11/14: Calcium and Phosphorus I

Question 1

What are the 3 main pools within the body that calcium is stored in?

Answer 1

1. Bone
2. Blood/ECF
3. Intracellular calcium

Question 2

What is the normal range for total serum calcium?

Answer 2

8.5-10.5 mg/dL

Question 3

What is the 45% of calcium that is actually biologically active called?

Answer 3

Ionized calcium

Question 4

What is the normal range for ionized calcium?

Answer 4

4.4-5.4 mg/dL

Question 5

Does calcium intake needed increase as you age?

Answer 5

Yes

Question 6

What is the molarity of calcium normally in the interstitial fluid in the extracellular space?

Answer 6

1-2 mM

Question 7

What is the calcium molarity intracellular?

Answer 7

.0001 mM

Question 8

8. Why is this steep gradient needed?

Answer 8

a. It is needed to regulate cell function

Question 9

9. What is phosphorous found as within the body?

Answer 9

a. Inorganic phosphate (Pi)

Question 10

10. Where is the majority of phosphorus found?

Answer 10

In hydroxyapatite of bone and teeth

Question 11

Is the majority of phosphorous absorbed in the gut unlike calcium?

Answer 11

Yes

Question 12

What is the normal adult phosphorosus concentration?

Answer 12

2.5-4.5

Question 13

What are the 4 main organ systems that deal with calcium regulation?

Answer 13

1. Gut
2. Bone
3. Kidney
4. Parathyroid

Question 14

What 3 areas involving these 4 organs deal with the regulation of calcium and phosphorus?

Answer 14

1. Gut absorption
2. Bone turnover
3. Kidney filtration

Question 15

What is net zero Ca and Phosphate balance?

Answer 15

When Ca/Pi ingestion is equal to loss by peeing and pooping

Question 16

What are the 3 key steps involving calcium uptake?

Answer 16

1. Uptake
2. Transcellular transport
3. Extrusion

Question 17

What occurs in uptake of calcium?

Answer 17

Calcium is taking from the apical side of the cell through TRP ion channels

Question 18

What occurs in transcellular transport of calcium?

Answer 18

Calcium once ingested in taken through the cell by calbindin proteins

Question 19

What occurs in extrusion?

Answer 19

Calcium is removed by CaATPase pumps on the basal surface of the cell

Question 20

What transporter takes Pi into the cells within the gut?

Answer 20

NaPi-IIb co-transporter

Question 21

21. Where is this co-transporter located?

Answer 21

a. On the brush border within the ileum

Question 22

22. Why is reabsorption of the kidney so important?

Answer 22

a. Because it gets back up to 90% of Ca and Pi within body

Question 23

23. Are the 3 steps used in gut absorption of Ca the same in the kidney?

Answer 23

Yes

Question 24

24. What differs for Pi absorption in the kidney?

Answer 24

a. A different isoform is used

Question 25

Since the majority of Ca and Pi absorption is similar across organs, how are they altered?

Answer 25

They are altered through hormones that change the expression of the key transporters

Question 26

What are the 3 hormones which regulate calcium?

Answer 26

PTH 1,25-OH2 D3 Calcitonin

Question 27

What are the 3 hormones which regulate phosphate?

Answer 27

PTH 1,25-OH2 D3 Fibroblast growth factor 23 (FGF23)

Question 28

28. Can calcium and phosphate be regulated independently?

Answer 28

Yes

Question 29

29. If calcium is too LOW what happens?

Answer 29

1. Serum Ca decreased 2. PT releases PTH 3. PTH causes i. Bone release of Ca ii. Gut Ca absorption increase iii. Kidney Ca absorption increase 4. Serum Ca restored

Question 30

What occurs if calcium is too HIGH?

Answer 30

1. Serum Ca elevated 2. PT stops releasing PTH 3. PTH decrease causes i. Bone to decrease Ca release ii. Gut to decrease Ca absorption iii. Kidney to decrease Ca reabsorption 4. Serum Ca decreased, homeostasis achieved

Question 31

What protein is expressed by the parathyroid glands to monitor serum calcium?

Answer 31

Calcium sensing receptor (CaSR) i. If calcium to high, CaSR expression increased causing decreased PTH ii. If calcium to low, CaSR expression decreased causing increased PTH

Question 32

What receptor does PTH bind to?

Answer 32

PTH1R

Question 33

33. How does PTH1R and PTH regulate its action?

Answer 33

a. Through the production of cyclic AMP

Question 34

34. What does PTH hormone do to the gut, bone, and kidney?

Answer 34

a. Gut i. Increases Ca resorption b. Bone i. Increases Ca resorption c. Kidney i. Increases Ca reabsorption

Question 35

35. Does PTH have the same effect on the kidney regarding Pi?

Answer 35

No i. PTH causes a reduction in phosphate reabsorption

Question 36

What does PTH do to the active form of Vit. D3?

Answer 36

Cause the conversion of 25 OH D3 to active 1-25 OH2 D3

Question 37

What does 1-25 OH2 D3 do to calcium?

Answer 37

Increases uptake in intestine Increase reabsorption in kidney Increase Ca secretion from bone

Question 38

What does 1-25 OH2 D3 do to Pi?

Answer 38

Increases Pi uptake in intestine Increases Pi resorption in kidney Increases Pi into blood from bone

Question 39

What occurs when calcium is HIGH?

Answer 39

The opposite i. CaSR is activated, resulting in decreased PTH and decreased 1-25 OH2 D3

Question 40

Does calcitonin also help?

Answer 40

Yes, it opposed PTH

Question 41

41. When is calcitonin released?

Answer 41

a. During elevated Ca levels

Question 42

42. How does it do this?

Answer 42

a. Through inhibiting osteoclast resportion through the ruffled border

Question 43

43. Is phosphate regulation as well understood as calcium?

Answer 43

No

Question 44

44. When is FGF23 expressed?

Answer 44

When serum phosphate levels are too high (which occurs when serum calcium levels are too high)

Question 45

What cell expresses it?

Answer 45

Osteocytes

Question 46

What two molecules inhibit the expression of FGF23?

Answer 46

DMP1 PHEX

Question 47

What does FGF23 do in the kidney?

Answer 47

Decrease reabsorption of phosphate by decreasing Na Pi transport expression and decreased 1-25 OH2 D3

Question 48

48. Which are the organ systems is the main regulator of phosphate regulation?

Answer 48

Kidney

Question 49

49. What are the two Na Pi transporters expressed in the kidneys?

Answer 49

NaPiIIa and c