In histology
Histology is the study of the microscopic anatomy of cells and tissues of plants and animals. It is performed by examining cells and tissues commonly by sectioning and staining; followed by examination under a light microscope or electron microscope...

, osteoid is the unmineralized, organic portion of the bone matrix that forms prior to the maturation of bone tissue
Osseous tissue
Osseous tissue, or bone tissue, is the major structural and supportive connective tissue of the body. Osseous tissue forms the rigid part of the bone organs that make up the skeletal system.-Formation:Bone tissue is a mineralized connective tissue...

. Osteoblast
Osteoblasts are mononucleate cells that are responsible for bone formation; in essence, osteoblasts are specialized fibroblasts that in addition to fibroblastic products, express bone sialoprotein and osteocalcin.Osteoblasts produce a matrix of osteoid, which is composed mainly of Type I collagen...

s begin the process of forming bone tissue by secreting the osteoid as several specific protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

s. When the osteoid becomes mineralized
Mineralization (biology)
In biology, mineralization refers to the process where an organic substance is converted to an inorganic substance.This may also be a normal biological process which takes place during the life of an organism such as the formation of bone tissue or egg shells, largely with calcium.This term may...

, it and the adjacent bone cells have developed into new bone tissue.

Osteoid makes up about fifty percent of bone volume and forty percent of bone weight. It is composed of fibers
Fibrous protein
Scleroproteins, or fibrous proteins, constitute one of the three main classes of proteins, alongside globular proteins and conjugated proteins.Keratin, collagen, elastin, and fibroin are all scleroproteins...

 and ground substance
Ground substance
Ground substance is a term for the non-cellular components of extracellular matrix which contain the fibers.It is usually not visible on slides, because it is removed during the preparation process....

. The predominant fiber-type is Type I collagen
Collagen is a group of naturally occurring proteins found in animals, especially in the flesh and connective tissues of mammals. It is the main component of connective tissue, and is the most abundant protein in mammals, making up about 25% to 35% of the whole-body protein content...

 and comprises ninety percent of the osteoid. The ground substance is mostly made up of chondroitin sulfate
Chondroitin sulfate
Chondroitin sulfate is a sulfated glycosaminoglycan composed of a chain of alternating sugars . It is usually found attached to proteins as part of a proteoglycan. A chondroitin chain can have over 100 individual sugars, each of which can be sulfated in variable positions and quantities...

 and osteocalcin
Osteocalcin, also known as bone gamma-carboxyglutamic acid-containing protein , is a noncollagenous protein found in bone and dentin. In humans, the osteocalcin is encoded by the BGLAP gene.- Function :...



When there is insufficient mineral or osteoblast dysfunction, the osteoid does not mineralize properly, and it accumulates. The resultant disorder is termed rickets
Rickets is a softening of bones in children due to deficiency or impaired metabolism of vitamin D, magnesium , phosphorus or calcium, potentially leading to fractures and deformity. Rickets is among the most frequent childhood diseases in many developing countries...

 in children and osteomalacia
Osteomalacia is the softening of the bones caused by defective bone mineralization secondary to inadequate amounts of available phosphorus and calcium, or because of overactive resorption of calcium from the bone as a result of hyperparathyroidism...

 in adults.

In very rare cases, primitive transformed cells of mesenchymal origin exhibit osteoblastic differentiation and produce malignant osteoid, which results in the formation of a malignant primary bone tumor known as osteosarcoma
Osteosarcoma is an aggressive cancerous neoplasm arising from primitive transformed cells of mesenchymal origin that exhibit osteoblastic differentiation and produce malignant osteoid...

or osteogenic sarcoma. This malignancy most often develops in adolescence during periods of rapid osteoid formation (commonly referred to as growth spurts).

External links

- "Bone, femur"
The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.