(Formation of the skeleton)

Embryonic Skeleton made of:

1. Fibrous membranes (cranial bones & clavicles)

2. Hyaline Cartilage (all other bones)

Intra-membranous Ossification

1. Bone develops from a fibrous membrane beg. wk 8

2. Ossification centers appear in the fibrous connective tissue membrane

[mesenchymal cells cluster and differentiate into osteoblasts = ossification center]

3. Bone Matrix (osteoid)

4. Woven bone and Periosteum form

[A. Osteoid is laid between embryonic bld vessels = network of trabeculae called woven bone.  B. Vascularized mesnechyme condenses on woven bone and becomes Periosteum]

5. Lamellar bone replaces woven bone and Red marrow appears. The resulting bones are membrane bones

Endochondral Ossification

1. Bones dev. replacing Hyaline cartilage

2. begins week 9

3. Has 5 phases: 

[1. Ossification centers form 2. Cartilage in center of diaphysis calcifies and then develops cavities 3. spongy bone begins to form 4. formation of secondary osteogenic centers 5. Epiphyses ossify. when complete, hyaline cartilage remains only in epiphyseal plates and articular cartilages.]

 4. Resulting bones are cartilage or endochondral bones

Postnatal bone growth

*Involves Interstitial & Appositional Growth

I: lengthens bones; occurs at epiphyseal plates; process stops at adolescence when E-plates ossify to form E-lines.

*(nasal bones & mandible continues to grow)

A: increases diameter; Osteoblasts add bone to periosteal surface of diaphysis; Osteoclasts remove bone on surface of diaphysis

Hormonal Regulation

of bone growth

1. Growth Hormone (GH): most important during infancy & childhood

2. Thyroid hormone: ensures bone growth is proportional

3. sex hormone: (estrogen & testosterone) stimulates bone [growth spurt]; during late adolescences, estrogen induces ossification in E-plates 

Bone Remodeling

(bone homeostasis)

• protein
• Citamins C, D, A
• calcium
• phosphorous

realignment of broken bone ends;

a method for treating fractures 

*another way fractures are treated are by immobilization (cast or traction) 

1. hematoma formation (large bld clot forms)

2. fibrocartilaginous callus forms (bld clot removed by immune sys; internal/external callus forms)

3. Spongy bone forms

4. bone remodeling occurs

• condition in adults with inadequate mineralization that causes pain
• Called "rickets" for children; often bones of legs, ribs, pelvis, and skulls are deformed
• caused my Ca²⁺ Or Vitamin D deficiency

• genetic disorder
• bones break easily
• caused by production of inadequate or poor quality collagen

• Bone resorption outpaces deposition
• bones become porous & light
• fractures common in vertebrae and neck of femur
• occurs most often in postmenopausal women
• other risk factors: small body frame; lack of exercise; poor diet; smoking; diabetes

• calcium & Vitamin D supplements
• weight-bearing exercise
• HRT in post-menopausal women
• drugs: Alendronate, Raloxifene, Statins, Fluoride, Carbonation

• excessive/haphazard bone deposition and resorption
• bone is poorly mineralized
• abnormal ratio of spongy and compact bone
• bones become deformed and painful