1. MT: Skeletal System
I will describe the microscopic structure of compact and cancellous “spongy” bone

2. Cell that destroys bone
Bone Cells
Osteoblast
Cell that builds bone
Osteoclast
Cell that destroys bone

3. 1. Compact Bone 2. Cancellous “Spongy” Bone
Two Kinds of Bone
1. Compact Bone
2. Cancellous “Spongy” Bone

4. Compact Bone
Compact bone is arranged in units called osteons AKA Haversian systems.
Osteons are aligned in the same direction along lines of stress. These lines can slowly change as the stresses on the bone changes.

5. Histology of Bone Tissue

6. Parts of an Osteon concentric, cylindrical layers of calcified matrix
Lamellae:
Lacunae:
space where osteocytes are located
Canalculi:
ultra small canals branching off of lacunae, eventually connecting to Haversian Canals
center canal of each osteon; contains blood vessels and nerves; how nutrients are given to bone
Haversian
Canals:
Volkmann’s Canals
transverse canals that connect to Haversian Canals

7. Compact Bone
Osteon is concentric rings (lamellae) of calcified matrix surrounding a vertically oriented blood vessel

8. Compact Bone

11. Cancellous “Spongy” Bone
Latticework of thin plates of bone called trabeculae oriented along lines of stress
Spaces in between these struts are filled with red marrow where blood cells develop
Found in ends of long bones and inside flat bones such as the hipbones, sternum, sides of skull, and ribs.
No true Osteons.

13. Spongy Bone
Spongy (cancellous) bone does not contain osteons. It consists of trabeculae surrounding many red marrow filled spaces.
Spongy bone tissue is light and supports and protects the red bone marrow.

14. Just for fun...look at the following x-rays

15. Steps in Fracture Repair
1. Formation of a fracture hematoma
Immediately after the fracture, there is
a sharp fracture line with associated
soft tissue swelling. At the fracture
Site, there is abundant hematoma
with beginning fibroblastic penetration.

16. Steps in Fracture Repair
Fibrocartilaginous Callus
Formation
At 2 weeks there is much visible callus.
There is also bone resorption and
osteoporosis, both difficult to see in
this case because of the overlying callus.
There has been migration of chondroblasts
into the area and cartilage is beginning
to cover the ends of the fracture. New
osteous tissue is produced
enchondrally.

17. Steps in Fracture Repair
3. Bony Callus Formation
At 2 months, bony callus with sharp margins bridges the fracture and the fracture line itself begins to disappear.

18. Steps in Fracture Repair
4. Bone Remodeling
At 5-6 months, the marrow cavity
is continuous and the compact bone
of the diaphysis has been reformed.