Pathophysiology of Bone Disorders and Osteoporosis

Question 1

what happens to bones as we age?

Answer 1

they become thinner and weaker

Question 2

what is Wolff’s law?

Answer 2

Every change in function of bone is followed by certain definite changes in its internal architecture and its external conformation.

Question 3

how does the parathyroid hormone regulate calcium?

Answer 3

it increases calcium levels by:

1. Stimulating osteoclasts to degrade bone and release Ca2+ into blood
2. Increasing intestinal absorption of calcium
3. Decreases calcium excretion at kidneys

Question 4

what is secreted from the thyroid gland to reduce calcium ion levels and how does it do this?

Answer 4

Calcitonin is secreted and it reduces calcium ion levels by:

1. inhibiting osteoclast activity
2. increasing calcium excretion at kidneys

Question 5

what effect does a rise in blood calcium have on the thyroid gland to then reduce calcium levels?

Answer 5

It triggers the thyroid to release calcitonin which then stimulates Ca2+ salt deposit in bone

Question 6

what is the most common cause of Rickets/Osteomalacia?

Answer 6

severe, prolonged vitamin D deficiency

Question 7

what is the pathogenesis of rickets?

Answer 7

1. normal bone is formed

2. the body can not fully mineralize the newly formed osteoid tissue, resulting in decreased bone strength

Question 8

how is rickets treated?

Answer 8

with high-doses of vitamin D

Question 9

what are the main areas affected by Paget’s disease?

Answer 9

skull, spine, pelvis, femur, and tibia

Question 10

what is the pathogenesis of Paget’s disease?

Answer 10

• An accelerated bone formation does not allow for proper layering of collagen leading to disorganized or woven collagen.
• this causes reduced mineralization causing spotty weakening of bone

Question 11

how is Paget’s disease treated?

Answer 11

• Bisphosphonates as they work directly on osteoclasts to slow down bone turnover, allowing more time for proper bone formation
• Subcutaneous or intramuscular calcitonin can be used if bisphosphonates therapy is contraindicated.

Question 12

which two hormones help maintain bone mass to prevent osteoporosis?

Answer 12

Estrogens and androgens

Question 13

what is postmenopausal osteoporosis (type I)?

Answer 13

When oestrogen deficiency causes:
• increased proliferation and activation of osteoclasts
• prolongs survival of osteoclasts
Therefore more bone breakdown

Question 14

what is senile osteoporosis (type II)?

Answer 14

Bone loss due to:
• increased bone turnover
• Malabsorption
• Mineral and vitamin deficiency

Question 15

what is used to diagnose osteoporosis?

Answer 15

Bone mineral density (BMD)

Question 16

where are Bone mineral density (BMD) measurements usually taken?

Answer 16

at lumbar spine and hip

Question 17

what does a T score between -1 and -2.5 indicate?

Answer 17

osteopenia

Question 18

what does a T score equal to or less than -2.5 indicate?

Answer 18

osteoporosis

Question 19

what does a T score less than -2.5 with a fracture indicate?

Answer 19

established osteoporosis

Question 20

what is the active form of vitamin D?

Answer 20

1,25-(OH)2-D = calcitriol

Question 21

where is RANKL released from and what does it do?

Answer 21

• secreted by osteoblasts and bone marrow stromal cells

- mediates osteoclast differentiation, activation, and survival and primary mediator of bone resorption.

Question 22

what does Osteoprotegerin (OPG) do?

Answer 22

provides alternative binding site for RANKL acting as decoy receptor, so it cannot activate osteoclast cellular signalling preventing bone resorption/breakdown