understand how these diseases occur. The evolution of mineralized tissues has been puzzling for more than a century. It has been hypothesized that the first mechanism of mammalian tissue mineralization began either in the oral skeleton of conodont or the dermal skeleton of early agnathans. The dermal skeleton is just surface dentin and basal bone, which is sometimes overlaid by enameloid. It is thought that the dermal skeleton eventually became scales, which are homologous to teeth.