Ganong 24th ed - Chapter 21 - Calcium and Phosphate Endocrinology (1)

Question 1

Name two principle functions of PTH. Also, name some other function of PTH.

Answer 1

PTH mobilizes calcium from bones (it increases plasma Ca2+) and causes increased urinary excretion of phosphate (it decreases plasma phosphate).
PTH also increases renal reabsorption of calcium, and stimulates production of 1,25-dihydroxycholecalciferol, and this increases Ca2+ absorption from the intestine.

Question 2

Name two principle functions of PTH

Answer 2

PTH mobilizes calcium from bones (it increases plasma Ca2+) and causes increased urinary excretion of phosphate (it decreases plasma phosphate)

Question 3

What is another name for 1,25-dihydroxycholecalciferol?

Answer 3

Calcitriol

Question 4

What is the most predominant function of 1,25-dihydroxycholecalciferol? What else does it do?

Answer 4

1,25-dihydroxycholecalciferol mostly increases intestinal absorption of calcium, but it also increases renal absorption of calcium.

Question 5

Where is 1,25-dihydroxycholecalciferol produced? From which precursor molecule?

Answer 5

1,25-dihydroxycholecalciferol is produced in the kidneys, in the proximal tubule cells, from the precursor molecule calcidiol, which comes from the liver.

Question 6

What is the normal plasma level of 1,25-dihydroxycholecalciferol (calcitriol)?

Answer 6

0.03 ng/mL

Question 7

What does a change in plasma phosphate levels do to the production of 1,25-dihydroxycholecalciferol?

Answer 7

Production of 1,25-dihydroxycholecalciferol is stimulated by low plasma phosphate levels, and inhibited by high plasma phosphate levels.

Question 8

What does a change in plasma calcium levels to do the production of 1,25-dihydroxycholecalciferol?

Answer 8

Production of 1,25-dihydroxycholecalciferol is stimulated by low plasma calcium levels, and inhibted by high plasma calcium levels.

Question 9

How does calcium exist in plasma?

Answer 9

About half is ionized and diffusible, and about half is protein-bound. Also, about 6% is complexed to bicarbonate, citrate, etc.

Question 10

Why does hyperventilation produce tetany?

Answer 10

Because it increases plasma pH, which makes plasma proteins more ionized, which means that plasma proteins are more available to bind calcium –> hypocalcaemic tetany (neuromuscular hyperexcitability).

Question 11

What is calbindin?

Answer 11

This is an intracellular calcium-binding protein that is found in the epithelial cells of the intestinal brush-border, where calcium absorption occurs.

Question 12

What proportion of the body’s calcium is in the bones?

Answer 12

90% (in the form of hydroxyapatite, which is calcium phosphate salts)

Question 13

What proportion of the body’s phosphorus is in the bones?

Answer 13

90% (in the form of hydroxyapatite, which is calcium phosphate salts)

Question 14

What type of vitamin D is produced in the skin in response to sunlight?

Answer 14

Vitamin D3 (also called cholecalciferol)

Question 15

What happens to cholecalciferol after it is formed in the skin?

Answer 15

It is converted to 25-hydroxycholecalciferol in the liver.

Question 16

Where is 1,25-dihydroxycholecalciferol produced? From which precursor molecule?

Answer 16

1,25-dihydroxycholecalciferol is produced in the kidneys, in the proximal tubule cells, from the precursor molecule calcidiol (25-hydroxycholecalciferol), which is produced in the liver from vitamin D3 (formed in the skin).

Question 17

What does calcitonin do to the plasma levels of calcium and phosphate?

Answer 17

It lowers plasma calcium, and lowers plasma phosphate levels.

Question 18

From which cells is calcitonin released?

Answer 18

The parafollicular cells of the thyroid.