Embryonic Ossification PDF

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full descriptive process of embryonic ossification...

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Embryonic Ossification There are two types of embryonic ossification, intramembranous and endochondral ossification. Endochondral ossification is more common than intramembranous ossification.

Intramembranous ossification is when bone is created directly within a fibrous membrane. First, osteoblasts secrete osteoid, which hardens and encourages certain osteoblasts to mature into osteocytes. The osteocytes then form trabeculae, which gets wrapped by blood vessels, ultimately creating the periosteum. Finally, cortical bone begins to grow between the periosteum and trabeculae. Flat bones are primarily made through intramembranous ossification.

Endochondral ossification is when bones are created indirectly. First, a cartilage model is created at the eighth week of development. As development continues, the center of the cartilage model begins to calcify. At the twelfth week of development, capillaries and osteoblasts begin to invade the calcified center, establishing the primary ossification center. Finally, secondary ossification centers are established at the epiphyses and osteoclasts chew out the inside of the diaphysis, creating the medullary cavity. Long bones are made through endochondral ossification.c

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