Renal Control Of Acid-Base Balance

Question 1

Normal range of pH values

Answer 1

7.35 to 7.45

Question 2

Condition in which H+ concentration in BLOOD is increased (decreased pH)

Answer 2

Acidemia

Question 3

Condition in which H+ ion concentration in blood is decreased (increased pH)

Answer 3

Alkalemia

Question 4

Excessively acidic condition of body fluids or tissues with a pH less than 7.35

Answer 4

Acidosis

Question 5

Excessively alkaline condition of body fluids or tissues with a pH of greater than 7.45

Answer 5

Alkalosis

Question 6

Major chemical buffer systems in the body

Answer 6

Bicarbonate (pK = 6.1)

Hemoglobin (pK = 7.3)

Phosphate (pK = 6.8)

Plasma proteins (pK = 6.7)

Question 7

Mechanism of buffering in the kidneys

Answer 7

Bicarbonate reabsorption and regeneration

Ammonia formation

Phosphate buffering

Question 8

Henderson-Hasselbach equation as it applies to CO2:HCO3 buffer system

Answer 8

pH = 6.1 + log([HCO3-]/[H2CO3])

Question 9

Sources of volatile (CO2 derived) acids and mechanism for eliminating

Answer 9

Glucose (produces H+, bicarb, and/or lactate)

Fat (produces H+ and bicarb)

Eliminated by the lungs

Question 10

Sources of nonvolatile acids and mechanism for eliminating

Answer 10

Cysteine (produces H+ and sulfate)

Phosphoprotein (produces H+ and phosphate)

Eliminated by the kidneys

Question 11

A 0.3 decrease in pH does what to the H+ concentration?

Answer 11

Doubles it

Question 12

A 0.3 increase in pH does what to the H+ concentration?

Answer 12

Halves it

Question 13

What occurs with ammoniagenesis and net acid secretion during hypokalemia?

Answer 13

Both increase

Question 14

Would the following result in increased or decreased H+ secretion:

Increase in ECF volume
Decrease in aldosterone
Hyperkalemia
Decrease in filtered load of HCO3

Answer 14

Decreased H+ secretion

Question 15

Would an increase in partial pressure of arterial CO2 result in an increased or decreased H+ secretion?

Answer 15

Increased

Question 16

Role of alpha vs. beta cells in the CCD in bicarbonate metabolism

Answer 16

Alpha-IC cells of CCD reabsorb bicarb (H+ secreted)

Beta-IC cells of CCD secrete bicarb (H+ reabsorbed)

[“New” bicarb is generated during process of urine acidification when secreted H+ is buffered for excretion, while bicarb is reabsorbed by alpha cells]

Question 17

Net acid excretion equation must equal __________ ______ production each day in order to maintain acid-base balance

Answer 17

Nonvolatile acid

Question 18

What are the 2 primary urinary buffers?

Answer 18

Titratable acid

Ammonium excretion

[thus fixed H+ can be excreted as titratable acid such as H2PO4 or as NH4+]

Question 19

_____ _____ are salts of primarily phosphate, but other constituents of urine such as creatinine may contribute; accounts for about 1/3 of net acid excretion

Answer 19

Titratable acids

Question 20

If titratable acids account for 1/3 of net acid excretion, what accounts for the other 1/3?

Answer 20

Ammonium synthesis and secretion

[note that body can make as much ammonium as it needs, unlike titratable acids]

Question 21

Adjustments in filtered load and reabsorption of HCO3 in metabolic acidosis

Answer 21

A decreased serum pH may be corrected by the kidneys by increasing acid titration, increasing acid excretion in urine and increasing bicarb regeneration in the nephron

[filtered load of HCO3 decreases?]

