Lecture 13: TBL Ca Phosphate Acid Base Flashcards by Serinna Singh

List the major inputs and outputs of calcium and phosphate to and from plasma

Inputs =
GI absorption
Bone restoration

Outputs =
Urinary excretion
Bone mineralization (deposition)

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List the 3 main hormones involved in the regulation of Ca and phosphate, identifying their major site of synthesis

PTH = parathyroid glands

Calcitriol = kidneys

FGF23 = bone

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Describe the effects of PTH on Ca and Pi

Absorption = n/a

Excretion:
Ca = inc. reabsorption in DCT + dec. excretion

Pi = dec. reabsorption in PT + inc. excretion

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Describe effect of calcitriol on Ca and Pi

Excretion = n/a

Absorption = inc. absorption of calcium and phosphate

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Describe effects of FGF23 on Ca and Pi

Absorption = n/a

Excretion = dec. phosphate reabsorption in PT = inc. excretion

No effect on calcium!!

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What are calcitropic hormones?

PTH + calcitriol

Direct relationship with calcium

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What are phosphaturic hormones?

PTH and FGF23

Both have indirect relationship with phosphate

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What do each hormone effect?

PTH = urinary excretion

calcitriol = GI absorption

FGF23 = urinary excretion

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What is a pneumonic for PTH?

PTH

Protects plasma calcium
THwarts phosphate rich diet

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What is PTH’s effect on calcium and phosphate?

Inc. calcium

Dec. phosphate

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What is a pneumonic for calcitriol?

Calcitriol rhymes with skeletal

Provides calcium and phosphate for bone

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What effects does calcitriol have on calcium and phosphate?

Inc. calcium

Inc. phosphate

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What is a pneumonic for FGF23?

ForGet ‘Fosphate’

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What effect does FGF23 have on calcium and phosphate?

Calcium = n/a

Dec. phosphate

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What effects does PTH have on urinary excretion of calcium and phosphate?

Inc. Ca reabsorption in DCT = dec. excretion

Dec. phosphate reabsorption in PT = inc. excretion

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What effect does FGF23 have on phosphate excretion?

Dec. phosphate reabsorption in PT = inc. excretion

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What is the form of calcium that gets regulated??

Ionized!

Does NOT include calcium bound to albumin or complexed with anions

What is the indirect effect of phosphate on PTH secretion?

Inc. phosphate 
=
Dec. ionized calcium
=
Inc. PTH secretion

Explain limitations of using plasma Ca concentration measured by clinical labs when discussing regulation of calcium and phosphate

Clinical labs measure TOTAL plasma calcium = can be misleading!

Inc. phosphate = dec. ionized Ca (but the total Ca would be unchanged)

Total plasma calcium can change even if ionized Ca remains constant
(Ex: if [albumin] changes)

What is the effect of inc. ionized calcium on PTH, calcitriol, FGF23 secretion?

PTH = dec.

Calcitriol = dec.

FGF23 = n/a

What is the effect of inc. phosphate on secretion of PTH, calcitriol and FGF23?

PTH = inc.

Calcitriol = dec.

FGF23 = inc.

What is the effect of dec. plasma calcium on

Calcitriol
Ca IN (GI absorption)
Ca OUT (excretion)
Pi IN (GI absorption)
Pi OUT (excretion)

Dec. plasma Ca =

Inc. calcitriol

Inc. Ca absorption
No change excretion

Inc. Pi absorption
No change excretion

What is the effect of dec. plasma calcium on

PTH
Ca IN (GI absorption)
Ca OUT (excretion)
Pi IN (GI absorption)
Pi OUT (excretion)

Dec. plasma Ca =

Inc. PTH

No change Ca absorption
Dec. Ca excretion

No change Pi absorption
Inc. Pi excretion

What are the effects of inc. plasma phosphate on

Calcitriol
Ca IN (absorption)
Ca OUT (excretion)
Pi IN (absorption)
Pi OUT (excretion)

Inc. plasma phosphate =

Dec. calcitriol

Dec. Ca IN
No change Ca excretion

Dec. Pi IN
No change Pi OUT

What is the effect of increased plasma phosphate on ``` PTH Ca IN (absorption) Ca OUT (excretion) Pi IN (absorption) Pi OUT (excretion) ```

Inc. plasma Pi = Inc. PTH No change Ca IN Dec. Ca excretion No change Pi IN Inc. Pi excretion

What is the effect of increased plasma phosphate on ``` FGF23 Ca IN (absorption) Ca OUT (excretion) Pi IN (absorption) Pi OUT (excretion) ```

Inc. plasma Pi = Inc. FGF23 No change Ca IN No change Ca OUT No change Pi IN Inc. Pi excretion

What are the effects of PTH on secretion of other hormones?

PTH helps the other hormones Inc. calcitriol Inc. FGF23

What are the effects of calcitriol on secretion of other hormones?

calcitriol "calculates": rejects help from PTH but needs FGF to avoid Pi overload Dec. PTH Inc. FGF23

What are the effects of FGF23 on secretion of other hormones?

FGF23 forgets the other hormones Dec. calcitriol Dec. PTH

Describe the two important roles of the kidney in the regulation of acid-base balance

1. Reabsorption of filtered bicarbonate | 2. Synthesis of new bicarbonate

Explain why the kidney cannot eliminate the fixed metabolic acid load by excreting H+ (instead of making 70-100 mmol of new bicarbonate every day)

Kidney can ONLY excrete 0.04 mmol of H+ per day - NOT 70-100 mmol!!!

List the 4 major acid-base disorders

Metabolic acidosis Respiratory acidosis Respiratory alkalosis Metabolic alkalosis

What is a normal level for P(CO2) in mmHg? [HCO3] in mmol/liter?

P(CO2) = 40 [HCO3] = 24

How do you determine type of acid-base disorder?

(1) look at pH - if <7.38 = acidosis - if >7.42 = alkalosis (2) look at P(CO2) Acidosis: - if <40 mmHg = metabolic acidosis - if >40 mmHg = respiratory acidosis Alkalosis: - if <40 mmHg = respiratory alkalosis - if >40 mmHg = metabolic alkalosis

What is the 'rule' to distinguish between acute vs. chronic respiratory acidosis?

If ACUTE: Every 2 mmHg increase in P(CO2) = 0.01 unit dec. in pH

What is the 'rule' to distinguish between acute vs. chronic respiratory alkalosis?

If ACUTE: Every 1 mmHg dec. in P(CO2) = 0.01 unit inc. in pH

Identify important causes of metabolic acidosis

Kidney disease Uncontrolled DM Anaerobic exercise Methanol toxicity CA inhibitors K+-sparing diuretics

Identify important causes of ACUTE respiratory acidosis

Acute opioid or barbiturate OD

Identify important causes of CHRONIC respiratory acidosis

COPD

Identify important causes of ACUTE respiratory ALKalosis

Acute hyperventilation due to anxiety

Identify important causes of chronic respiratory ALKalosis

High altitude | For >48-72 hours

Identify important causes of metabolic alkalosis

Vomiting Hyperaldosteronism Loop diuretics Thiazides diuretics