Physiology: Calcium and Phosphate Homeostasis

Question 1

What percentage of Ca is protein bound?

Answer 1

40-45%

Question 2

What percentage of Ca is non-protein bound?

Answer 2

55-60%

Question 3

What percentage of Ca is ionized?

Answer 3

40%

Question 4

What is the only active calcium?

Answer 4

Free ionized Ca

Question 5

What are symptoms of Hypocalcemia?

Answer 5

Tetany
Tingling/numbness
Muscle twitches

Question 6

Normal total calcium?

Answer 6

10 mg/dl

Question 7

Hypocalcemia definition?

Answer 7

<8.5 mg/dl

Question 8

Hypercalcemia definition?

Answer 8

> 10.5 mg/dl

Question 9

Symptoms of hypercalcemia?

Answer 9

Constipation
Polyuria
Polydypsia
Hyporeflexia
Lethargy, coma

Question 10

What happens to Ca in academia?

Answer 10

Hypercalcemia, Ca displaced from ALBUMIN by H

Question 11

What happens to Ca in alkalemia?

Answer 11

Hypocalcemia, H leaves ALBUMIN and Ca binds

Question 12

What three organs effect Ca?

Answer 12

Kidney
Bone
Intestine

Question 13

Where is Ca mostly excreted?

Answer 13

Fecally, then renal is a second

Question 14

Where is PO4 mostly excreted?

Answer 14

Kidney, then fecal is a second

Question 15

What three hormones control Ca?

Answer 15

+: PTH and Vit D

-:Calcitonin

Question 16

What cells in parathyroid make PTH?

Answer 16

Chief cells

Question 17

What cells make Calcitonin? Where?

Answer 17

Parafollicular cells

Thyroid

Question 18

How is vitamin D made?

Answer 18

Skin: UV+7,DHC= Colecalciferol
Liver: 25-Hydroxycholecalciferol
Kidney: 1aHydroxylase makes 1,25HCC
Will make 1,24 HCC if body has high Ca levels

Question 19

What cofactors are required by liver and kidneys to make vitamin D? Difference?

Answer 19

NADPH
O2
Mg
Liver: NO cyp450
Kidney: YES cyp450

Question 20

What binds 25HCC between liver and kidney?

Answer 20

a-globulin

Question 21

What are the causes of HyperPTH?

Answer 21

1*: PTH adenoma

2*: Renal disease (low vit D, hypocalcemia)

Question 22

What is PTH action on bone?

Answer 22

Increase Ca AND PO4

Blasts–>Clasts (bone is initially built, then destroyed)

Question 23

What increases PTH?

Answer 23

Low Ca

Question 24

What receptor is on osteoblasts to start bone resorption? What is it stimulated and inhibited by?

Answer 24

PTHR1–>RANKL–> Clasts
Stim: PTH (Blocks OPG)
Inhibited: Osteoprotegerin (OPG) stim by Estrogen

Question 25

What is PTH action on kidney?

Answer 25

prevent reabsorb PO4 PCT
reabsorb Ca DCT
increase 1a Hydroxylase–>more Vit D3

*kidneys excrete PO4 to allow Ca to be free, since PO4 binds it up and inactivates it

Question 26

What is PTH action on small intestine?

Answer 26

Indirect: increased Vit D3 from renal 1aHydroxylase promotes Ca absorption

Question 27

What is the effect of calcitonin?

Answer 27

Excrete Ca, lower Ca, lower bone uptake

Opposite of PTH, except is also increases PO4 excretion.

Question 28

What is the effect of Vit D on intestine?

Answer 28

Calbindin D-28K increase uptake in Ca/PO4

Ca/ATPase

Question 29

What is the effect of Vit D on the kidney?

Answer 29

Resorption of Ca AND PO4 (unlike PTH, which excretes PO4!)

Question 30

What is the effect of Vit D on bone?

Answer 30

Osteoclast increase

Increase Ca/PO4 to increase mineralization materials

Question 31

What is the formula for true calcium?

Answer 31

True Ca=Measured Ca + 0.8(4-albumin)

Question 32

Cortisol does what to bone?

Answer 32

Osteoporosis

Question 33

What is the normal amount of PO4?

Answer 33

4mg/dl

Question 34

What does renal failure do to PO4? Ca?

Answer 34

PO4: Hyperphosphatemia
Ca: Hypocalcemia

Question 35

What does FGF23 do?

Answer 35

Negative feedback:
Decrease PTH/VitD/PO4
Via: Incrase in Na/P cotransporter synthesis