Question 22

Adjustments in filtered load and reabsorption of HCO3 in metabolic alkalosis

Answer 22

With an increased serum pH, kidney does 2 things:

Decreased tubular reabsorption of bicarb

Decreased acid titration –> decreased acid excretion and decreased bicarb regeneration

[in metabolic alkalosis, the increased bicarb level will result in increased filtration of bicarb, provided the GFR has not decreased = Filtered load is high]

Question 23

Changes in extracellular pH with Conn’s disease

Answer 23

Conn’s disease = hyperaldosteronism

Retain Na, excrete K+ –> ECF volume expansion with hypokalemia and risk for alkalosis (extracellular pH increase)

Question 24

Changes in extracellular pH with Addison’s disease

Answer 24

Addison’s = lack of aldosterone/corticosteroids

Excrete Na, retain K+ –> ECF volume contraction with hyperkalemia and risk for acidosis (extracellular pH decrease)

Question 25

Changes in extracellular pH with diuretic abuse

Answer 25

With loop and thiazide diuretics acting upstream of CCD, K+ is lost –> hypokalemia + metabolic alkalosis

K-sparing diuretics (and drugs that inhibit RAS) –> hyperkalemia + metabolic acidosis

Question 26

Anion gap calculation

Answer 26

Na - (Cl + HCO3)

Normal = 8-12 (note: previously learned 6-12 as normal)

(Urine anion gap = Na + K - Cl, should be about 8)

Question 27

How to tell if respiratory acidosis is acute or chronic

Answer 27

If acute:
Expected HCO3 = 24 + ((PaCO2-40)/10)

If chronic:
Expected HCO3 = 24 + 4((PaCO2-40)/10)

Question 28

How to tell if respiratory alkalosis is acute or chronic

Answer 28

If acute:
Expected HCO3 = 24 - 2((PaCO2-40)/10)

If chronic:
Expected HCO3 = 24 - 5((PaCO2-40)/10)

Question 29

How to determine if metabolic alkalosis is Cl-responsive or Cl-unresponsive

Answer 29

If Cl-responsive, urine Cl- will be <20 mEq/L

If Cl-unresponsive, urine Cl- will be >20 mEq/L and hypokalemic (caused by hyperaldosteronism, K+ losing diuretics, etc.)

Question 30

Which of the following usually results in a negative urine anion gap?

A. Metabolic acidosis
B. Metabolic alkalosis
C. Respiratory acidosis
D. Respiratory alkalosis

Answer 30

A. Metabolic acidosis

Since NH4 excretion increases with generation of “new” bicarb

Question 31

Increases in the filtered load of HCO3 result in increased rates of HCO3 __________. However, if the plasma HCO3 concentration becomes very high (e.g., metabolic alkalosis), the filtered load will exceed the reabsorptive capacity, and HCO3 will be ________

Answer 31

Reabsorption; excreted

Question 32

ECF volume expansion results in ______ HCO3 reabsorption

ECF volume contraction results in _______ HCO3 reabsorption

Answer 32

Decreased

Increased (known as contraction alkalosis)

Question 33

What role does angiotensin II play in renal acid-base physiology?

Answer 33

Stimulates Na/H exchange and thus increases HCO3 reabsorption, contributing to the contraction alkalosis secondary to ECF volume contraction

Question 34

The amount of H+ excreted as titratable acid depends on what 2 things?

Answer 34

Amount of urinary buffer

pK of the buffer

Question 35

The amount of H+ excreted as NH4+ depends on what 2 factors?

Answer 35

Amount of NH3 synthesized by renal cells

Urine pH

Question 36

Which of the following is most likely to cause metabolic alkalosis?

A. Vomiting
B. Diarrhea
C. Chronic renal failure
D. Salicylate intoxication
E. COPD

Answer 36

A. Vomiting

[vomiting causes loss of gastric H+, leaving HCO3 behind in the blood. Diarrhea cauaes GI loss of HCO3 leading to metabolic acidosis. Chronic renal failure and salicylate intoxication also cause metabolic acidosis. Salicylate intoxication also causes respiratory alkalosis. COPD causes respiratory acidosis.]

Question 37

In metabolic acidosis, the concentration of an ion other than HCO3 must increase to replace it as it is depleted in buffering process. The anion can be Cl or an unmeasured ion. How would these 2 options change the anion gap?

Answer 37

The serum anion gap is increased in concentration of unmeasured anion is increased to replace HCO3

The serum anion gap is normal if concentration of Cl is increased to replace HCO3 (hyperchloremic metabolic acidosis)

Question 38

In which of the following might symptoms of hypocalcemia occur?

A. Metabolic acidosis
B. Metabolic alkalosis
C. Respiratory acidosis
D. Respiratory alkalosis

Answer 38

D. Respiratory alkalosis

[H and Ca compete for binding sites on plasma proteins. Decreased H+ causes increased protein binding of Ca and decreased free ionized Ca]