* Bone formation termed ossification of calcification
* Endochondral ossification –
Forms all bones below skull (except clavicle)
New bone forms from a hyaline cartilage model
Bone tissue replaces the cartilage model
Begins in the interior of each bone from an ossification center Ossification center – group of stem cells that transform into osteoblasts Long bones – ossification centers in the diaphysis and each epiphysis Short bones – one ossification center only
Irregular bones – several ossification centers form
Hyaline cartilage remains in the:
1) articular cartilage
2) epiphyseal plate (until closure of the plate)
* Intramembranous Ossification –
Forms all bones of the skull as well as clavicle
New bone forms within a fibrous connective tissue membrane
Growth in Long Bones
* Growth in length occurs at epiphyseal plates by endochondral ossification * Growth in width occurs by appositional growth:
Osteoblasts just deep to periosteum secrete new bone
Osterclasts just below endosteum resorb bone to maintain proper thickness
* Involves two processes:
1) Bone deposition (osteoblasts secrete new bone)
2) Bone resorption (osteoclasts resorb bone)
* Control of remodeling
1) Hormonal – parathyroid hormone mostly and to some extent calcitonin regulate calcium blood levels.
Bone serves as a depot for calcium storage in the body.
Calcium is either stored in new bone or released from resorbed bone in response to blood level homeostasis needs (negative feedback)
2) Response to stresses placed on bone. (remember how trabeculae line up along lines of concentrated stress forces) In areas where bones are placed under stress the bone is reinforced by additional new bone In areas not subjected to stress bone is resorbed.
The process is described by Wolff’s Law
Wolff’s Law – bone is...