Topic 9: Skeletal System - Bone Growth (postnatal)

Question 1

What is bone growth in length?

Answer 1

• endochondral growth at epiphyseal plates

Question 2

How does bone grow in length? (2)

Answer 2

• cartilage grows and matrix near diaphysis becomes bone
• growth in length stops when epiphyseal plate ossifies into epiphyseal line (closure)

Question 3

What is bone growth in diameter called?

Answer 3

• appositional growth
  aka bone remodelling

Question 4

How does bone grow in diameter? (2)

Answer 4

• osteoblasts beneath periosteum secrete bone matrix (external bone surface)
• osteoclasts resorb bone on the endosteal surface
• then size of cavity keeps place with growing bone
  think outside is growing and inside is taking it away??

Question 5

What are 3 factors affecting bone growth/remodelling?

Answer 5

• mechanical stress
• Nutrition
• Hormones

Question 6

How does mechanical stress affect bone growth? Use execise, injury, and weights/electric currents as an example

Answer 6

• due to muscle action
  1. Moderate exercise increases osteblast activity in areas of stress (more building than breakdown)
  2. Injury that restricts movement decreases osteoblast activity and no change in osteoclast activity decreases bone mass
  3. Weights or electric currents may speed healing by increasing osteoblast activity

Question 7

Which vitamins and minerals are needed for nutrition of bones? (4)

Answer 7

Ca2+ and PO4-
Vitamin C and D

Question 8

Why do we need Ca2+ and PO4-?

Answer 8

required for bone matrix production

Question 9

Why do we need vitamin C?

Answer 9

• for collagen production

Question 10

Why do we need vitamin D? (2)

Answer 10

• increase absorption of calcium from intestine
• lacking vit D causes rickets (soft bones)

Question 11

Which hormones are needed for bone growth/remodelling? (5)

Answer 11

• GH
• thyroid
• E and Testosterone
• Calcitonin
• PTH

Question 12

Why do we need GH and Thyroid hormone?

Answer 12

stimulate bone growth

Question 13

Why do we need estrogen and testosterone for bones? (2)

Answer 13

• increases ostebclast activity
• Estrogen (both sexes) helps ossification of epiphyseal plate (to line)

Question 14

What is the function of calcitionin? (2)

Answer 14

• inhibits osteoclast activity
• increases calcium movement from blood to bone to promote bone growth

Question 15

What is the function of PTH?

Answer 15

• Increases osteoclast activity and decreases osteoblast activity to increase blood calcium

Question 16

What is osteoporosis?

Answer 16

• decrease in bone mass

Question 17

What are the risk factors to osteoporosis (7)

Answer 17

• increasing age (decrease in sex hormones)
• post menopause (decrease E)
• inadequate diet (decreased vit D, Ca2+)
• illness, excess PTH
• too little/excessive exercise (stress - cortisol)
• Drugs like cortisone and alcohol (decreases osteoblast activity)
• smoking (decreases E)

Question 18

What is the process for bone repair? (3)

Answer 18

1) begins with formation of a blood clot
2) replaced by a callus
3) callus ossifies - both intramembranous and endochondral

Question 19

What is a callus made of?

Answer 19

• fibrous network and fibrocartilage isletsq

Question 20

How long does bone repair take? (2)

Answer 20

4-6 weeks (depends on age and diet)
- cast required since movement can refracture new matrix