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| Osteoid | |
|---|---|
 | |
| Identifiers | |
| FMA | 66830 |
| Anatomical terminology | |
Inhistology,osteoid is the unmineralized, organic portion of the bone matrix that forms prior to the maturation ofbone tissue.[1]Osteoblasts begin the process of forming bone tissue by secreting the osteoid as several specificproteins. The osteoid and its adjacentbone cells have developed into new bone tissue when it becomesmineralized.
Osteoid makes up about fifty percent of bone volume and forty percent of bone weight. It is composed offibers andground substance. The predominant type of fiber is type Icollagen and comprises ninety percent of the osteoid. The ground substance is mostly made up ofchondroitin sulfate andosteocalcin.
When there are insufficient nutrient minerals or osteoblast dysfunction, the osteoid does not mineralize properly and accumulates. The resultant disorder is termedrickets in children andosteomalacia in adults. A deficiency of type I collagen, such as inosteogenesis imperfecta, 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 asosteosarcoma or osteogenic sarcoma. This malignancy most often develops in adolescence during periods of rapid osteoid formation (commonly referred to as growth spurts).[2]
