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

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

3. General classifications of bones
A- Anatomical classification
B-Histological classification
C-According to the technique used on
1-Decalcified bone:
2-Ground bone:

4. A- Anatomical classification
1-Long bones :
e.g. Femur ,humerus, ulna and tibia
2-Short bones:
e.g. Bones of the hand and foot
3-Flat bone:
e.g. Scapula ,sternum,skull and ribs.
4-Irregular bones :
e.g. Pelvic bone and vertebrae.

5. Classification of Bones by Shape
Figure 6.1

6. B-Histological classification
1-Compact, regular, or non-branched.
2-Cancellous, irregular, spongy and branched.

9. Basic structures of the bone
I- CONNECTIVE TISSUE COVERINGS
Such coverings are either:
-Periosteum from the external bone surface.
-Endosteum from the interior of the bone.

10. PERIOSTEUM -It consists of two main layers:
-It is a fibrous sheath that envelops the surface of the bone except the articular surfaces.
-It consists of two main layers:
1-Outer fibrous layer and is considered
the site of muscle attachment.
2-Inner osteogenic layer which contains
the bone forming cells.

11. Periosteum
Mesenchyme
Fibroblasts
Osteoprogenitor
cells

12. II- BONE CELLS - There are four types of bone cells:
1-Osteoprogenitor cell.
2-Bone immature cell (0steoblast).
3-Bone mature cell (Osteocyte)
4-Bone eating cell (Osteoclast)

13. 1-Osteoprogenitor cell.
-It is the main stem cell that gives origin to the other types of bone cells.
-It is derived from the mesenschyme and characterized by its great mitotic activity.
-Similar to the UMC
(spindle in shape,elongated nucleus and
pale basophilic cytoplasm).

14. The Histology of Compact Bone
Figure 6.3a

15. Osteogenic cells:

16. 2-Bone immature cell (0steoblast).
-Responsible for the formation of both mature bone cell and the organic components of the bone matrix (Collagen type I, Proteoglycan and glycoprotein ).
-They arise from osteogenic cells, and when imprisoned in lacunae they are called osteocytes.
-Osteoblast is situated mainly in the inner layer of the periosteum

17. -By the LM It is a branched cell with basophilic cytoplasm which contains large round nucleus.

18. Osteoblasts

19. 3-Bone mature cell (Osteocyte)
-It is the mature bone cell.
-By LM it is branched and situated inside bony cavity called Lacuna, while its processes lies inside a cylindrical bony canaliculi.
-Only one cell is located inside each lacuna, each two cells are in contact together by gap junctions.

22. Canaliculi between Osteocytes

23. 4-Bone eating cell (Osteoclast)
-Such cell is derived from the mononuclear cell Monoctye in the bone marrow.
-It is the bone eating or resorption cell and situated at bone surface.
-It is a large cell and present inside a bony cavity called Howship’s lacuna.

24. -It contains multiple nuclei which are central in postion.
-By LM
-It is characterized by being large having acidophilic cytoplasm and serrated border.
-The border facing the bone matrix is rough and contains micovilli and called Ruffled border.
-It contains multiple nuclei which are central in postion.

25. Osteoclasts

26. III- BONE MATRIX
A-Inorganic matter (65% of bone weight)
-It is formed mainly of crystals of calcium Phosphate and carbonate.
B-Organic matter (35% of bone weight)
-It is in the form of collagenous bundles type I and ground substance.
- the matrix are arranged in special patterns:
Circumferential.
Concentric.
Interstitial .

28. Types of bone
Histologically two types of bone are known; the compact and the cancellous bone. However, bone is classified anatomically into:

29. I-Compact bone
It is the solid ivory type of bone, which is formed of regularly arranged lamellae.
Sites:
1-Diaphyses of long bones.
2-Inner and outer tables of flat bones.
3-Outer covering of irregular short bones.

31. Compact Bone:

33. II-Cancellous or Spongy Bone
It is formed of irregularly shaped trabeculae and specules containing few osteocytes.
Bone marrow fills the spaces between bone trabeculae.
Sites:
1-The middle layer of flat bones
2-Ends of long bones ( epiphyses ) and short irregular bones.

34. Spongy Bone