There are two processes that form our bones before we are born: intramembranous ossification and endochondral ossification.
Bones of the skeleton are developed in 2 ways they are as follows:
- Intramembranous ossification: Intramembranous ossification is primarily responsible for forming the bones in our skull, and bones are formed from a specific type of connective tissue, called mesenchymal connective tissue. The replacement of sheet-like connective tissue membranes with bony tissue. Bones formed in this manner are called intramembranous bones. They include certain flat bones of the skull and some of the irregular bones. The future bones are first formed as connective tissue membranes. Osteoblasts migrate to the membranes and deposit bony matrix around themselves. When the osteoblasts are surrounded by matrix they are called osteocytes.
- Endochondral ossification is the process by which the embryonic cartilaginous model of most bones contributes to the longitudinal growth and is gradually replaced by bone. Endochondral ossification involves the replacement of hyaline cartilage with bony tissue.
Bone growth happens at the ends of the bones at the growth plate. As the bones grow, cells in the growth plate first produce more cartilage to extend the bone and then osteoblasts come in and convert the cartilage to bone in the same way that they do when bones are first formed before birth. Bones can continue to grow until about the age 16 to 20 when the growth plate turns completely to the bone and no new cartilage can be added at the ends of the bones.