Calcium and Phosphorous metabolism 4/ 20/13

Question 1

85% of phosphorous is found where>

Answer 1

Bone

Question 2

What does CKD-BMD stand for?

Answer 2

Chronic Kidney Disease- Bone Mineral Disorder

Question 3

Where is most phosphorous reabsorbed?

Answer 3

Proximal Conv Tubule…NaPi transporter

Question 4

Describe the renal handling of phosphate in regards to its Threshold (TmP)

Answer 4

The tubular reabsorption of phosphate is saturable, If GFR stays above 40, the TmP varies proportionately with GFR. If GFR drops below 40, the Tmp doesn’t change in proportion anymore and you get hyperphosphatemia

Question 5

What is the main stimulator for PTH production>

Answer 5

Hypocalcemia

Question 6

Physiologically, how does PTH work in the kidney, gut, and bone.

Answer 6

PTH generally increases 1,25 dihydroxy D (Calcitrol…the hormonally active form of vit D) levels which leads to more calcium reabsorption in the intestines and more bone turnover leading to calcium in the blood, less phosphorous reabsorption. In the gut, both phosphorous and vit. D go up.

Question 7

What happens in CKD

Answer 7

Phosphate levels rise b/c kidney isn’t working which means that Calcitrol is not being produced to stimulate Vit D uptake in the intestines and phosphate removal

Question 8

Clinical hyperphosphatemia occurs at a GFR around what?

Answer 8

40

Question 9

Hyperphosphatemia has what effect on vascular smooth muscle cells?

Answer 9

calcification

Question 10

How much Calcium is taken in per day?

Answer 10

1000 mg, kidney must excrete 300 mg

Question 11

Hormonaly active Vitamin D is made where?

Answer 11

Kidney

Question 12

What effect does calcitrol have on the NaPi cotransporter

Answer 12

disables it so less Na and Phosphorous come into the cell.

Question 13

What stimulates the production of calcitrol

Answer 13

PTH

Question 14

Less phosphorous reabsorption leads to what effect on calcium reabsorption?

Answer 14

Goes up

Question 15

Risk of hypo and hypercalcemia both worsen with CKD?

Answer 15

Yes

Question 16

What does serum calcium measure?

Answer 16

unbound calcium…40% of it is bound unfortunately This makes it difficult to measure true serum calcium

Question 17

Hypercalcemia is a strong indicator of mortality?

Answer 17

Yes

Question 18

Hypocalcemia leads to what?

Answer 18

Increased neuromuscular activity

Question 19

Hypercalcemia leads to what?

Answer 19

CV and soft tissue calcification

Question 20

Patients with CKD often have this triad of lab values regarding phosphorous, Calcium, and PTH

Answer 20

High Phosphorous, low calcium, high PTH. All interconnected. the low ca and high P cause higher pTH

Question 21

FGF 23 is what?

Answer 21

Heparin independent endocrine factor that stimulates phosphorous and vitamin D homeostasis

Question 22

FGF 23 excess associated with what?

Answer 22

Low serum phosphate…rickets, Low vit D osteomalacia

Question 23

High FGF 23

Answer 23

soft tissue calcification

Question 24

Where is FGF 23 produced?

Answer 24

Bone