histology Histology, also known as microscopic anatomy or microanatomy, is the branch of biology which studies the microscopic anatomy of biological tissues. Histology is the microscopic counterpart to gross anatomy, which looks at larger structures v ...

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

Osteoblast Osteoblasts (from the Greek language, Greek combining forms for "bone", ὀστέο-, ''osteo-'' and βλαστάνω, ''blastanō'' "germinate") are cell (biology), cells with a single Cell nucleus, nucleus that synthesize bone. However, in the p ...

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 residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...

s. When the osteoid becomes mineralized, 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 Fiber or fibre (from la, fibra, links=no) 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 incorporate ...

and

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

. The predominant type of fiber is type I

collagen Collagen () is the main structural protein in the extracellular matrix found in the body's various connective tissues. As the main component of connective tissue, it is the most abundant protein in mammals, making up from 25% to 35% of the whol ...

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 and glucuronic acid). It is usually found attached to proteins as part of a proteoglycan. A chondroitin chain can have ove ...

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 g ...

Disorders

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

rickets Rickets is a condition that results in weak or soft bones in children, and is caused by either dietary deficiency or genetic causes. Symptoms include bowed legs, stunted growth, bone pain, large forehead, and trouble sleeping. Complications ma ...

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 bon ...

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 break easily. The range of symptoms—on the skeleton as well as on the body's other organs—may be ...

, also leads to defective osteoid and brittle, fracture-prone bones. In some cases,

secondary hyperparathyroidism Secondary hyperparathyroidism is the medical condition of excessive secretion of parathyroid hormone (PTH) by the parathyroid glands in response to hypocalcemia (low blood calcium levels), with resultant hyperplasia of these glands. This diso ...

can cause 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) (or simply bone cancer) is a cancerous tumor in a bone. Specifically, it is an aggressive malignant neoplasm that arises from primitive transformed cells of mesenchymal origin (and thus a sarcoma ...

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