Osteoblast

Scheme of the osteoblasts and osteoclasts.

The osteoblasts (from the Greek στέον, osteon = bone and βλαστ, blastos = germ) are bone cells responsible for synthesizing the bone matrix, which is why they are involved in the development and growth of the bones. The development of osteoblasts is influenced by different factors that stimulate their formation, such as parathyroid hormone and vitamin D. They are responsible for the maintenance, growth and repair of bone.

Histological description

Active osteoblasts.

Osteoblasts are arranged at the bone-forming front, in an epithelioid layer of low cuboidal or columnar cells. The nucleus, with a single nucleolus, is highly developed, often located at the end of the cell furthest from the bone surface. They also contain a well-developed Golgi apparatus, with numerous mitochondria, with abundant rough endoplasmic reticulum that gives an intensely basophilic color to the cytoplasm.

Osteogenesis

Osteoblasts come from osteoprogenitor cells from the periosteum and in the bone marrow that are induced to differentiate through different growth factors, particularly as bone morphogenetic proteins. Osteoprogenitor cells express the Cbfa1/Runx2 factor. Once osteoprogenitors initiate differentiation, they begin to express a range of other bone components including collagen, alkaline phosphatase, osteocalcin, osteonectin, and others.

Other growth factors including fibroblast growth factor, platelet-derived growth factor, transforming growth factor β; these can promote the division of osteoprogenitors and enhance the increase in osteogenesis.

Functions

Osteoblasts are bone cells specialized in producing the particular matrix that bone has, made up of hydroxyapatite crystals, which are mainly composed of phosphate and calcium.

Osteoblasts still maintain the ability to replicate, until they are surrounded by matrix and pass into a state of maintenance thereof called osteocytes.

The osteoblast is not a precursor of the osteoclast; these depend on the phagocytomononuclear system. Its function is to hydrolyze the matrix, in normal bone growth in children, in a fracture and also to regulate the concentration of calcium and phosphates in the blood; therefore, these cells have receptors for parathormone and calcitonin, hormones secreted by the parathyroid and thyroid respectively, which antagonize each other in hydromineral balance. Osteoclasts are multinucleated cells, they have a brush border where they produce acid phosphatase to degrade the matrix.