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1. Histology of Bone Tissue

2. Histology of Bone Tissue
• It contains an abundant extracellular matrix that
surrounds widely separated cells
• The extracellular matrix contains:
– 15 % water
– 30 % collagen fibers
– 55 % crystallized mineral salts

3. Histology of Bone Tissue
• Four types of cells are present in bone tissue:
– Osteogenic cells
– Osteoblasts
– Osteocytes
– Osteoclasts

4. Cells in Bone Tissue
Osteogenic cells
• They are bone stem cells
• The only bone cells to undergo cell division
• They form osteoblasts
• They are found in:
– Inner portion of the periosteum
– Endosteum
– Canals within bone that contain blood vessels

5. Cells in Bone Tissue
Osteoblasts
• They are bone-building cells
• Functions:
– Synthesis of collagen fibers and other organic
components needed to build ECM
– Initiating calcification
• As they surround themselves with ECM, they
become osteocytes

6. Cells in Bone Tissue
Osteocytes
• Mature bone cells
• Their function is to maintain bone tissue’s
metabolism
• Like osteoblasts, osteocytes do not undergo
cell division

7. Cells in Bone Tissue
Osteoclasts
• Huge cells derived from the fusion
of as many as 50 monocytes
• They are concentrated in the
endosteum

8. Cells in Bone Tissue
Osteoclasts
• Ruffled border:
– Deeply folded plasma membrane
– Here the cell releases powerful lysosomal enzymes
and acids that results in resorption
• Help regulate blood calcium level in response to
certain hormones
• They are also the target cells for drug therapy used to
treat osteoporosis

9. Cells in Bone Tissue
Osteoclasts
• Resorption
– Digestion of protein and mineral components of
the ECM of bone
– It is part of the normal development, growth,
maintenance, and repair of bone

10. Compact Bone Tissue
• Also referred to as cortical or dense bone
• It is a type of bone tissue observed at the surface of a
bone
• It makes up the bulk of the diaphyses of long bones
• It is porous, with an abundance of microscopic spaces
and canals
• It provides protection and support and resists the
stresses produced by weight and movement

12. Compact Bone Tissue
Osteons/haversian systems
• Repeating structural units that composes of
compact bone
• Each osteon consists of concentric lamellae
arranged around a central (haversian) canal.

13. Compact Bone Tissue
Osteons/haversian systems
• Concentric lamellae
– Circular plates of mineralized ECM of increasing
diameter
– Surrounds a small network of blood vessels,
lymphatics, and nerves located in the central canal
• Lacunae
– Small spaces between the concentric lamellae
– They contain osteocytes

14. Compact Bone Tissue
Osteons/haversian systems
• Canaliculi
– Tiny small channels radiating in all directions from
the lacunae
– They are filled with extracellular fluid
– Slender fingerlike processes of osteocytes are
inside it

15. Compact Bone Tissue
Osteons/haversian systems
• Canaliculi
– Connects lacunae with one another and with the
central canals
• Forming miniature system of interconnected canals
throughout the bone
– This system provides blood circulation to the
osteocytes

16. Compact Bone Tissue
Osteons/haversian systems
• Osteons of long bone are aligned in the
direction parallel to the length of the diaphysis
– Long bone resists bending or fracturing even when
considerable force is applied from either end

17. Compact Bone Tissue
Osteons/haversian systems
• Interstitial lamellae
– The lamellae that are contained in the areas
between neighboring osteons
– It also have lacunae with osteocytes and canaliculi
– They are fragments of older osteons that have
been partially destroyed during bone growth

18. Compact Bone Tissue
Osteons/haversian systems
• Perforating canals/Volkmann’s canals
– Transverse canals through which neuro-vasculatures
from the periosteum penetrate the compact bone
– Their neuro-vasculatures connect with those of the
medullary cavity, periosteum and central canals.

19. Compact Bone Tissue
Osteons/haversian systems
• Circumferential lamellae
– Lamellae that are arranged around the entire
outer and inner circumference of the shaft of a
long bone

20. Compact Bone Tissue
Osteons/haversian systems
• Outer circumferential lamellae
– Circumferential lamellae directly deep to the
periosteum
– They are connected to the periosteum by Sharpey’s
fibers
• Inner circumferential lamellae
– Circumferential lamellae that line the medullary cavity

21. Spongy Bone Tissue
• Also referred to as trabecular or
cancellous bone tissue
• They does not contain osteons
• It is always covered by a layer of
compact bone for protection
• It consists of trabeculae

22. Spongy Bone Tissue
• Trabeculae
– Are lamellae that are arranged in an irregular
pattern in the spongy bone
– Between them there are spaces that are filled with
red bone marrow /yellow bone marrow
– Each of them consists of concentric lamellae,
osteocytes and canaliculi

23. Spongy Bone Tissue
• Makes up the interior bone tissue of
short, flat, sesamoid and irregular
bones
• In long bones it forms
– Core of the epiphyses
– Narrow rim bordering the medullary
cavity of the diaphysis

24. Spongy Bone Tissue
• Spongy bone is different from compact bone
in two respects.
1. Spongy bone tissue is light
▪ Allows the bone to move more readily when pulled by a
skeletal muscle
2. Their trabeculae support and protect the red
bone marrow.