Osteoid is the organic portion of the matrix of bone tissue. Osteoblasts begin the process of forming bone tissue by secreting the osteoid as several specific proteins. 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 twenty-five percent of bone weight. It is composed of fibers and ground substance. The predominant fiber-type is Type I collagen. The ground substance is mostly made up of chondroitin sulfate and osteocalcin.
When there is insufficient mineral or osteoblast dysfunction, the osteoid does not mineralize properly, and it accumulates. This process is called osteomalacia. Osteomalacia, when present in children, is defined as rickets.
References
Netter, Frank H. (1987), Musculoskeletal system: anatomy, physiology, and metabolic disorders. Summit, New Jersey: Ciba-Geigy Corporation
