Bones and Calcium

Question 1

What is the principle reservoir for calcium and potassium?

Answer 1

Bone.

Question 2

What is osteoporosis?

Answer 2

The breaking of bones due to calcium deficiency.

Question 3

What is osteopenia?

Answer 3

Weakening of bones (not as bad as osteroporosis)

Question 4

What is osteopetrosis?

Answer 4

The hardening of bones, causing them to become inflexible and brittle.

Question 5

Why is the regulation of calcium important?

Answer 5

1. Bone structure
2. Excitability of cells
3. Intracellular signalling

Question 6

Where are the blood’s three sources of calcium/phosphate?

Answer 6

Bone, kidney, and heart.

Question 7

What two hormones are most important in calcium regulation?

Answer 7

Vitamin D3 and PTH

Question 8

What are the two cells in bone?

Answer 8

Osteoblasts and osteoclasts

Question 9

What effect does D3/PTH have on bone?

Answer 9

Increases breakdown of matrix for bone resportion.

Question 10

How are osteoclasts activated?

Answer 10

Secretion of RANK from osteoblasts after activation by PTH/D3 activates osteoclast production.

Question 11

What is the net effect of PTH?

Answer 11

Bone: increase calcium/phosphate resorption into blood
Kidney: increase calcium absorption but increase phosphate excretion

Stimulates vitamin D processing in kidney

Question 12

Why is phosphate excreted via PTH?

Answer 12

Calcium and phosphate form a precipitate.

Question 13

How is vitamin D metabolized?

Answer 13

1. Vitamin D3 converted to 25-OH-D3 in liver (by 25-hydroxenase)
2. Forms either 1,25-OH-D3 or 24,25-OH-D3

Question 14

When is 1,25-OH-D3 (CALCITRIOL) formed?

Answer 14

Low calcium, PTH

Question 15

When is 24, 25-OH-D3 (SECALCIFEROL) formed?

Answer 15

High calcitriol, high calcium.

Question 16

What is the net effect of D3?

Answer 16

1. Kidney: increased calcium and phospate reabsorption
2. Promotes bone resorption
3. Promotes uptake of phosphate and calcium from gut.

Question 17

What are calcium levels sense by?

Answer 17

Calcium receptors in the parathyroid.

Question 18

What is hypocalcemia?

Answer 18

Low levels calcium.

Question 19

What are short term resolutions to hypocalcemia?

Answer 19

Calcium or D3 metabolites.

Question 20

What is the acute effect of hypocalemia?

Answer 20

1. Hyperexcitability of cells, causing Trousseau’s sign. May lead to seizures and spasms if unresolved.

Question 21

What are long term dangers of hypocalemia?

Answer 21

Secondary hyperparathyroidism; increased PTH levels causing bone resorption and osteoporosis.

Question 22

What is typically the cause of secondary hyperparathyroidism?

Answer 22

Hypoparathyroidism, Vitamin D deficiency

Question 23

What is hypercalcemia?

Answer 23

High levels of calcium

Question 24

What are acute effects of hypercalcemia?

Answer 24

Loss of cellular excitability.

Question 25

What is the typical cause of hypercalcemia (long term)?

Answer 25

Primary hyperparathyroidism; overactivity via tumor.

Question 26

How is primary hyperparathyroidism treated?

Answer 26

Resection of the parathyroid and subsequent treatment via therapeutics: calcimimetics and bone protectants.

Question 27

What gender is osteoporosis most common in? Why?

Answer 27

Post-menopausal women due to lack of estrogen (which builds up bones)

Question 28

How is osteoporosis treated in post-menopausal females?

Answer 28

Hormone replacement, estrogen mimetics

Question 29

What are common causes of osteoporosis?

Answer 29

Glucocorticoid administration, hyperparathyroidism.

Question 30

What are bisphosphonates?

Answer 30

Inhibit osteoclasts by binding to bone matrix (contain phosphates, can bind to calcium) to kill osteoclasts and inhibit glucocorticoids.