Bones

Question 1

Bone development - types? definition?

Answer 1

Types:

• intramembranous ossification (in the membrane)
• endochondral ossification (in cartilage)

Question 2

What does ossification involve? Overview? lamellar bone types?

Answer 2

Ossification process:

• both cases replacement of CT with woven bone (osteoid) occurs
• woven bone (immature unmineralised bone) is remodelled to lamellar bone (mature) impregnated with Ca salts (Ca hydroxyapatite crystals)
• lamellar bone can either be compact, cortical, spongy or alveolar

Question 3

Intramembranous ossification - Areas? When? What occurs?

Answer 3

Areas:
- vault of skull, maxilla and mandible
When:
- 8th week of gestation
What occurs:
- mesenchymal cells differentiate into osteoblasts and lay down woven bone
- osteoid matrix becomes mineralised prod # of ossification centres
- osteoprogenitor cells at centre divide by mitosis and prod more osteoblasts
- ossification centres grow by addition of woven bone then becoming ossified (mineralised)
- some mesenchymal cells become bone marrow

Question 4

Endochondral ossification - Areas? What occurs?

Answer 4

Areas:
- majority of body bones (allow stresses to be sustained during growth)
What occurs:
- solid hyaline cartilage model of future bone created by chondrocytes
- interstitial growth creates elongated shape forming epiphyses, diaphysis and the perichondrium (still cartilage)
- shaft of the diaphysis, chondrocytes enlarge and begin to resorb cartilage leaving trabecular matrix
- trabecular matrix ossifies and the chondrocytes degenerate leaving space
- BVs and mesenchymal cells invade diaphysis spaces
- perichondrium becomes periosteum
- osteoblasts in periosteum create bone on surface of diaphysis
- mesenchymal cells form osteoblasts and bone marrow cells
- osteoblast begin to create woven bone on trabeculae
- primary centres formed but cartilage epiphyses with bony centre in middle of diaphysis
- between epiphyses and diaphysis lies epiphyseal growth plate
- epiphyseal side more cart is laid
- diaphyseal side chondrocytes replaced by osteoblasts (bone form)
- allowing continual lengthening of diaphysis
- centre of epiphysis, a 2nd centre of ossification forms and epiphyseal ossification begins
- thin layer of cartilage at joint surface
- woven -> impreg -> Ca hydroxyapatite -> lamellar
- on maturity, epiphyseal plates fuses (growth ceases)

Question 5

Epiphyseal plate - histo definition?

Answer 5

Histo definition:

- zones between epiphysis and diaphysis

Question 6

Epiphyseal growth plate - zones?

Answer 6

Zones:

• reserve cartilage (chondrocytes)
• proliferation (mitosis, columns)
• maturation (no division, cells increase)
• hypertrophy (chondrocytes lage and vacuoled, matrix calcifies)
• degeneration (chondrocytes dege, osteogenic invade lacunae)
• osteogenic (osteogenic cells become osteoblasts and converge on trabecular remnants of cart matrix, blasts make bone)

Question 7

Bone dynamics - definition? characteristics? factors?

Answer 7

Definition:
- living tissue which responds to demands of environment
Characteristics:
- continual remodelling
Factors:
- stress, trauma and load bearing
- health, nutrition and hormones

Question 8

Bone remodelling cycle - process? what occurs in bone?

Answer 8

Resting phase
Activation:
- osteoclasts remodelling resorbs bone (10-20 days)
Reversal:
- osteoclast apoptosis
Formation:
- bone form (3-6 months)
What occurs in bone:
- tunnel bored through compact bone by osteoclasts
- bone deposit begins on wall (remodelling unit)
- advancing cutting cone (active osteoclasts) followed by capillary loops and dividing cells (osteoclasts form the new Haversian system
- closing cone (osteoblasts) lay new bone (lamellae to create rings of bone around central canal)

Question 9

Alveolar bone remodelling - Factors?

Answer 9

Factors: application of Pa
- compression (resorption)
- tension (deposition)
Normally depends on functional stum from the stresses of mastication to preserve structure

Question 10

Bone turnover - cortical role? trabecular role? alveolar bone reduction?

Answer 10

Cortical role:
- denser and more calcified than trabecular providing strength on outer surfaces
Trabecular role:
- mostly in epiphyses (and shaft), vertebrae and femoral neck
- higher turnover rate (prone bone loss)
- areas prone to fracture with old age
Alveolar bone resorbed when mastication stresses reduced

Question 11

Repair following a fracture - Process?

Answer 11

• Formation of a clot
• Replaced by provisional callus
• Callus strengthened by Ca salts
• Osteogenic cells in endosteum and periosteum lay down woven bone (bony callus)
• Bony union, woven bone becomes lamellar bone

Question 12

Relationship between bone and diet?

Answer 12

Relationship:

• lack Ca (osteoporosis)
• lack vit D (osteomalacia, rickets, disturb ability to calcify bone, weak bone)
• lack vit C (scurvy affects growth plates collagen and proteoglycan prod)
• lack vit A (interfere ability to erode bone, no turnover balance)