Bone is a specialized connective tissue composed of cells, fibers, and minerals. It forms through two processes: endochondral ossification and intramembranous ossification. Endochondral ossification involves cartilage models that are replaced by bone, forming long bones and portions of flat bones. It begins in the second month of development. Intramembranous ossification involves mesenchymal cells directly forming bone, without a cartilage intermediate, forming bones like the skull and clavicle. Bone growth is regulated by hormones like growth hormone and sex hormones. Common bone diseases include osteogenesis imperfecta and achondroplasia.

2. General overview: Bone
 Specialized connective tissue
 Components of bone:
 Cell:osteogenic
cell,osteoblast,osteocytes,osteoclast
 Fibres:collagen type –I
 Ground substanse:chondroital sulphate,keratin
sulfate and glycoprotein
 Minerals:calcium phosphate,hydroxy apatite
crystal of calcium phosphate

3. Formation of bone:
 Mesodermal in origin
 Formed by process of ossification
a. Endochondrial ossification(cartilagenous
model)
b. Intramembranous ossification(membranous
model)

4. Law of ossification:
 secondary center which appears first unites
last with diaphysis and secondary center
which appears last unites first with diaphysis
 Exception: Fibula
 Primary center forms diaphysis whereas
secondary center forms epiphysis

5. 1.Endochondrial ossification:
 Begins at second month of embryonic
development
 Hyaline cartilage is subsequently replaced by
bone
 Leads to Growth in length and width of bone
 Bones formed are known as cartilage bones
 Formation of short and long bones.

6. Steps in endochondrial
ossification:
1.cartilageneous model 2. Formation of areolae:

7. Stages of Endochondrial
ossification:
3.Calcification of matrix: 4.Formation of areolae:

8. Endochondrial
ossification:formation of bony
lamellae

9. Structural unit of bone:
Lamellae

10. Primary center of ossification:

11. Secondary center of
ossification:

12. Growth of bone in length:

13. Increase in thickness of long
bone:

14. Intramembranous ossification:
 Mesenchymal cells directly converts to
osteoblasts with capillaries in center of
ossification
 Mostly forms flat bones
 e.g: formation of mandible, maxilla, clavicle
and most of flat bones of skull
 Begins at 8th week of development

15. 1.Stages of Intramembranous
Ossification
Figure 6.7.1

16. 2.Stages of Intramembranous
Ossification
Figure 6.7.2

17. 3.Stages of Intramembranous
Ossification
Figure 6.7.3

18. 4.Stages of Intramembranous
Ossification
Figure 6.7.4

19. Hormonal regulation of bone
formation:
1) Human growth hormone:
 Bone growth before puberty
2) Sex hormones(testosterone and estrogen)
 Development of typical male and female
shaped skeleton after puberty.
3)Parathyroid hormones:release of calcitonin

20. Clinical Anatomy:
 Dyschondroplasia or enchondromatosis
 Achondroplasia
 diaphyseal aclasis
 Osteogenesis imperfecta
 Cleido-cranial dysostosis
 Fibrous dysplasia
 Osteosclerosis
 Dwarfism
 gigantism

21. REFERENCES:
 Langman’s medical embryology,9th edition
 Singh Inderbir, G.P pal, human embryology, ninth
edition,2012
 Keith L.moore, The developing human, clinically
oriented embryology,8th edition
 Krishna Garg,Indira Bahl,Mohini Kaul A text book
of histology,a colour atlas and text, 3rd edition
 Basic histology, text and atlas,11th edition,2005
 penny(2012), bone development, retrieved on 26th
April, 2014.

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