physiology of bone formation and repair

Question 1

What do too much bone resorption and too much bone formation result in

Answer 1

osteoporosis and osteopetrosis respectively

Question 2

What are the 2 main types of bone

Answer 2

long bone and flat bone

Question 3

how are bones further classified

Answer 3

macroscopic

• cortical bone (thick hard bone on the outside)
• cancellous (spongy, inside), has spicules and trabeculae

microscopic

• lamellar (osteons)
• woven (immature and disorganised)

Question 4

What composes the bone

Answer 4

living cells and acellular matrix
3 types of cells
-osteoclasts (destructive part of bone, catabolic)
-osteocytes (maintenance of bone)
-osteoblasts (regulate bone growth)

Question 5

How do osteocytes develop

Answer 5

Osteocytes arise from osteoblasts

Question 6

describe osteoclasts

Answer 6

they can proliferate,
phagocytose bone matrix and crystals
secrete acids and proteolytic enzymes

Question 7

What are the properties of the extracellular matrix in bone

Answer 7

70% minerals,
plus abundant proteins and sparse cells
high compressive strength and tensile strength

Question 8

Where are glycosaminoglycans

Answer 8

primarily a sugar molecule which is found in bone and cartilage,

highly negative repels each other, attracts water and resists compression.

Question 9

Where are growth factors found in the bone

Answer 9

They are suspended in the matrix, they are revealed by osteoclast action, which leads to proliferation and mineralisation.

bone remodelling= activation-resorption-formation sequence.

Question 10

briefly outline the process of bone remodelling

Answer 10

osteoclasts resorb bone,

osteoblasts deposit bone and lays done bone (in different directions) and then

Question 11

What are the 2 factors that determine remodelling

Answer 11

recurrent mechanical stress
calcium homeostasis (plasma calcium is essential in maintaining the structural integrity of the skeleton)

Question 12

How does mechanical stress strengthen bone

Answer 12

Inhibits bone resorption, promotes deposition

without weight-bearing, bone rapidly weakens.

Question 13

What type of drugs are used for osteoporosis, give an example and how they work

Answer 13

e.g. bisphosphonates, alendronate inhibits osteoclast-mediated bone resorption

Question 14

What are 2 meds apart from alendronate that is used for osteoporosis?

Answer 14

teriparatide encourages osteoblast formation of bone

denosumab, prevent osteoclast maturation.

Question 15

describe the molecular mechanism of osteopetrosis

Answer 15

osteoblasts cannot remodel bone,

defective vacuolar proton pump or defective chloride channel.

Question 16

What does osteopetrosis result in

Answer 16

Excess bone growth, at the foramina, may press on nerves

brittle (dense) bones
blindness
deafness
severe anaemia.

Question 17

What hormones are involved in calcium regulation

Answer 17

PTH - parathyroid hormone, increases plasma calcium

Vit D- increases plasma calcium

calcitonin, made by thyroid c cells,
tones down blood calcium

Question 18

What are some of the functions of vitamin D

Answer 18

increases intestinal calcium absorption
stimulates kidneys to reabsorb calcium
stimulates osteoclasts indirectly (via osteoblasts)
vit D facilitates bone remodelling.

Question 19

What are some causes of low plasma calcium

Answer 19

loss

• pregnancy
• lactation
• kidney dysfunction

low intake

• insufficient ingestion of calcium
• rickets

parathyroid dysfunction

Question 20

What does chronic hypocalcaemia result in

Answer 20

Skeletal deformities
an increased tendency toward bone fractures
impaired growth
short stature
dental deformities.