histology Histology, also known as microscopic anatomy or microanatomy, is the branch of biology that studies the microscopic anatomy of biological tissue (biology), tissues. Histology is the microscopic counterpart to gross anatomy, which looks at large ...

, osteoid is the unmineralized, organic portion of the bone matrix that forms prior to the maturation of

bone tissue A bone is a Stiffness, rigid Organ (biology), organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red blood cell, red and white blood cells, store minerals, provi ...

Osteoblast 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 fu ...

s begin the process of forming bone tissue by secreting the osteoid as several specific

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metab ...

s. The osteoid and its adjacent bone cells have developed into new bone tissue when it becomes mineralized. Osteoid makes up about fifty percent of bone volume and forty percent of bone weight. It is composed of

fibers Fiber (spelled fibre in British English; from ) is a natural or artificial substance that is significantly longer than it is wide. Fibers are often used in the manufacture of other materials. The strongest engineering materials often inco ...

and

ground substance Ground substance is an amorphous gel-like substance in the extracellular space of animals that contains all components of the extracellular matrix (ECM) except for fibrous materials such as collagen and elastin. Ground substance is active in the d ...

. The predominant type of fiber is type I

collagen Collagen () is the main structural protein in the extracellular matrix of the connective tissues of many animals. It is the most abundant protein in mammals, making up 25% to 35% of protein content. Amino acids are bound together to form a trip ...

and comprises ninety percent of the osteoid. The ground substance is mostly made up of

chondroitin sulfate Chondroitin sulfate is a sulfated glycosaminoglycan (GAG) composed of a chain of alternating sugars (N-Acetylgalactosamine, N-acetylgalactosamine and glucuronic acid). It is usually found attached to proteins as part of a proteoglycan. A chondroit ...

and

osteocalcin Osteocalcin, also known as bone gamma-carboxyglutamic acid-containing protein (BGLAP), is a small (49-amino-acid) noncollagenous protein hormone found in bone and dentin, first identified as a calcium-binding protein. Because osteocalcin has ...

Disorders

When there are insufficient nutrient minerals or osteoblast dysfunction, the osteoid does not mineralize properly and accumulates. The resultant disorder is termed

rickets Rickets, scientific nomenclature: rachitis (from Greek , meaning 'in or of the spine'), is a condition that results in weak or soft bones in children and may have either dietary deficiency or genetic causes. Symptoms include bowed legs, stun ...

in children and

osteomalacia Osteomalacia is a disease characterized by the softening of the bones caused by impaired bone metabolism primarily due to inadequate levels of available phosphate, calcium, and vitamin D, or because of resorption of calcium. The impairment of b ...

in adults. A deficiency of type I collagen, such as in

osteogenesis imperfecta Osteogenesis imperfecta (; OI), colloquially known as brittle bone disease, is a group of genetic disorders that all result in bones that bone fracture, break easily. The range of symptoms—on the skeleton as well as on the body's other Or ...

, also leads to defective osteoid and brittle, fracture-prone bones. In some cases, secondary hyperparathyroidism can cause a disturbance in mineralisation of calcium and phosphate. Another condition is a disturbance in primitive transformed cells of mesenchymal origin, which exhibit osteoblastic differentiation and produce malignant osteoid. This results in the formation of a malignant primary bone tumor known as

osteosarcoma An osteosarcoma (OS) or osteogenic sarcoma (OGS) is a cancerous tumor in a bone. Specifically, it is an aggressive malignant neoplasm that arises from primitive transformed cells of mesenchyme, mesenchymal origin (and thus a sarcoma) and that exhi ...

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

References

* *

External links

* - "Bone, femur"
Dr. Susan Ott's website on osteomalacia
{{Bone and cartilage Proteins Bones