Biology Forums - Study Force

I noticed that the medullary cavity is formed during endochondral ossification; however, this is not the case in intramembranous ossification.


Is this because the intramembranous ossification occurs at an early stage, before endochondral ossification begins?
Does the intramembranous ossification just start off making a couple of bone structures, afterwhich the endochondral ossification takes over, using osteoclasts to form the medullary cavity?


I hope I'm making my point clear :) Thanks, I'd really appreciate someone's input on this.

Your first statement is absolutely correct...

Osteoblasts, differentiated from the osteoprogenitor cells that entered the cavity via the periosteal bud, use the calcified matrix to secrete osteoid, which forms the bone trabecula. Osteoclasts, formed from macrophages, break down spongy bone to form the medullary (bone marrow) cavity. This makes sense because the medullary cavity has walls composed of spongy bone and is lined with a thin, vascular membrane (endosteum).

The difference between endochondral ossification and intramembranous ossification is that the bones formed by Intramembranous ossification don't form a cavity. Bones derived from endochondral ossification do. In endochondral ossification, you have cartilage replaced by bone. This process is involved in growth in length of long bones (which have cavities). Intramembranous ossification forms FLAT BONES and does not require cartilige to produce the bones it does, such as the skull, sternum, mandible, and clavicle.

Hope this clears things up :)

OH, right! That does make absolute sense.
I didn't quite realize that intramembranous ossification in the embryo was directed towards flat bones.
I read that endochondral ossification lead to the formation of long bones, I just didn't connect the dots :).
Thank you very much ^-^

np good luck