structure of bone

1. Histology of bone

2. Bone composition
• Made up of intercellular substance and
bone cells
1. Intercellular substance:
a)amorphous ground substance
b)fibres
2.Bone cells
 -Highly specialised connective tissue
 -Impregnated with calcium salts.

3. Macroscopic appearance of cut surfaces
•Compact bone
•Trabecular bone
•Developmental origin
•Intrmembranous
•Intra cartilaginous
•Regions of long bones
•Diaphysis
•Metaphysis
•Epiphysis
•Organisation of collagen fibres
•Woven bone
•Parallel fibred bone

4. Classification
•1..General
microstructure
•Non – lamellar
bone
•Lamellar bone
• 2..Disposition of
lamellae
•Circumferential
•Osteonic
•Interstitial

5. Components
BONE
CELLS
OSTEOP
ROGENI
TOR
CELLS
OSTEOB
LASTS
OSTEOC
YTES
BONE
LINING
CELLS
OSTEOC
LASTS
MATRIX
ORGANI
C
FIBRES GROUN
D
SUBSTA
NCE
INORGA
NIC

6. Matrix
MATRIX
WATER
10-20%
DRY WT
ORGANIC 35%
FIBRES
COLLAGEN
GROUND
SUBS
GLYCO PR
INORGANIC
65%
MINERALS
Ca, PO4,
OH, CO3

7. Types of cells
1. Osteo Progenitor cells
2. Osteocyte: Mature bone cell
3. Osteoblast: Bone-forming cells
4. Osteoclast: Bone-destroying cells

8. Osteoblasts
 Cells that form bone
 Present where active
bone formation is
going on.
 Secretes collagen
which helps build
bones
 Found on surface of
bones

9. Osteoclasts
These are multinucleated giant cell.
 Function is bone resorption (destroying
matrix)

10. Osteoclasts closer view

11. 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
• Inactive cell.

13. Osteogenic( progenitor )cells
• Stem cells of mesenchymal origin
• Proliferate and convert into osteoblast
• Resemble fibroblast in appearance
• Present over bone surfaces on periosteal and
endosteal aspects

14. Intercellular substance:
• Contains organic and inorganic substance
• 1.Organic substance:-
• Composed of protein fibers called collagen
fibers, which are embedded, in the
gelatinous ground substance
• These collagen fibers form about 90% of the
bone.
• The ground substance is formed by the
extracellular fluid & proteoglycans.

15. • 2. Inorganic substance:-
salts of calcium and magnisium are present.

16. Types of bone
•Compact bone
•Spongy bone

17. Structure of bone
• The bone is covered by a white fibrous
connective layer called PERIOSTEUM & an
inner dense fibrous membrane called
ENDOSTEUM
• The tendons from the muscles are attached
to periosteum
• The heads of the bone are covered by a
hyaline cartilage. This forms the synovial
joint with adjoining bones

18. • The longitudinal section of most of the bones
reveal 2 layers of structures namely:
• OUTER COMPACT BONE
• INNER SPONGY BONE

19. • In most of the bones, both compact & spongy forms
are present. However, the thickness of each type
varies in different regions.
• The epiphysis contains large amount of spongy
bone & outer thin compact bone.
• In diaphysis, the amount of compact bone is more &
the spongy bone is very thin

20. Parts & Structure Of Bone

21. Compact bone
• The compact or cortical bone is hard & dense
material forming about 80% of bone in the body.
• Its main functions are mechanical function & the
protection of bone marrow.
• The cavity in the compact bone is called medullary
cavity & it contains bone marrow.

22. • The Haversian systems communicate with
each other by transverse canals called
VOLKMANN’s CANAL.
..Within haversian systems, there are central
canal called haversian canal present.
• Arround the canal spirally running lamina are
present made up spirally running collagen
fibres with calcium.
• In between or on the lamina there are
present lacunae.
LACUNAE inside which the osteocytes are
trapped.
Processes of osteocytes extend into
canaliculi.

