INTRAMEMBRANOUS OSSIFICATION (flat bones)

Question 1

Step 1) Development of the ossification center

Answer 1

Specific chemical messages cause the cells of the mesenchyme to cluster together, first into osteoprogenitor cells and then into osteoblasts. The site of such a cluster is called an ossification center.

Question 2

Step 2) Calcification

Answer 2

Secretion of extracellular matrix stops and the cells, now called osteocytes. Extracellular matrix hardens or calcifies. ( calcification)

Question 3

Step 3) Formation of Trabeculae

Answer 3

As the bone extracellular matrix forms, it develops into trabeculae that fuse with one another to form spongy bone around the network of blood vessels in the tissue. Connective tissue associated with the blood vessels in trabeculae differentiates into red bone marrow.

Question 4

Step 4) Development of the periosteum

Answer 4

The mesenchyme condenses at the periphery of the bone and develops into the periosteum. Eventually, a thin layer of compact bone replaces the surface layers of the spongy bone, but spongy bone remains in the center. Much of the newly formed bone is remodeled (destroyed and reformed) as the bone is transformed into its adult size and shape.