|osteoblast (ŏs'tē-ə-blāst') Pronunciation Key
A specialized bone cell that produces and deposits the matrix that is needed for the development of new bone and consists primarily of collagen fibers. Osteoblasts are formed from osteoclasts on the outer surfaces of bone and in bone cavities, and bone deposition takes place constantly in living bone. As new bone grows and hardens with the addition of calcium and phosphate, osteoblasts become embedded in the bone matrix and develop into osteocytes.
large cell responsible for the synthesis and mineralization of bone during both initial bone formation and later bone remodeling. Osteoblasts form a closely packed sheet on the surface of the bone, from which cellular processes extend through the developing bone. They arise from the differentiation of osteogenic cells in the periosteum, the tissue that covers the outer surface of the bone, and in the endosteum of the marrow cavity. This cell differentiation requires a regular supply of blood, without which cartilage-forming chondroblasts, rather than osteoblasts, are formed. The osteoblasts produce many cell products, including the enzymes alkaline phosphatase and collagenase, growth factors, hormones such as osteocalcin, and collagen, part of the organic unmineralized component of the bone called osteoid. Eventually the osteoblast is surrounded by the growing bone matrix, and, as the material calcifies, the cell is trapped in a space called a lacuna. Thus entrapped, it becomes an osteocyte, or bone cell. Osteocytes communicate with each other as well as with free bone surfaces via extensive cytoplasmic processes that occupy long, meandering channels (canaliculi) through the bone matrix
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