Bone provides the framework for the body, protects vital organs, and enables mechanical movement. There are two types of bones based on location - the axial skeleton which includes the skull, vertebrae, and ribs, and the appendicular skeleton which includes the bones of the upper and lower extremities. Bones can also be classified based on their shape as flat, tubular, irregular, or sesamoid bones. Microscopically, bone is made up of bone cells like osteoblasts, osteoclasts, and osteocytes as well as a matrix containing collagen, minerals, and other components. Bones receive blood supply through nutrient arteries and are innervated by nerves accompanying the blood vessels.

1. Histology of Bone

2. What is Bone:
Bone is the basic unit of skeletal system
which provides-
 Framework of the body
 Protection to vital organs
 Mechanical movement

3. Classification of Bone
Based on location: 2
Types
 Axial skeleton.
* Central axis of skeleton
* 28 skull bone
* 26 vertebrae
* 25 ribs
* 1 hyoid bone

4.  Appendicular skeleton.
* Non-axial bones of skeleton
* 64 in upper extremities
* 62 in lower extremities
Classification of Bone (cont.)

5. Based on shape:
 Flat bone: skull, vertebrae, ribs
 Tubular bone: bones in hands and feets
 Irregular bone: face and vertebral column
 Sesamoid bone: patella
 Accessory bone: bones that develop in other
ossification centre
Classification of Bone (cont.)

6. Based on size:
 Long bone: tubular in shape with a hollow
shaft.
Classification of Bone (cont.)
 Short bone: cuboidal in shape, located
in hands and feet.

7. Gross structure of bone:
 Epiphysis: Ends of a bone
 Diaphysis: Shaft of a bone
 Metaphysis: Joining of Epiphysis and
Diaphysis. This is the most vascular part of a
bone. Because most of the supplying arteries
and veins enters through this area.
 Periosteum: Outer covering of bone. This
area is pain sensitive.
 Endosteum: thin layer lining the medulary
cavity.

9. Blood and nerve supply of
Bone:
Blood: Bone has a rich vascular supply,
receiving 10-20% of total CO. major
contributing arteries are-
* Diaphyseal Nutrient artery
* Metaphyseal and Epiphysial arteries
* Periosteal arterioles
Nerves: Rich in articular extremities,
vertabrae, and flat bones. Most of the
cases nerves accompany with arteries.

10. Microscopic structure of bone:
1. Bone cell:
 Osteoprogenitor cell:
◦ Osteo = bone, pro = precursor, gen = to
produce
◦ Unspecialized cells
◦ Undergo mitosis and develop into
osteoblasts
◦ Found in: inner periosteum, endosteum,
and in canals

11.  Osteoblast:
 Cells that form bone
 Lost ability to divide
 Secretes collagen which helps build
bones
 Found on surface of bones
Microscopic structure of bone
(cont.):

12.  Osteoclast:
◦ Develop from circulating monocytes (WBC)
◦ Settles on surface of bone
◦ Function is bone resorption (destroying
matrix)
Microscopic structure of bone
(cont.):

13.  Osteocyte:
◦ Mature bone cells from osteoblasts
◦ Principal cells of bone tissue
◦ Can’t divide
◦ Maintains cellular activity
 Exchange of nutrients and waste with blood
 Calcium absorption
Microscopic structure of bone
(cont.):

14. 2. Bone matrix: Bone matrix consist of
both organic and inorganic materials.
The major constituent of matrix are-
 Type-1 collagen
 Glycos-aminoglycan
 Bi-carbonate
 Citrate
 Mg, K, P, Na
Microscopic structure of bone
(cont.):

15. 3. Haversian system: primary structural
unit of a compact bone is the
haversian system. This is usually a
few milimiteres long and 0.2mm in
diameter. This system contains-
 Haversian canal
 Volkmans canal
 blood vessel
 Bone cells
Microscopic structure of bone
(cont.):

16. Microscopic structure of bone
(cont.):

17. Microscopic structure of bone
(cont.):

18. Joints:
 Synostosis joint: Nonmovable
 Synchondrosis: joint with limited movement,
ie. Costochondral joints
 Syndesmosis: bones are joint with interrosias
membrane, ie. Tibio-fibular joint.
 Diarthrosis: joint with great mobility, ie. Knee,
shoulder etc.
Connective structure of bone:

19. Periosteum:
 Outer covering of bone
 Carries a dense network of blood, lymphatic
vessels and sensory nerve.
 Due to presence of sensory nerve
periosteum is pain sensitive.
Connective structure of bone
(cont.):

20. Endosteum:
 composed of osteoprogenitor cell
 covering of the surface of medullary cavity
and haversian canal.
Connective structure of bone
(cont.):

21. Synovium:
 Synovial membrane: smooth and
villous connective tissue.
 Consists of phagocytic and fibroblast
like cells, elastic fibers, nerve, adipose
tissue.
Meniscus
Intervertebral disc
Connective structure of bone
(cont.):