This document discusses the histology of bone. It covers the functions of bone including support, protection, containing bone marrow, and allowing movement. It describes the specialized cells and tissues of bone, including osteoblasts that form bone, osteocytes within the bone matrix, and osteoclasts that resorb bone. The document discusses bone anatomy, the remodeling process, endochondral ossification, and features of compact bone such as osteons and canaliculi connecting osteocytes.

1. BONE
BONE
The most amazing story of bone histology!
Histology bones 1

2. Functions of Bone
1. Supports soft tissue
2. Protects vital organs (cranium, thoracic
cavity)
3. Contains bone marrow
4. Reservoir of Ca++, PO4 to maintain
constant concentrations in body fluids
5. Allows body to move
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3. Specialized CT
1. Cells
1. Osteoblasts
2. Osteocytes
3. Osteoclasts
2. Bone matrix
1. Calcified material, lacunae
3. And more….
1. Canaliculi
2. Periosteum
3. Endosteum
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4. Anatomy of a Long Bone
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5. Osteoblasts
1. Synthesize organic components of matrix
(collagen type I, proteoglycans,
glycoproteins.)
2. Collagen forms osteoids: strands of spiral
fibers that form matrix
3. Influence deposit of Ca++, PO4.
4. Active vs inactive osteoblasts
5. Estrogen, PTH stimulate activity
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6. Osteoblasts
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7. Osteocytes
1. Mature bone cells that sit in lacunae
2. Gap junctions between osteocytes provide
nutrition (15 cells in a row)
3. Maintain bony matrix; long lived cells
4. Stimulated by calcitonin; inhibited by PTH
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8. Osteocyte with Cytoplasmic
Extensions
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9. Osteocytes with Canaliculi
Photomicrograph of dried bone ground
very thin. The lacunae and canaliculi
filled with air deflect the light and
appear dark, showing the
communication between these structures
through which nutrients derived from
blood vessels flow. Medium
magnification.
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10. Osteoclasts
1. Derived from monocytes; engulf bony
material
2. Active osteoblasts stimulate osteoclast
activity
3. Large, branched, motile cells
4. Secrete enzymes that digest matrix
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11. Histology bones 11

12. Osteoclasts
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13. Bone Resorption
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14. Remodeling
On this image,
the deepest red
color is bone
while pink
represents
either
fibrocartilage
(i.e., collagen
within
cartilage) or
mineralized
cartilage. The
central clearing
represents the
invasion of bone into calcified cartilage. Osteoblasts are laying down
new bone toward the left of the upper boundary of this
cavity. osteoclasts are removing previously-formed bone .
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15. Remodeling
Remodeling
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16. Bone Replacing Cartilage
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17. Remodeling Bone
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18. Endochondral Ossification
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19. • Photomicrograph of endochondral ossification. In the upper region is a row of
osteoblasts with intense cytoplasmic basophilia, a feature to be expected in
cells synthesizing a glycoprotein (collagen). Note an osteoblast being captured
in the bone matrix (arrow). Between the layer of osteoblasts and the calcified
bone matrix is a pale region made of noncalcified bone matrix called osteoid.
PT stain. Medium magnification.
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20. Endochondral Ossification
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21. Periosteum
Mesenchyme
Fibroblasts
Osteoprogenitor
cells
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22. Histology bones 22

23. Histology bones 23

24. Histology bones 24

25. Histology bones 25

26. Osteon
1. Long cylinder parallel to long axis of
diaphysis
2. Consists of:
1. Haversian canal with nerves, blood vessels;
lamellae with osteocytes
3. Haversian canals communicate with
marrow cavity, periosteum, other canals
through Volkmann’s canals
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27. Compact Bone
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28. OSTEONS (wow!)
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29. Histology bones 29

30. Canaliculi between Osteocytes
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31. Histology bones 31