Ossification is the formation of bone and is a complex process that starts in the foetal stage of development. There are various types of bone that develop in different ways. However, this essay is going to focus on the main stages of ossification of long bone and will include the role of osteoblasts and osteoclasts. A foetus is initially all cartilage until calcification takes place and the cartilage is ossified. The hyaline (meaning glassy) cartilage forms the skeleton of a foetus (www.britannica.com), it is a semi transparent matrix rich in proteoglycan (protein and glucose) and collagen and elastin fibres. These are produced via secretion by chondrocyte cells. The hyaline cartilage is surrounded by a fibrous membrane called perichondrium that contains blood vessels which supplies nourishment to the cartilage. A Cartilaginous matrix is released by the chondrocytes, it is of a firm and elastic consistency, the chondrocytes divide and produce new cells that in turn construct more matrix (Workbook).
The cartilage matrix is so solid/dense that chondrocytes are unable to feed and gain nourishment because blood capillaries cannot penetrate the matrix, they rely instead on diffusion through the matrix itself for nutrition and O2. Chondrocytes are initially very small flat cells, they eventually swell and become round in shape (Workbook). Calcium phosphate in the matrix becomes a solid and therefore produces a calcified matrix that cannot be penetrated by dissolved nutrients, the chondrocyte cannot gain nutrition now through diffusion. When this happens the chondrocyte stops dividing and dies through starvation. The calcified cartilage starts breaking down and is no longer as tough enabling osteoblasts, blood and nerves to be able to penetrate the cartilage matrix (www,faculty.stcc,edu). New bone matrix that has not yet been calcified is called osteoid. During calcification, osteoblasts become surrounded by a zone of osteoid, beyond which lies calcified bone.