Calcium and Phosphate Metabolism

Question 1

What are the most important hormones in calcium metabolism?

Answer 1

Ca2+
Parathyroid hormone
1,25(OH)2D (calciferol)

Question 2

What are the most important organs for Ca2+ metabolism?

Answer 2

• Intestine
• Bone
• Kidney
• Parathyroid gland

Question 3

Parathyroid hormone is produced in the ____ cells of the parathyroid gland

Answer 3

Chief

Question 4

What are the two negative feedback loops that influence parathyroid hormone secretion?

Answer 4

• Serum ionized calcium

- Serum 1,25 dihydroxyvitamin D

Question 5

How is renal tubular calcium handling regulated?

Answer 5

CaR

Question 6

What is the best indicator of vitamin D status?

Answer 6

Calcidiol

Question 7

What is the role of parathyroid hormone-related peptide (PTHrP) ?

Answer 7

Paracrine regulator of breast, skin and bone development

Question 8

What is the most common cause of cancer-associated hypercalcaemia?

Answer 8

PTHrP production by tumours

Question 9

Diagnosis of PTH dependent hypercalcemia requires ____ Ca2+ and ___ PTH

Answer 9

Elevated Ca2+

Increased PTH

Question 10

Diagnosis of PTH independent hypercalcemia requires ____ Ca2+ and ___ PTH

Answer 10

Elevated Ca2+

Decreased PTH

Question 11

How can cancer cause PTH independent hypercalcemia?

Answer 11

• PTHrP
• Extensive lytic bone disease
• Tumoral expression of 1-alpha hydroxylase -> 1,25 dihydroxyvitaminD

Question 12

Why can sarcoidosis cause PTH independent hypercalcemia?

Answer 12

Granulomatous tissue can convert 25(OH)D -> 1,25(OH)2D

Question 13

What is the most common cause of hypoparathyroidism?

Answer 13

Post surgical/post neck irradiation

Question 14

What are the two most common abnormalities of vitamin D metabolism?

Answer 14

Vitamin D deficiency and renal failure

Question 15

What are the main hormones involved in phosphate metabolism?

Answer 15

Vitamin D, PTH and phosphatonins

Question 16

PTH ____ renal excretion of phosphate

Answer 16

Stimulates

Question 17

Calcitrol ____ intestinal absorption of phosphate and _____ urinary phosphate excretion

Answer 17

Increases

Decreases

Question 18

Phosphatonins _____ urinary phosphate secretion

Answer 18

Increase

Question 19

What is the most important phosphatonin in phosphate regulation?

Answer 19

FGF-23

Question 20

Why do very sick patients often have moderately low phosphates?

Answer 20

Respiratory alkalosis changes pH -> causes movement of phosphate from ECF to ICF

Question 21

What is the main source of phosphatonins in the body?

Answer 21

Skeleton

Question 22

What is the mechanism of FGF23?

Answer 22

• Inhibit production of phosphate transporting proteins in the renal tubule
• Inhibit 1-alpha hydroxylase enzyme

Question 23

What is the mechanism of Fanconi syndrome?

Answer 23

Global deficiency in phosphate transport -> hypophosphatemia