Bone Mineral Homeostasis

Question 1

What are osteoblast, osteoclasts, and osteocytes responsible for?

Answer 1

Osetoblast: bone building
Osteoclast: breakdown of bone
Osteocytes: storage of Ca++ and bone repair

Question 2

How can glucocorticoid-induced osteoporosis occurs?

Answer 2

Inhibit osetoblast activity
Stimulate osteoclast proliferation
Decrease intestinal absorption of Ca
Increase Ca excretion by the kidneys

Question 3

When is the highest rate of bone loss related to glucocorticoid-induced osteoporosis?

Answer 3

Early in therapy

Question 4

How can glucocorticoid-induced osteoporosis be prevented?

Answer 4

Ca++/vit D, biphosphonates, lifestyle modifications (ex-weight lifting)

Question 5

In addition to bone formation what else is Ca important for?

Answer 5

NT release, muscle contraction, and blood coagulation

Question 6

Changes in ______ levels affect plasma Ca++ levels.

Answer 6

phosphate

Question 7

What three things mediate calcium/phosphate homeostasis?

Answer 7

PTH
Vit D
Calcitionin

Question 8

How does endogenous PTH affect bone and Ca++?

Answer 8

Modulates bone resorption and stimulates tubular resorption of Ca

Question 9

How do high and low plasma Ca++ concentrations affect PTH levels?

Answer 9

High Ca++ suppresses PTH secretion

Low Ca++ stimulates PTH secretion

Question 10

Cholecalciferol and Ergocalciferol are both _____ __ administered through dietary sources/supplements/absorbed from skin

Answer 10

Vit D
Cholecalciferol (vit D3) sun and animal sources
Ergocalciferol (vit D2) plants sources

Question 11

How are Cholecalciferol (vit D3) and Ergocalciferol (vit D2) converted to their active form, calcitrol?

Answer 11

Converted in the liver to 25-hydroxylase which is then converted to 1, 25 hydroxylase vit D which is the active form of vit D

Question 12

What is the role of vit D once it is activated?

Answer 12

Increase absorption of dietary Ca++

Question 13

What is produced by the thyroid gland in response to hyperglycemia?

Answer 13

Calcitonin (opposes PTH)

Question 14

How does Calcitonin work?

Answer 14

Released in response to hypercalcemia
Binds to receptors of osteoclasts and inhibits its activity
= Dec bone resorption, dec plasma Ca++ levels

Question 15

How does CKD affect bone mineral homeostasis?

Answer 15

Secondary hyperparythyroidism

Question 16

What is hyperparathyroidism in CKD a result of?

Answer 16

Hypocalcemia (inc. PTH)
Hyperphosphatemia (kidneys unable to excrete phosphate to normal extent)
Dec. production of calcitrol (active form of vit D)
=enhanced bone resorption

Question 17

As blood Ca++ rises what happens to phosphate levels?

Answer 17

They begin to fall

Question 18

Treatment of CKD related hyperparathyroidism include drugs that:

Answer 18

1. Lower plasma phosphate levels (oral phosphate binders)

2. Decrease PTH synthesis and secretion (vit D, vit D analogues, calcimimetics)