Renal Control Of Acid-Base Balance Flashcards
Normal range of pH values
7.35 to 7.45
Condition in which H+ concentration in BLOOD is increased (decreased pH)
Acidemia
Condition in which H+ ion concentration in blood is decreased (increased pH)
Alkalemia
Excessively acidic condition of body fluids or tissues with a pH less than 7.35
Acidosis
Excessively alkaline condition of body fluids or tissues with a pH of greater than 7.45
Alkalosis
Major chemical buffer systems in the body
Bicarbonate (pK = 6.1)
Hemoglobin (pK = 7.3)
Phosphate (pK = 6.8)
Plasma proteins (pK = 6.7)
Mechanism of buffering in the kidneys
Bicarbonate reabsorption and regeneration
Ammonia formation
Phosphate buffering
Henderson-Hasselbach equation as it applies to CO2:HCO3 buffer system
pH = 6.1 + log([HCO3-]/[H2CO3])
Sources of volatile (CO2 derived) acids and mechanism for eliminating
Glucose (produces H+, bicarb, and/or lactate)
Fat (produces H+ and bicarb)
Eliminated by the lungs
Sources of nonvolatile acids and mechanism for eliminating
Cysteine (produces H+ and sulfate)
Phosphoprotein (produces H+ and phosphate)
Eliminated by the kidneys
A 0.3 decrease in pH does what to the H+ concentration?
Doubles it
A 0.3 increase in pH does what to the H+ concentration?
Halves it
What occurs with ammoniagenesis and net acid secretion during hypokalemia?
Both increase
Would the following result in increased or decreased H+ secretion:
Increase in ECF volume
Decrease in aldosterone
Hyperkalemia
Decrease in filtered load of HCO3
Decreased H+ secretion
Would an increase in partial pressure of arterial CO2 result in an increased or decreased H+ secretion?
Increased
Role of alpha vs. beta cells in the CCD in bicarbonate metabolism
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]
Net acid excretion equation must equal __________ ______ production each day in order to maintain acid-base balance
Nonvolatile acid
What are the 2 primary urinary buffers?
Titratable acid
Ammonium excretion
[thus fixed H+ can be excreted as titratable acid such as H2PO4 or as NH4+]
_____ _____ are salts of primarily phosphate, but other constituents of urine such as creatinine may contribute; accounts for about 1/3 of net acid excretion
Titratable acids
If titratable acids account for 1/3 of net acid excretion, what accounts for the other 1/3?
Ammonium synthesis and secretion
[note that body can make as much ammonium as it needs, unlike titratable acids]
Adjustments in filtered load and reabsorption of HCO3 in metabolic acidosis
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?]
Adjustments in filtered load and reabsorption of HCO3 in metabolic alkalosis
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]
Changes in extracellular pH with Conn’s disease
Conn’s disease = hyperaldosteronism
Retain Na, excrete K+ –> ECF volume expansion with hypokalemia and risk for alkalosis (extracellular pH increase)
Changes in extracellular pH with Addison’s disease
Addison’s = lack of aldosterone/corticosteroids
Excrete Na, retain K+ –> ECF volume contraction with hyperkalemia and risk for acidosis (extracellular pH decrease)
Changes in extracellular pH with diuretic abuse
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
Anion gap calculation
Na - (Cl + HCO3)
Normal = 8-12 (note: previously learned 6-12 as normal)
(Urine anion gap = Na + K - Cl, should be about 8)
How to tell if respiratory acidosis is acute or chronic
If acute:
Expected HCO3 = 24 + ((PaCO2-40)/10)
If chronic:
Expected HCO3 = 24 + 4((PaCO2-40)/10)
How to tell if respiratory alkalosis is acute or chronic
If acute:
Expected HCO3 = 24 - 2((PaCO2-40)/10)
If chronic:
Expected HCO3 = 24 - 5((PaCO2-40)/10)
How to determine if metabolic alkalosis is Cl-responsive or Cl-unresponsive
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.)
Which of the following usually results in a negative urine anion gap?
A. Metabolic acidosis
B. Metabolic alkalosis
C. Respiratory acidosis
D. Respiratory alkalosis
A. Metabolic acidosis
Since NH4 excretion increases with generation of “new” bicarb
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 ________
Reabsorption; excreted
ECF volume expansion results in ______ HCO3 reabsorption
ECF volume contraction results in _______ HCO3 reabsorption
Decreased
Increased (known as contraction alkalosis)
What role does angiotensin II play in renal acid-base physiology?
Stimulates Na/H exchange and thus increases HCO3 reabsorption, contributing to the contraction alkalosis secondary to ECF volume contraction
The amount of H+ excreted as titratable acid depends on what 2 things?
Amount of urinary buffer
pK of the buffer
The amount of H+ excreted as NH4+ depends on what 2 factors?
Amount of NH3 synthesized by renal cells
Urine pH
Which of the following is most likely to cause metabolic alkalosis?
A. Vomiting B. Diarrhea C. Chronic renal failure D. Salicylate intoxication E. COPD
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.]
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?
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)
In which of the following might symptoms of hypocalcemia occur?
A. Metabolic acidosis
B. Metabolic alkalosis
C. Respiratory acidosis
D. Respiratory alkalosis
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]