24. Structure Of Compact Bone

25. • Interstitial lamina
• Outer circumferencial lamina
• Inner circumferencial lamina

27. Haversian Canal
• A higher magnification shows the
concentric circles. After osteoclasts
remove old bone osteoblasts deposit
bone in this circular arrangement
beginning with the outer ring and working
inward.
• As the osteoblasts become trapped in
their own calcified deposits, they are
known as osteocytes.

28. •Osteon System: A central
(Haversian) canal with concentric
rings (lamellae) of bone matrix
running lengthwise. Very strong

29. • Lacunae: tiny cavities inside the lamellae
rings. This is where the osteocytes are
found
• The central canal carries blood vessels and
nerves to all areas of the bone

31. Canaliculi : tiny canals that radiate
outward from the central canals to each
lacunae space.
Volkmann’s Canals: canals that run at
right angles to the central canals and
perforate the shaft of the bone.

35. SPONGY BONE
• The spongy or trabecular or cancellous bone forms
20% of bone in the body.
• It is made up of bone spicules or trabeculae, which
are separated by spaces.
• The spongy bone is honey comb or network of flat
pieces filled with red bone marrow & yellow bone
marrow.
• No haversian system

38. Spongy
bone

41. BONE REMODELLING
In adults, the bone tissue is kept in
dynamic equilibrium by means of
remodelling.
Bone remodelling is a process that
includes bone resorption followed by
bone formation.
Bone resorption is the process that
involves the destruction of entire bone
matrix & removal of Ca.
During bone formation there is
development of new matrix that is
mineralized.

42. BONE REMODELLING
The blue arrows indicate the osteoblasts.
The yellow arrows indicate the bone matrix they’ve just
secreted

43. Osteoclasts are concerned with bone resorption
(osteoclastic activity) & osteoblasts are concerned
with bone formation (osteoblastic activity).
Usually, bone remodelling takes place in groups of
cells called the basic multicellular units.
The entire process of remodelling extends for
about 100 days in compact bone & about 200 days
in trabecular bone.

44. Significance of bone Remodelling
Following are the significance of bone remodelling:
• In children, because of bone remodelling , the
bone becomes thick & adjusts its strength in
proportion to the growth. The shape of the bone
is also realtered in relation to the growth of the
body.
• In adults, the remodelling of bone is responsible
for the maintenance of toughness of bone. This
is because of replacement of old matrix by new
matrix

45. BONE FORMATION
• The osteoblastic activity or the process of bone
formation involves the synthesis of collagen &
formation of bone matrix that is mineralized.
• Osteoblasts (which are responsible for bone
formation) synthesize & release collagen into the
shallow depression in the bone resorbing
compartment.
• The collagen fibers arrange themselves in regular
units & form the organic matrix called OSTEOID

47. applied
• Osteoid osteoma
• Osteosarcoma
• osteomyelitis

48. MINERALIZATION
The mineralization starts about 10 to
12 days after
the formation of osteoid. ….First, a
large quantity of Ca phosphate is
deposited.
Afterwards, the hydroxide & bicarbonate
ions are gradually added causing the
formation of hydroxyapatite crystals.
The process of mineralization is
accelerated by the enzymes alkaline
phosphatase secreted by osteoblasts.

49. The process also requires the availability
of adequate amount of Ca & phosphate
in the extra cellular fluid.
• The completely mineralized bone surrounds
the osteoblast. Now, the synthetic activity
of osteoblast is reduced slowly & the cell is
converted into osteocytes.
• Later, the bone is arranged in concentric
lamellae on the inner surface of the cavity.
• At the end of the formation of new bone, the
cavity is reduced to form haversian canal

50. Bone Ground Section T.S.

51. Bone Ground Section L.S.

52. Periosteum
• Outer covering
• Absent
• Articular surface
• Sesamoid bones
• Two layers
• Outer fibrous
• Inner cellular
• Sharpey’s fibres/ extrinsic fibres

54. Sharpey’s Fibres