bone physiology

Question 1

process of bone formation

Answer 1

ossification

Question 2

name the production of bone

Answer 2

osteogenesis

Question 3

ossification

Answer 3

6 weeks after fertilisation

Question 4

name the two developments of bone

Answer 4

Intramembranous ossification

Endochondral ossification

Question 5

Intramembranous ossification

Answer 5

conversion of mesenchyme directly into bone
only in flat bones
only in utero

Question 6

general process of intramembranouse ossification

Answer 6

1. Mesenchyme differentiates into osteoblasts
2. Osteoblasts group into clusters and form ossification centres
3. Osteoblasts begin secreting osteoid until they are surrounded
4. Binding of calcium hydroxyapatite hardens extracellular matrix
5. Extracellular matrix surrounds blood vessels and forms spongy bone
6. Mesenchymal cells on surface of bone differentiate to form periosteum
7. Osteoblasts inside periosteum secrete osteoid forming compact bone

Question 7

endrochondral ossification

Answer 7

conversion of all cartilage into bone
all other bones apart from flat bones
more common type of bone formation

Question 8

generalised process of endrochondral ossification

Answer 8

1. Mesenchyme differentiates into chondroblasts
2. Chondroblasts secrete extracellular matrix to form cartilage model for bone
3. Chondrocytes proliferate and alter extracellular matrix enabling mineralization
4. Mineralization prevents nutrients reaching chondrocytes causing apoptosis
5. Apoptosis allows blood vessels to invade bringing osteoblasts and osteoclasts
6. Osteoblasts trigger transformation of perichondrium to periosteum
7. Osteoclasts breakdown extracellular matrix to form medullary cavity
8. Osteoblasts form a periosteal collar of compact bone around the diaphysis
9. Chondrocytes continue to proliferate at epiphyses increasing bone length

Question 9

types bone growth

Answer 9

appositional growth

Interstitial growth

Question 10

Appositional growth

Answer 10

growth resulting in an increase in thickness or diameter

occurs throughout lifetime

Question 11

Interstitial growth

Answer 11

growth resulting in an increase in length.
occurs at epiphysis plate at epiphyseal side
cartilage is replaced by bone

Question 12

epiphyseal plate

Answer 12

a plate of hyaline cartilage only in children
site of all interstitial growth
in adults it is fully ossified and is called a line
done by age 25

Question 13

damage to epiphyseal

Answer 13

stunted growth

Question 14

zones of cartilage in epiphyseal plate

Answer 14

Zone of calcified cartilage: Only a few cells thick. Mostly
dead chondrocytes surrounded by calcified extracellular
matrix. Osteoclasts dissolve calcified cartilage. Osteoblasts
secrete extracellular matrix, replacing calcified cartilage via
endochondral ossification. (middle of bone)

Zone of hypertrophic cartilage: Large, maturing
chondrocytes arranged in columns

Zone of proliferating cartilage: Slightly larger chondrocytes,
stacked like coins. Divide and secrete extracellular matrix.

Zone of resting cartilage: Small, scattered chondrocytes.
Anchors epiphyseal plate to epiphysis of bone. No growth. (end of bone)

Question 15

bone remodelling types

Answer 15

the continuous replacement of bone tissue
bone resorption
bone deposition

Question 16

bone resorption

Answer 16

removal of minerals and collagen fibres from bone extracellular matrix through osteoclasts

Question 17

bone deposition

Answer 17

the addition of minerals and collagen fibres through osteoblasts

Question 18

factors affecting bone remodelling and growth

Answer 18

minerals
vitamin
hormones
mechanical stress

Question 19

minerals

Answer 19

calcium, phosphorus

minerals for extracellular matrix

Question 20

vitamens

Answer 20

• Vitamin A –inhibits load-induced osteoblast activity
• Vitamin C –essential in the production of collagen
• Vitamin D –essential for absorption of calcium

Question 21

Hormones

Answer 21

• Growth hormone –stimulates bone growth and remodelling
• Thyroid hormones –influence chondrocytes, osteoblasts, osteoclasts
• Sex hormones –growth, bone density, closure of epiphyseal plate
• Parathyroid and calcitonin –regulate blood calcium

Question 22

mechanical stress

Answer 22

• Bone will adapt to the loads under which it is placed (Wolff’s Law)
• Increased load = increased bone remodelling
• Trabeculae undergoes adaption to resist stress
• Mechanical stress sensed by osteocytes

Question 23

wolfs law

Answer 23

load increases - bone increases density to withstand load

Question 24

fracture

Answer 24

any brake in a bone

Question 25

fracture types

Answer 25

open fracture
closed (simple) fracture
comminuted fracture
green stick fracture - only in children 
impacted fracture
epiphyseal plate fracture

Question 26

steps of fracture repair

Answer 26

REACTIVE
REPARATIVE
REMODELLING

Question 27

Reactive phase:

Answer 27

Broken blood vessels at fracture site. Fracture haematoma forms
6-8 hrs after injury. Bone cells in area die triggering swelling and inflammation.
Phagocytes and osteoclasts remove dead and damaged tissue.

Question 28

Reparative phase:

Answer 28

Blood vessels grow into haematoma. Fibroblasts and
chondroblasts invade fracture site producing collagen fibres and fibrocartilage.
Fibrocartilage callus bridges broken ends of bones. Osteoblasts begin to produce
trabeculae. Fibrocartilage is converted to spongy bone forming bony callus.

Question 29

Remodelling phase: Compact bone replaces spongy bone around periphery of
fracture. Osteoclasts and osteoblasts undertake bone remodelling and bone
returns to original shape.