1. Microscopic Structure of Bone

2. STRUCTURE A. COMPACT BONE
-coats all bones, especially present in the diaphysis of long bones
-strong, weight-bearing, stress-resisting bone with few spaces
-dynamic (change in response to demand)

4. STRUCTURE
A. COMPACT BONE – strong, weight-bearing, stress-resisting bone with few spaces
1. OSTEON “HAVERSIAN SYSTEM”– repeating unit, run length of shaft

5. STRUCTURE
COMPACT BONE – strong, weight-bearing, stress-resisting bone with few spaces
2. HAVERSIAN (CENTRAL) CANALS – present in each osteon; lengthwise canals supplying nerves & vascular tissue

6. STRUCTURE
COMPACT BONE – strong, weight-bearing, stress-resisting bone with few spaces
3. LAMELLAE – rings of hard calcified matrix surrounding haversion canals

7. STRUCTURE
COMPACT BONE – strong, weight-bearing, stress-resisting bone with few spaces
4. PERFORATING (VOLKMANN’S) CANALS – cross-sectional canals supplying nerves & blood vessels; connect w/ blood vessels of periosteum, central canal & marrow cavity

8. STRUCTURE
COMPACT BONE – strong, weight-bearing, stress-resisting bone with few spaces
5. LACUNAE – small openings containing osteocytes -between lamellae

9. STRUCTURE
COMPACT BONE – strong, weight-bearing, stress-resisting bone with few spaces
6. CANALICULI – (“tiny canals”) containing osteocyte extensions and fluids connecting both lacunae and haversion canals together (creates branching network for transportation of nutrients and wastes) osteocytes communicate with one another

10. B. SPONGY BONE
irregular latticework of branches, trabeculae (“little beams”; found where bone not heavily stressed but precisely oriented along lines of stress coming from many directions)

11. B. SPONGY BONE
many spaces containing red marrow (blood cell production)
light wt.; found in flat bones, the ends of long bones, and short and irregular bones

12. Red vs. Yellow Marrow
In children red marrow fills most marrow cavities
In adults:
most of red marrow turns to fatty yellow marrow
Red marrow limited to skull, vertebrae, ribs sternum, part of hip and proximal heads of humerus and femur
In event of severe or chronic anemia or blood loss, yellow marrow can transform back into red

13. STRUCTURE

14. STRUCTURE

15. STRUCTURE A. D. E. B. F. D. F. C. B. A. COMPACT BONE
1. OSTEON “HAVERSION SYSTEM”
2. HAVERSION (CENTRAL) CANALS
3. LAMELLAE
4. PERFORATING (VOLKMANN’S) CANALS
5. LACUNAE
6. CANILICULI D. E. B. F. D. F. C. B.

16. Ossification: Bone Formation
Bones form by replacing connective tissues in the fetus.
Some form within sheet-like layers of connective tissue (intramembranous bones), while others replace masses of cartilage (endochondral bones).
begins week 6 of development

17. Ossification

18. Intramembranous Bone development
The broad, flat bones of the skull form as intramembranous bones.
Osteoblasts deposit a bony matrix around themselves in all directions, forming spongy bone.
Once the deposited bony matrix completely surrounds the osteoblasts, they are then called osteocytes.

19. Intramembranous Ossification

20. Intramembranous Bone development
4. Cells of the membranous tissue that lie outside the developing bone give rise to the periosteum.
5. Osteoblasts on the inside of the periosteum form a layer of compact bone over the spongy bone.
6. The formation of bone is referred to as ossification.

21. Intramembranous Bone Development

22. Ossification: Bone Formation
Development of bone:
Video: Intramembranous vs Endochondral:
How to grow a bone:

23. Endochondral Bones 23

24. Endochondral bone development
Most of the bones of the skeleton fall into this category.
They first develop as hyaline cartilage models shaped like the future bones and are then replaced with bone.
Cartilage calcifies and is broken down in the diaphysis
Disintegrating cartilage is invaded by blood vessels and osteoblasts that first form spongy bone at the primary ossification center in the diaphysis.

26. Endochondral bones, cont.
4. Secondary ossification centers appear later in the epiphyses.
A band of hyaline cartilage, the epiphyseal plate, remains between the two ossification centers.
Layers of cartilage cells undergoing mitosis make up the epiphyseal plate. 26

27. Endochondral bones, cont.
7. Osteoclasts break down the calcified matrix and are replaced with bone-building osteoblasts that deposit bone in place of calcified cartilage.
8. A long bone continues to lengthen while the cartilaginous cells of the epiphyseal plate are active. Once the plate ossifies, the bone is done growing in length.
The medullary cavity forms in the diaphysis due to the activity of osteoclasts. 27

28. 2. ENDOCHONDRAL OSSIFICATION
*replacement of original hyaline cartilage models by bone
(continues until approx. age 25)
Continual mitosis of epiphyseal plate cartilage & replacement
by diaphysis bone = Elongation

30. Bone Elongation Animation
To show not listen to (good intro image)
X-Rays of Epiphysial plate:

31. Bone Elongation Not all bones lengthen
Takes place at the Epiphysial Plate
Made of cartilage –fills in with bone
Osteoclasts remove outer layer of calcified cartilage
Additional cartilage fills in
Older cartilage nearest diaphysis calcifies to create new bone
Epiphysial Plate becomes solid (calcified) Epiphysial Line by adulthood.
Plate = with cartialage
Line = NO cartilage, just bone

32. BONE GROWTH

34. Epiphyseal Plate

35. Epiphyseal Plate

36. Epiphyseal Line

37. Epiphyseal Plate or Line
Adult or Child?
Images are from
Answer
Epiphyseal Plate   or   Line
Adult   or   Child

38. Achondroplastic Dwarfism

39. Achondroplastic Dwarfism
Long bones stop growing in childhood
Short in stature but generally large head
Usually about 4 feet
Failure of chondrocytes of metaphysis to multiply and enlarge
Autosomal Dominant disorder

40. Osteitis Deformans (Paget disease)

41. Paget disease
Bone is excessively broken down (osteoclast activity) and reformed (osteoblast activity)
Resulting bone is structurally unstable and immature
Osteoclasts are 5x larger than normal (resorbing bone too fast), in response, normal size osteoblasts deposit new bone quickly, but its poorly formed

42. Bone Widening

43. Bone Widening Bone built up from outside: Osteoblasts
Bone broken down from inside: Osteoclasts
Megullary Cavity increases in size
Osteocytes secrete bone around a blood vessel
Claude

44. Bone Widening Animation

45. Bone Widening Animation

46. Rickets

47. Rickets Caused by Vitamin D deficiency in childhood
Vit D crucial for calcium and phosphorus absorption in digestive tract
Not enough minerals so bones are too flexible
During Industrial Revolution, a lot of children who worked in factories (little exposure to sunlight and malnourished)
Starting to increase again in urban US because spending so much time in doors and drinking soda instead of milk