Bone develops through two main processes: endochondral and intramembranous ossification. Endochondral ossification involves the development of a cartilage model that is later replaced by bone tissue. It occurs in long bones and involves chondroblasts forming cartilage, blood vessels infiltrating and bringing osteoprogenitor cells, and the formation of primary and secondary ossification centers. Intramembranous ossification occurs in flat bones where mesenchymal cells directly develop into bone, forming woven bone that matures into lamellar bone. Bone is made up of an organic collagen matrix and inorganic hydroxyapatite, with three main cell types involved in formation and maintenance.

1. BONE
DEVELOPMENT
By: Madiha Shams
BDS 1st Year,
Dow University Of Health Sciences

2. BONE
•
Bone is specialized, mineralized connective
tissue consisting by weight of 33% organic
matrix, 28% type l collagen, and 5%
noncollagenous proteins, including
osteonectin, osteocalcin, bone morphogenitic
proteins, bone proteoglycan and bone
sialoprotein.
• This organic matrix is permeated by
hydroxypatite (Ca10 (PO4)6 (0H)2 ), which makes
up the remaining 67% of bone.

3. COMPOSTION OF BONE

4. BONE FORMING CELLS
1. OSTEOBLAST:
* Uninucleated
* Cuboidal and columnar in shape.
* Forms bone
2. OSTEOCYTES:
* Star-shaped cell
* Most abundant cell found in compact bone.
* Maintain bone (together with inactive
osteoblasts lining cells)
3. OSTEOCLAST:
* Large, Multinucleated
* Resorb bone

5. Endochondral Bone Formation
 Chondroblasts develops in primitive
Mesenchymal & form an early
Perichondrium Cartilage model.
 The developing Cartilage model
assumes the Shape of bone to be formed
and a surrounding Perichondrium
becomes identified.

6. Endochondral Bone Formation
 At the midshaft of the diaphysis
the perichondrium becomes a
periosteum through development
of Osteoprogentor cells and
Osteoblasts, producing a collar of
Bone by Intramembrane ossification
Calcium salts are deposited in
enlarging cartilage model.
 Blood vessels grow through
the periostem and bone collar carrying Osteoprogenitor cell
within them. These cells establish a primary ossification center
Diaphysis.

7. Endochondral Bone Formation
 Bony trabeculae spread out from
the primary ossification center to
occupy the entire diaphysis linking up
with previously formed bone collar
with now forms the cortical bone of
diaphysis. At this stage the terminal
Dub-shaped epiphysis are still
composed of cartilage.

8. Endochondral Bone Formation
 At both of them (the presise
time varies between long bones)
secondary or epiphysal ossification
centre are established along with blood
Vessels of mesenchymal cells which
becomes Osteoprogentor cells and
Osteoblast.

9. Endochondral Bone Formation

10. Intramembranous Bone
Formation

11. Intramembranous Bone
Formation
 COARSE WOVEN BONE:
The bone is cellular and disorganized.

12. Intramembranous Bone
Formation
 IMMATURE BONE:
The bone is less cellular and slightly more organized,
Some primary osteons are forming.

13. Intramembranous Bone
Formation
 MATURE LAMELLAR BONE:
The tightly packed osteons create an organized bone matrix;
fewer cells and little loose connective are apparent. As
remodeling of the bone in its mature state takes place, the
periosteal bone surface becomes more regular and eventually
will be covered with circumferential lamellae.