Osteoblasts

Osteoblast
Osteoblasts (blue) rimming a bony spicule (pink - on diagonal of image). In this routinely fixed and decalcified (bone mineral removed) tissue, the osteoblasts have retracted and are separated from each other and from their underlying matrix. In living bone, the cells are linked by tight junctions and gap junctions, and integrated with underlying osteocytes and matrix H&E stain.
Details
Identifiers
Greek	osteoblast
Code	TH H2.00.03.7.00002
Anatomical terminology []

Osteoblasts (from the Greek combining forms for "bone", ὀστέο-, osteo- and βλαστάνω, blastanō "germinate") are cells with a single nucleus that synthesize bone. However, in the process of bone formation, osteoblasts function in groups of connected cells. Individual cells cannot make bone. A group of organized osteoblasts together with the bone made by a unit of cells is usually called the osteon.

Osteoblasts are specialized, terminally differentiated products of mesenchymal stem cells. They synthesize dense, crosslinked collagen and specialized proteins in much smaller quantities, including osteocalcin and osteopontin, which compose the organic matrix of bone.

In organized groups of connected cells, osteoblasts produce hydroxyapatite that is deposited, in a highly regulated manner, into the organic matrix forming a strong and dense mineralized tissue - the mineralized matrix. The mineralized skeleton is the main support for the bodies of air breathing vertebrates. It is an important store of minerals for physiological homeostasis including both acid-base balance and calcium or phosphate maintenance.

The skeleton is a large organ that is formed and degraded throughout life in the air-breathing vertebrates. The skeleton is important both as a supporting structure and for maintenance of calcium, phosphate, and acid-base status in the whole organism. The functional part of bone, the bone matrix, is entirely extracellular. The bone matrix consists of protein and mineral. The protein forms the organic matrix. It is synthesized and then the mineral is added. The vast majority of the organic matrix is collagen, which provides tensile strength. The matrix is mineralized by deposition of hydroxyapatite (alternative name, hydroxylapatite). This mineral is hard, and provides compressive strength. Thus, the collagen and mineral together are a composite material with excellent tensile and compressive strength, which can bend under a strain and recover its shape without damage. This is called elastic deformation. Forces that exceed the capacity of bone to behave elastically may cause failure, typically bone fractures.