BONE FORMATION & REMODELLING Ossification/Bone Formation  The process by which new bone is produced There are 2 forms of ossification: 1 - Compact Bone : Compact bone begins as cartilage Osteoblasts (bone forming cells)within cartilage discharge an osteoid (gelatin-like) Osteoids contain minerals that form the hardened bone *Short bones – one ossification center in the middle *Long bones – three ossification centers (center and both ends)

2 – Cancellous Bone 2 – Cancellous Bone(ie. Flat bones): Begins as fibrous membranes Osteoblasts release osteoid into this membrane Forms a sponge-like bundle of fibres New cancellous bone formation then develops outward from these centres in the membrane “Soft-spot” –but formation of the bones of the skull is not complete at birth. Bones have not yet fused -Cranial sutures in the adult skull are sites where the bones have formed together

Bone Remodelling  Bones cannot grow by cell division, but they can “remodel” 2 main phases… 1)Osteoclasts remove old bone by release of acid and enzymes. 2)Osteoblasts secretes protein which deposits to form new tissue

Epiphyseal Plates: Also known as “growth plates” Exist at various places on the epiphyses of long bones X-ray  black spaces appearing between the epiphyses and diaphysis is an indicator that linear growth is still possible

Epiphyseal Lines Epiphyseal plates that have fused together Indicates that linear growth is no longer possible X-ray  no black space is seen, instead a solid epiphysis is evident