Microscopic Structure of Bone

STRUCTUREA. 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)

STRUCTUREA. COMPACT BONE – strong, weight-bearing, stress-resisting bone with few spaces

1. OSTEON “HAVERSIAN SYSTEM”– repeating unit, run length of shaft

STRUCTUREA. 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

STRUCTURECOMPACT BONE – strong, weight-bearing, stress-resisting bone with few spaces

3. LAMELLAE – rings of hard calcified matrix surrounding haversion canals

STRUCTURECOMPACT 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

STRUCTUREA. COMPACT BONE – strong, weight-bearing, stress-resisting bone with few spaces

5. LACUNAE – small openings containing osteocytes -between lamellae

STRUCTUREA. 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

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)

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

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

STRUCTURE

STRUCTURE

STRUCTUREA. COMPACT BONE

1. OSTEON “HAVERSION SYSTEM”2. HAVERSION (CENTRAL) CANALS3. LAMELLAE4. PERFORATING (VOLKMANN’S) CANALS5. LACUNAE6. CANILICULI

A.

B.

C.

D.

B.

E.

D.

F.

F.

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

Ossification

Intramembranous Bone development

1. The broad, flat bones of the skull form as intramembranous bones.

2. Osteoblasts deposit a bony matrix around themselves in all directions, forming spongy bone.

3. Once the deposited bony matrix completely surrounds the osteoblasts, they are then called osteocytes.

Intramembranous Ossification

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.

Intramembranous Bone Development

Ossification: Bone Formation

Development of bone:https://www.youtube.com/watch?v=xXgZap0AvL0

Video: Intramembranous vs Endochondral:http://www.youtube.com/watch?v=p-3PuLXp9Wg

How to grow a bone:https://www.youtube.com/watch?v=xXgZap0AvL0

Endochondral Bones

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Endochondral bone development1. Most of the bones of the skeleton fall into this category.2. They first develop as hyaline cartilage models shaped like the future bones and are then replaced with bone. 3. Cartilage is broken down in the diaphysis and progressively replaced with bone while the periosteum develops on the outside.4. Disintegrating cartilage is invaded by blood vessels and osteoblasts that first form spongy bone at the primary ossification center in the diaphysis.

Endochondral bones, cont.5.Osteoblasts from the

periosteum lay down compact bone around the primary ossification center.

6.Secondary ossification centers appear later in the epiphyses.

7.A band of hyaline cartilage, the epiphyseal plate, remains between the two ossification centers.

8.Layers of cartilage cells undergoing mitosis make up the epiphyseal plate. 26

Endochondral bones, cont.

9.Osteoclasts break down the calcified matrix and are replaced with bone-building osteoblasts that deposit bone in place of calcified cartilage.

10.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.

11.The medullary cavity forms in the diaphysis due to the activity of osteoclasts.

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9. Continual mitosis of epiphyseal plate cartilage & replacement by diaphysis bone = Elongation

B. ENDOCHONDRAL OSSIFICATION (vast majority of bones; pp. 140-41)*replacement of original hyaline cartilage models by bone (continues until approx. age 25)

Bone Elongation Animation

• To show not listen to (good intro image) • http://highered.mcgraw-hill.com/sites/0072

495855/student_view0/chapter6/animation__osteoporosis.html

• X-Rays of Epiphysial plate:• http://www.youtube.com/watch?v=Plvd7esl

g-Q

Bone Elongation1. Not all bones lengthen

2. Takes place at the Epiphysial Plate – Made of cartilage –fills in with bone

3. Osteoclasts remove outer layer of calcified cartilage

4. Additional cartilage fills in

5. Older cartilage nearest diaphysis calcifies to create new bone

6. Epiphysial Plate becomes solid (calcified) Epiphysial Line by adulthood.

– Plate = with cartialage– Line = NO cartilage, just bone

BONE GROWTH

Epiphyseal Plate

Epiphyseal Plate

Epiphyseal Line

Adult or Child?

Images are from http://www.dartmouth.edu/~anatomy/knee/radiographs/radio3.html

Answer

Epiphyseal Plate   or   Line Epiphyseal Plate   or   Line

Adult   or   Child Adult   or   Child

Bone Elongation Animation

• To show not listen to (good intro image) • http://highered.mcgraw-hill.com/sites/0072

495855/student_view0/chapter6/animation__osteoporosis.html

• X-Rays of Epiphysial plate:• http://www.youtube.com/watch?v=Plvd7esl

g-Q

Bone Widening Animation

• http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter6/animation__bone_growth_in_width.html

Bone Widening 1. Bone built up from outside: Osteoblasts

2. Bone broken down from inside: Osteoclasts– Megullary Cavity increases in size

3. Osteocytes secrete bone around a blood vessel

Claude

Bone Widening Animation

• http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter6/animation__bone_growth_in_width.html

• Epiphyseal fracture-BONE GROWTH

BONE FRACTURE REPAIR

• Epiphyseal fracture-

Type II fracture of the distal phalanx of the first toe

BONE GROWTH

Growing Pains15 % of children experience, occasional nighttime leg pain

Described as an ache or throb in the legs

Often strike late afternoon, early evening or awaken a child at night

There is no evidence that growth is painful, but…

Probably Cause:overuse during the day

Achondroplastic Dwarfism

Achondroplastic Dwarfism

• Long bones stop growing in childhood• Failure of chondrocytes of metaphysis to

multiple and enlarge• Autosomal Dominant disorder