1. Bone Ossification 1

2. Ossification bone formation Formed by:
- mesenchyme (embryonic connective tissue)
- hyaline cartilage (supporting structures for ossification) 2

3. Composition of Human Embryonic Skeleton
fibrous connective tissue membranes
hyaline cartilage
- shaped like bones
Bone Formation Patterns
intramembranous
endochondral 3

4. Intramembranous Ossification (cont.)
bone formed within a fibrous membrane
Examples:
- broad flat bones of the skull
- mandible
- clavicles 4

5. Intramembranous Ossification (cont.)
mesenchymal cells congregate at site of future bone
- become vascularized
- cluster together
- differentiate first into osteoprogenitor cells
- differentiate into osteoblasts
center of ossification 5

6. Intramembranous Ossification (cont.)
osteoblasts secrete organic matrix of bone
once completely surrounded, osteoblasts cease to form matrix (cells now osteocytes)
osteocytes lie in lacunae with canaliculi radiating out in all directions
calcium and other minerals are deposited and tissue calcifies 6

7. Trabeculae develops as bone matrix forms
trabeculae fuse together to create the lattice-like characteristic of spongy bone
- spaces between trabeculae; filled with
vascularized connective tissue which differentiates into red bone marrow 7

8. Periosteum membrane that covers bone
consists of connective tissue, osteoprogenitor cells and osteoblasts
essential for bone growth, repair, and nutrition
develops from vascularized mesenchyme
surface layers of spongy bone are replaced by compact bone 8

9. Endochondral Ossification
replacement of cartilage by bone
most bones formed this way
Steps:
- development of cartilage model
- growth of cartilage model
- development of primary ossification center
- development of diaphysis and epiphysis 9

10. Development of Cartilage Model
mesenchymal cells congregate together in shape of future bone
mesenchymal cells differentiate into chondroblasts
chondroblasts produce cartilage matrix of hyaline cartilage
perichondrium membrane develops around model forming periosteal bone collar 10

11. Growth of Cartilage Model
Cartilage model grows in length by:
- cell division
- continued secretion of cartilage matrix
- interstitial growth (growth from
within)
Growth in thickness by:
- addition of matrix on periphery (appositional growth) 11

12. Growth of Cartilage Model (cont.)
chondrocytes in mid region of model increase in size and burst
pH change stimulates calcification of cartilage 12

13. Development of Primary Ossification Center
blood capillaries penetrate calcified cartilage
- carry bone marrow stem cells and osteoprogenitor cells into spaces
stem cells - form red bone marrow
osteoprogenitor cells - differentiate into osteoblasts (secrete matrix)
Together they produce periosteal bud 13

14. Periosteal Bud Consists of: - capillaries of periosteum
- red marrow cells
- osteoblasts
- osteoclasts 14

15. Development of Diaphysis and Epiphysis
diaphysis is replaced by compact bone
central part contains red marrow
when blood vessels enter epiphyses, secondary ossification centers develop
growth is radial
spongy bone occupies the epiphyses 15