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Osteoblast
 
 
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An osteoblast (from the Greek
Greek language

Greek is an Indo-European languages native to the southern Balkan peninsula, the language of the Greek people. It forms an independent branch within Indo-European....
 words for "bone
Bone

Bones are rigid organ that form part of the endoskeleton of vertebrates. They function to move, support, and protect the various organs of the body, produce red blood cell and white blood cells and store minerals....
" and "germ" or embryonic) is a mononucleate cell
Cell (biology)

The cell is the structural and functional unit of all known Life organisms. It is the smallest unit of an organism that is classified as living, and is often called the building bricks of life....
 that is responsible for bone formation. Osteoblasts produce osteoid
Osteoid

Osteoid is the organic portion of the matrix of Osseous tissue. Osteoblasts begin the process of forming bone tissue by secreting the osteoid as several specific protein....
, which is composed mainly of Type I collagen
Collagen

Collagen is the main protein of connective tissue in animals and the most abundant protein in mammals, making up about 25% to 35% of the whole-body protein content....
. Osteoblasts are also responsible for mineralization of the osteoid matrix
Extracellular matrix

In biology, the extracellular matrix is the extracellular part of animal tissue that usually provides structural support to the animal Cell in addition to performing various other important functions....
. Bone is a dynamic tissue that is constantly being reshaped by osteoblasts, which build bone, and osteoclasts, which resorb bone. Osteoblast cells tend to decrease as individuals become elderly, thus decreasing the natural renovation of the bone tissue.

oblasts arise from osteoprogenitor cells located in the periosteum
Periosteum

Periosteum is a membrane that lines the outer surface of all bone, except at the joints of long bones. Endosteum lines the inner surface of all bones....
 and the bone marrow
Bone marrow

Bone marrow is the flexible biological tissue found in the hollow interior of bones. In adults, marrow in large bones produces new blood cells....
.






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Encyclopedia


An osteoblast (from the Greek
Greek language

Greek is an Indo-European languages native to the southern Balkan peninsula, the language of the Greek people. It forms an independent branch within Indo-European....
 words for "bone
Bone

Bones are rigid organ that form part of the endoskeleton of vertebrates. They function to move, support, and protect the various organs of the body, produce red blood cell and white blood cells and store minerals....
" and "germ" or embryonic) is a mononucleate cell
Cell (biology)

The cell is the structural and functional unit of all known Life organisms. It is the smallest unit of an organism that is classified as living, and is often called the building bricks of life....
 that is responsible for bone formation. Osteoblasts produce osteoid
Osteoid

Osteoid is the organic portion of the matrix of Osseous tissue. Osteoblasts begin the process of forming bone tissue by secreting the osteoid as several specific protein....
, which is composed mainly of Type I collagen
Collagen

Collagen is the main protein of connective tissue in animals and the most abundant protein in mammals, making up about 25% to 35% of the whole-body protein content....
. Osteoblasts are also responsible for mineralization of the osteoid matrix
Extracellular matrix

In biology, the extracellular matrix is the extracellular part of animal tissue that usually provides structural support to the animal Cell in addition to performing various other important functions....
. Bone is a dynamic tissue that is constantly being reshaped by osteoblasts, which build bone, and osteoclasts, which resorb bone. Osteoblast cells tend to decrease as individuals become elderly, thus decreasing the natural renovation of the bone tissue.

Osteogenesis

Osteoblasts arise from osteoprogenitor cells located in the periosteum
Periosteum

Periosteum is a membrane that lines the outer surface of all bone, except at the joints of long bones. Endosteum lines the inner surface of all bones....
 and the bone marrow
Bone marrow

Bone marrow is the flexible biological tissue found in the hollow interior of bones. In adults, marrow in large bones produces new blood cells....
. Osteoprogenitors are immature progenitor cell
Progenitor cell

Like stem cells, progenitor cells have a capacity to differentiate into a specific type of cell. In contrast to stem cells, however, they are already far more specific: they are pushed to differentiate into their "target" cell....
s that express the master regulatory transcription factor
Transcription factor

In the field of molecular biology, a transcription factor is a protein that binds to specific DNA sequence and thereby controls the transfer of genetic information from DNA to RNA....
 Cbfa1/Runx2.

