A 65-year-old man with COPD has chronic CO2 retention. His kidneys gradually increase H+ secretion and HCO3- reabsorption. Which mechanism best explains this response?
A. Type A cells inhibited
B. NH4+ excretion reduced
C. Alveolar CA activated
D. ↑Proximal Na+-H+ countertransport

D. ↑Proximal Na+-H+ countertransport

A patient with severe diarrhea develops metabolic acidosis. Which parameter is most likely decreased?
A. Plasma HCO3- level
B. Plasma H+ level
C. Plasma PCO2 level
D. Urine NH4+ excretion

A. Plasma HCO3- level

An emphysematous patient is somnolent. ABG: pH 7.28, PCO2 60, HCO3- 27. Best diagnosis?
A. Metabolic acidosis
B. Respiratory acidosis
C. Metabolic alkalosis
D. Respiratory alkalosis

B. Respiratory acidosis

In metabolic acidosis, Kussmaul breathing occurs primarily to:
A. Decrease renal H+ excretion
B. Increase renal HCO3 formation
C. Increase tissue O2 extraction
D. Lower PCO2, reduce H+

D. Lower PCO2, reduce H+

Hyperventilation during high-altitude exposure most directly causes:
A. Respiratory alkalosis
B. Metabolic acidosis
C. Respiratory acidosis
D. Metabolic alkalosis

A. Respiratory alkalosis

A patient with Conn syndrome develops metabolic alkalosis. Which finding supports the diagnosis?
A. ↓Aldosterone activity
B. ↓HCO3- reabsorption
C. ↑H+ secretion, intercalated
D. Hyperkalemic acidosis

C. ↑H+ secretion, intercalated

In diabetic ketoacidosis, the elevated anion gap is primarily due to:
A. Chloride accumulation
B. Unmeasured anions, ketoacids
C. Increased plasma sodium
D. Decreased albumin

B. Unmeasured anions, ketoacids

Which buffering system plays the major role inside red blood cells?
A. Phosphate buffer
B. Hemoglobin buffer
C. Ammonia buffer
D. Bicarbonate buffer

B. Hemoglobin buffer

In chronic renal failure, metabolic acidosis develops mainly because:
A. Lungs cannot excrete CO2
B. Aldosterone excess persists
C. Nonvolatile acids accumulate
D. HCO3- reabsorption increases

C. Nonvolatile acids accumulate

A patient with prolonged vomiting develops hypochloremic metabolic alkalosis. Primary mechanism?
A. Loss of gastric acid
B. Loss of GI bicarbonate
C. Decreased aldosterone
D. Retained gastric acid

A. Loss of gastric acid

Which is a primary cause of respiratory acidosis?
A. High-altitude exposure
B. CNS depression
C. Severe anxiety
D. Salicylate poisoning

B. CNS depression

What is the renal response to sustained respiratory acidosis?
A. ↓Renal NH4+ synthesis
B. ↓H+ secretion
C. ↑Titratable acid excretion
D. ↑Plasma chloride

C. ↑Titratable acid excretion

Which buffer system is especially important for acid excretion in the distal nephron?
A. Hemoglobin buffer
B. Carbonate buffer
C. Phosphate buffer
D. Protein buffer

C. Phosphate buffer

In metabolic alkalosis due to diuretic therapy, which secondary change is expected?
A. Hyperventilation
B. ↓PCO2
C. ↑Renal H+ secretion
D. Hypoventilation

D. Hypoventilation

The phosphate buffer pK (6.8) makes it ideal for buffering:
A. Intracellular, tubular fluid
B. Arterial blood
C. Interstitial fluid
D. Venous blood

A. Intracellular, tubular fluid

Which renal process produces a “new” bicarbonate ion?
A. H+ binds phosphate/ammonia
B. Glomerular HCO3- filtration
C. Na+-HCO3- reabsorption
D. Passive CO2 diffusion

A. H+ binds phosphate/ammonia

Which hormone stimulates H+ secretion in cortical collecting ducts?
A. Parathyroid hormone
B. Aldosterone
C. Vasopressin
D. Angiotensin II

B. Aldosterone

Chronic metabolic acidosis increases excretion of:
A. HCO3-
B. Cl-
C. NH4+
D. Na+

C. NH4+

Salicylate overdose presents early with respiratory alkalosis primarily due to:
A. Carbonic anhydrase inhibition
B. Bicarbonate loss
C. CNS respiratory stimulation
D. Peripheral chemoreceptor suppression

C. CNS respiratory stimulation

Which would decrease renal H+ secretion?
A. Increased angiotensin II
B. Elevated aldosterone
C. Hyperkalemia
D. Volume depletion

C. Hyperkalemia

A patient develops severe diarrhea. Which acid–base abnormality is most likely?
A. Respiratory alkalosis
B. Metabolic acidosis
C. Respiratory acidosis
D. Metabolic alkalosis

B. Metabolic acidosis

Which enzyme catalyzes carbonic acid formation in renal tubular cells?
A. Carbonic anhydrase
B. Aldolase
C. ATP synthase
D. Phosphofructokinase

