Bone Structure and Remodeling
- The skeleton is a large organ formed and degraded throughout life in air-breathing vertebrates.
- The bone matrix is the functional part of bone and is entirely extracellular.
- The organic matrix is mainly composed of collagen, which provides tensile strength.
- The matrix is mineralised by the deposition of hydroxyapatite, which provides compressive strength.
- The combination of collagen and mineral creates a composite material with excellent tensile and compressive strength.
- Bone is constantly reshaped by osteoblasts and osteoclasts.
- Osteoblasts produce and secrete matrix proteins and transport mineral into the matrix.
- Osteoclasts break down bone tissue.
- Bone remodeling is essential for maintaining bone health and integrity.
- Imbalance between bone formation and bone resorption can lead to conditions like osteoporosis.

Osteoblasts
- Osteoblasts are the major cellular component of bone.
- They arise from mesenchymal stem cells.
- Osteoblasts synthesize the organic matrix before mineralization.
- Active osteoblasts are cuboidal cells involved in bone synthesis.
- Inactive osteoblasts are flattened cells when bone formation is not actively occurring.
- Osteoblasts are bone-forming cells that play a crucial role in bone development and repair.
- They are derived from mesenchymal stem cells and are responsible for synthesizing and secreting the organic components of bone matrix.
- Osteoblasts produce collagen type I, which provides tensile strength to the bone.
- They also secrete osteocalcin and osteopontin, proteins that link the organic and mineral components of bone.
- Osteoblasts are connected to each other through tight junctions and gap junctions, allowing them to function as a unit.

Osteoclasts
- Osteoclasts are multinucleated cells derived from hematopoietic progenitors.
- They break down bone tissue.
- Osteoclasts, along with osteoblasts and osteocytes, form the structural components of bone.
- Mesenchymal stem cells and blood vessels are essential for osteoblast bone formation.
- Imbalance between bone formation and bone resorption can lead to osteoporosis.

Osteogenesis
- Bone can be formed through endochondral ossification or intramembranous ossification.
- Endochondral ossification is the process of forming bone from cartilage.
- Intramembranous ossification is the direct ossification of mesenchyme.
- Osteoblast differentiation involves regulatory transcription factors.
- Bone morphogenetic proteins (BMPs) play a crucial role in skeletal differentiation.

Osteocyte Feedback and Other Aspects
- Feedback from physical activity maintains bone mass.
- Feedback from osteocytes limits the size of the bone-forming unit.
- Secretion of sclerostin by osteocytes inhibits a pathway that maintains osteoblast activity.
- Osteon deactivates bone synthesis when it reaches a limiting size.
- Osteocyte feedback plays a crucial role in bone remodeling and maintaining bone homeostasis.
- Osteoblasts have specific morphology and can be identified through histological staining.
- Various techniques have been developed for the isolation of osteoblasts.
- Osteoblast dysfunction can lead to bone diseases, such as osteoporosis and osteogenesis imperfecta.
- Researchers study osteoblasts to better understand bone formation and remodeling.
- Osteoblasts are used in tissue engineering and have potential clinical applications.

Osteoblast (Wikipedia)

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 organised osteoblasts together with the bone made by a unit of cells is usually called the osteon.

Osteoblast
Osteoblasts (purple) 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.
Illustration showing a single osteoblast
Details
Location	Bone
Function	Formation of bone tissue
Identifiers
Greek	osteoblast
MeSH	D010006
TH	H2.00.03.7.00002
FMA	66780
Anatomical terms of microanatomy [edit on Wikidata]

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

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