Osteoprogenitors are induced to differentiate under the influence of growth factor
Growth factor

The term growth factor refers to a naturally occurring protein capable of stimulating cellular growth, proliferation and cellular differentiation....
s, in particular the bone morphogenetic protein
Bone morphogenetic protein

Bone Morphogenetic Proteins are a group of growth factors and cytokines known for their ability to induce the formation of bone and cartilage....
s (BMPs). Aside from BMPs, other growth factors including fibroblast growth factor (FGF), platelet-derived growth factor
Platelet-derived growth factor

In molecular biology, Platelet-derived growth factor is one of the numerous growth factors, or proteins that regulate cell growth and cell division....
 (PDGF), transforming growth factor beta
Transforming growth factor

Transforming growth factor is used to describe two classes of polypeptide growth factors, TGFα and TGF beta.The name "Transforming Growth Factor" is somewhat arbitrary, since the two classes of TGFs are not structurally or genetically related to one another, and they act through different receptor mechanisms....
 (TGF-ß) may promote the division of osteoprogenitors and potentially increase osteogenesis.

Once osteoprogenitors start to differentiate into osteoblasts, they begin to express a range of genetic markers including Osterix, Col1
Collagen

Collagen is the main protein of connective tissue in animals and the most abundant protein in mammals, making up about 25% to 35% of the whole-body protein content....
, ALP
Alkaline phosphatase

Alkaline phosphatase is a hydrolase enzyme responsible for removing phosphate groups from many types of molecules, including nucleotides, proteins, and alkaloids....
, osteocalcin
Osteocalcin

Osteocalcin is a noncollagenous protein found in bone and dentin. It is secreted by osteoblasts and thought to play a role in mineralization and calcium ion homeostasis....
, osteopontin
Osteopontin

Secreted phosphoprotein 1 , also known as bone sialoprotein I , early T-lymphocyte activation , and most commonly as osteopontin , is a human gene product, which is also conserved in other species....
, and osteonectin
Osteonectin

Osteonectin is a glycoprotein in the bone that binds calcium. It is secreted by osteoblasts during bone formation, initiating mineralization and promoting mineral crystal formation....
. Although the term osteoblast implies an immature cell type, osteoblasts are in fact the mature bone cells entirely responsible for generating bone tissue in animals and humans.

Morphology and histological staining


Hematoxylin and eosin staining
H&E stain

'H&E stain', 'HE stain' or 'hematoxylin and eosin stain', is a popular staining method in histology. It is the most widely used stain in medical diagnosis; for example when a pathologist looks at a biopsy of a suspected cancer, the histological section is likely to be stained with H&E and termed H&E section, H+E section, or ...
 reveals that the cytoplasm of osteoblasts is basophilic
Basophilic

Basophilic is a technical term used by Histology. It describes the microscopic appearance of cell s and Biological tissues, as seen down the microscope, after a histological section has been stained with a basic dye....
 due to the presence of a large amount of rough endoplasmic reticulum
Endoplasmic reticulum

The endoplasmic reticulum is a eukaryote organelle that forms an interconnected network of tubules, vesicle , and cisternae within cell . The lacey membranes of the endoplasmic reticulum were first seen by Keith R....
. A large Golgi apparatus
Golgi apparatus

The Golgi apparatus is an organelle found in most eukaryote Cell . It was identified in 1898 by the Italian physician Camillo Golgi and was named after him....
 is also present in the centre. The nucleus is spherical and large. Active osteoblasts synthesize, and stain positively for, Type-I collagen
Type-I collagen

Type-I collagen is the most abundant collagen of the human body.It is present in scar tissue, the end product when tissue healing by repair....
 and alkaline phosphatase
Alkaline phosphatase

Alkaline phosphatase is a hydrolase enzyme responsible for removing phosphate groups from many types of molecules, including nucleotides, proteins, and alkaloids....
.

Osteoblasts and osteocytes


Osteoblasts that become trapped in the bone matrix become osteocyte
Osteocyte

An osteocyte, a star-shaped cell , is the most abundant cell found in compact bone. Cells contain a nucleus and a thin ring of cytoplasm. When osteoblasts become trapped in the matrix they secrete, they become osteocytes....
s. They cease to generate osteoid and mineralized matrix, and instead act in a paracrine manner on active osteoblasts. They are believed to act in a mechanosensory manner.

See also

  • Bonesetter
    Bonesetter

    A bonesetter is a practitioner of joint manipulation. Before the advent of chiropractors, osteopaths and physical therapists, bonesetters were the main providers of this type of treatment in the world....


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