1.2 Bone Growth and Repair

Question 1

Two patterns of bone formation

Answer 1

1) intramembranous ossification

2) endochondral ossification

Question 2

4 steps of intramembranous ossification

Answer 2

1) development of the ossification center
- –specific chemical messages cause mesenchyme to cluster and differentiate to osteoprogenitor cells then osteoblasts; osteoblasts secrete the organic extracellular matrix of bone

2) calcification
- – secretion stops and the cells (now osteocytes) extend towards canaliculi; in a few days, calcium and other mineral salts are deposited and extracellular matrix hardnes

3) formation of trabeculae
- – extacellular matrix forms and develops into trabeculae, where blood vessels associated with it then differentiates into red bone marrow

4) development of the periosteum
- –mesenchyme condenses at the periphery of the bone and develops into the periosteum

Question 3

endochondral ossification

Answer 3

replacement of cartilage by bone

most bones are formed this way

Question 4

chondroblasts

Answer 4

secrete cartilage extraceullar matrix, producing a cartilage model made of hyaline cartilage

note: the perichondrium is the covering around the cartilage model

Question 5

steps of endochondral ossification

Answer 5

1) development of the cartilage model
- –special chemical signals causes mesenchyme to cluster and form chondroblasts

2) growth of the cartilage model
- –this model grows in length by continual cell division of chondrocytes, and with further secretion of ECM

3) Development of primary ossification center
4) development of medullary (marrow) cavity
5) development of the secondary ossification centers
6) formation of articular cartilage and the epiphyseal (growth) plate

Question 6

interstitial (endogenous) growth

Answer 6

type of cartilaginous growth

Question 7

appositional (exogenous) growth

Answer 7

growth of cartilage in thickness due to deposition of ECM on the cartilage surface of the model by new chondroblasts

Question 8

growth in length of boen involves 2 major events

Answer 8

1) interstitial growth of cartilage on the epiphyseal side of the epiphyseal plate
2) replacement of cartilage on the diaphysial side of the epiphyseal plate with bone by endochonral ossification

Question 9

four zones of epiphyseal plate

Answer 9

zone resting cartilage

zone of proliferating cartilage

zone of hypertrophic cartilage

zone of calcified cartilage

Question 10

bone remodeling

Answer 10

ongoing replacement of old into new bone tissue

Question 11

bone resorption

Answer 11

removal of minerals and collagen fibers from bones by osteoclasts

Question 12

boen deposition

Answer 12

the addition of minerals and collagen fibers to bone by osteoblasts

Question 13

factors affect bone growth and remodeling

Answer 13

minerals, vitamins, and hormones

Calcium, phosphorus, magnesium, vitamin A, D, K and B12, and insulin-like growth factors (IGFs)

Question 14

Stress fracture

Answer 14

microscopic fissures in bone that forms w/o evidence of injury to other tissues

Question 15

repair phases of bone fracture

Answer 15

1. Reactive phace:
2. Reparative phase: fibrocartilaginous callus formation
3. Reparative phase: Bony calus formation
4. Bone remodeling phase

Question 16

Reactive phace:

Answer 16

early inflammatory phase where blood forms around site (called a fracture hematoma); phagocytes and osteoclasts remove and damaged the dead tissue

Question 17

Reparative phase: fibrocartilaginous callus formation

Answer 17

cells from periosteum develop into chondroblasts and produce fibrocartilage in this region

Question 18

Reparative phase: Bony calus formation

Answer 18

near the healthy bone tissue, osteoprogenitor ells become osteoblasts and produce spongy bone trabeculae (join the living and dead portions of the orig bone fragments)

Question 19

Bone remodeling phase

Answer 19

final phase; dead portions of orig fragment get slowly absorbed by osteoclasts.

compact bone replace spongy around the structure

Question 20

4 types of fracture

Answer 20

1. Open (compound): bone protrude through skin
2. Comminuted: into many pieces
3. Greenstick: broken on one side but the other bends
4. Impacted: forcefully driven into the interior of another

Question 21

parathyroid hormone

Answer 21

increases blood Ca2+ level

Question 22

calcitrol

Answer 22

hormone that promotes absorption of Ca2+ from food in the GI tract into the blood

Question 23

calcitonin

Answer 23

hormone that decreases blood Ca2+ level; inhibits the activityof osteoclasts and increases Ca2+ deposition