Bone Formation, Growth, and Remodeling

• What is the order of the bone healing formation?


  1.) hematoma formation

  2.) fibrocartilaginous callus formation

  3.) bony callus formation

  4.) bone remodelling

  
• Bone formation and growth

  -Ossification is the process of bone formation

  -occurs in hyaline cartilage models or fibrous membranes

  -long Bone growth involves two major phases
• Two major phases of ossification in long bones

  1. In an embryo, osteoblasts(bone forming cells) cover the hyaline cartilage model with bone matrix

  2. In a fetus, the enclosed cartilage is covered by bone; the cartilage is digested away, opening up a medullary cavity

  
• By birth, most cartilage is converted to bone except for two regions in a long bone:


  1. Articular cartilage

  2. Epiphyseal plates

  
• New cartilage is formed continuously on

  external face of these two cartilages
• Old cartilage is broken down and replaced by

  bony matrix
• appositional growth


  -Bones grow in width

  -Osteoblasts in the periosteum add bone matrix to the outside of the diaphysis

  -Osteoclasts in the endosteum remove bone from the inner surface of the diaphysis
• Bone growth is controlled by

  hormones, such as growth hormone and sex hormones
• Bones are remodeled throughout life in response to two factors:

  1. Calcium ion level in the blood determines when bone matrix is to be broken down or formed

  2. Pull of gravity and muscles on the skeleton determines where bone matrix is to be broken down or formed
• parathyroid hormone


  -Released when calcium ion levels in blood are low

  - Activates osteoclasts(bone destroying cells)

  - Osteoclasts break down bone and release calcium ions into the blood

  - Hyperclcemia(high blood calcium levels) prompts calcium storage to bones by osteoblasts