BIOL 1117 Lecture Notes - Lecture 15: Intramembranous Ossification, Endochondral Ossification, Hyaline Cartilage
18 Nov 2016
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Document Summary
Ossification or osteogenesis - formation of bone. In the human fetus and infant, bone develops through 2 processes: Intramembranous ossification - produce flat bones of skull and most of clavicle. These bones develop within a fibrous sheet (certain amount of connective tissue) similar to dermis of skin. Mesenchyme (develops from mesoderm)- embryonic connective tissue condenses into a layer of soft tissue with dense supply of blood capillaries. Mesenchymal cells grow and change into osteogenic cells. Sections of mesenchyme form a network of sheets or plates (aka trabeculae) Osteogenic cells gather on plates and differentiate into osteoblasts. Osteoblasts deposit soft organic matrix (osteoid tissue) = part of bone, not true bone. This soft tissue which has collagen (like bone except not hardened yet = no minerals present yet) As plates thicken, calcium phosphate is deposited in the matrix some osteoblasts are now trapped as osteocytes. Osteoblasts produce a honeycomb of bony plates. Osteoclasts resorb other plates to form a marrow cavity.
