Essays

Intramembranous ossification takes place in the connective tissue membrane and produces the flat bones of the skull, part of the clavicle, and part of the mandible. It starts around the 8th week of development and ends at about 2 years of age. Before intramembranous ossification can take place, mesenchymal cells will condense into a soft sheet of connective tissue that is permeated with blood vessels. These mesenchymal cells will differentiate into osteochondral progenitor cells, and regions of the mesenchyme become a network of sheets called trabeculae. Osteochondral progenitor cells gather on the surface of these trabeculae and differentiate into osteoblasts. The osteoblasts deposit an organic matrix called osteoid tissue. The osteoid tissue is contains collagen and carbohydrate-protein complexes such as proteoglycans, glycosaminoglycans, and glycoproteins. The osteoid tissue is similar to bone except for a lack of minerals. Calcium phosphate will be deposited into the mat...