A. Carbonic anhydrase

In metabolic acidosis, renal compensatory responses include:
A. ↑H+ secretion, new HCO3-
B. ↓NH4+ excretion
C. ↓Phosphate buffering
D. ↓Ammoniagenesis

A. ↑H+ secretion, new HCO3-

ABG: pH 7.49, PCO2 50, HCO3- 36. Best diagnosis?
A. Mixed alkalosis
B. Metabolic alkalosis
C. Respiratory alkalosis
D. Normal acid–base

B. Metabolic alkalosis

Fanconi syndrome primarily causes:
A. ↓HCO3- reabsorption
B. ↑HCO3- reabsorption
C. ↑Phosphate reabsorption
D. ↓K+ secretion

A. ↓HCO3- reabsorption

Lactic acidosis with an anion gap of 24 suggests:
A. Unmeasured anion accumulation
B. Hypoalbuminemia
C. Excess chloride retention
D. Diarrheal bicarbonate loss

A. Unmeasured anion accumulation

How are ammonium ions “trapped” in urine?
A. NH4+ diffuses luminally
B. NH3 + H+ → NH4+
C. NH4+ pumped by ATPase
D. NH4+ exchanges with Cl-

B. NH3 + H+ → NH4+

"Hyperchloremic metabolic acidosis” is best defined as:
A. Increased unmeasured anions
B. Cl- rises as HCO3- falls
C. Hypochloremic alkalosis
D. Respiratory acidosis with chloride

B. Cl- rises as HCO3- falls

Renal tubular acidosis is best described as:
A. Lung failure to excrete CO2
B. Excess aldosterone effect
C. Tubular H+ or HCO3- defect
D. Increased protein buffering

C. Tubular H+ or HCO3- defect

IV ammonium chloride is given to treat alkalosis. Physiologic effect?
A. Neutralizes plasma H+
B. Suppresses renal acid excretion
C. Liver urea cycle releases HCl
D. Converts to CO2, H2O

C. Liver urea cycle releases HCl

A diabetic patient has pH 7.29, HCO3- 12, PCO2 24. Best description?
A. Normal acid–base
B. Mixed alkalosis
C. Respiratory acidosis
D. Metabolic acidosis

D. Metabolic acidosis

In metabolic acidosis, which change helps restore pH?
A. ↓Alveolar ventilation
B. ↑Plasma PCO2
C. ↑Alveolar ventilation
D. ↓Renal H+ secretion

C. ↑Alveolar ventilation

Vomiting of intestinal contents causes metabolic acidosis because of:
A. Loss of intestinal bicarbonate
B. Increased aldosterone secretion
C. Loss of hydrochloric acid
D. Impaired H+ secretion

A. Loss of intestinal bicarbonate

Which compensatory mechanism occurs in respiratory alkalosis?
A. ↓Renal H⁺ secretion and ↓HCO₃⁻ reabsorption
B. Increased ventilation
C. ↑Renal acid excretion
D. ↑Carbonic anhydrase activity

A. ↓Renal H⁺ secretion and ↓HCO₃⁻ reabsorption

In chronic metabolic acidosis, renal ammonium excretion increases up to:
A. 500 mEq/day
B. 100 mEq/day
C. 200 mEq/day
D. 1000 mEq/day

A. 500 mEq/day

The renal response to metabolic alkalosis is to:
A. ↑H+ secretion
B. ↑NH4+ production
C. ↓H+ secretion, excrete HCO3-
D. ↑HCO3- reabsorption

C. ↓H+ secretion, excrete HCO3-

Which abnormality is most likely with hyperaldosteronism?
A. Hypernatremic acidosis
B. Hypokalemic alkalosis
C. Hyponatremic acidosis
D. Hyperkalemic acidosis

B. Hypokalemic alkalosis

In COPD-related respiratory acidosis, which values are expected?
A. ↓PCO2, ↑pH
B. ↑HCO3-, ↑pH
C. ↓HCO3-, ↑pH
D. ↑PCO2, ↓pH

D. ↑PCO2, ↓pH

Which statement best describes how kidneys respond to respiratory acidosis?
A. ↑H+ secretion, new HCO3-
B. ↓HCO3- reabsorption
C. ↓NH4+ excretion
D. ↑Urinary pH

A. ↑H+ secretion, new HCO3-

What is the effect of carbonic anhydrase inhibition on acid–base balance?
A. No net acid–base change
B. ↑H+ secretion, alkalosis
C. ↑HCO3- reabs, alkalosis
D. ↓HCO3- reabs, acidosis

D. ↓HCO3- reabs, acidosis

A patient with severe lactic acidosis would most likely show:
A. Decreased anion gap
B. Normal anion gap
C. Increased anion gap
D. Increased plasma chloride

C. Increased anion gap

Which condition most commonly causes normal anion gap metabolic acidosis?
A. Diarrhea
B. Methanol poisoning
C. Ketoacidosis
D. Lactic acidosis

A. Diarrhea

Which is the most powerful acid–base regulatory system?
A. Protein buffer
B. Respiratory center
C. Kidneys
D. Bicarbonate buffer

C. Kidneys

ABG: pH 7.55, PCO2 30, HCO3- 22. Which value is primarily driving alkalemia?
A. Elevated HCO3-
B. Elevated PCO2
C. Decreased HCO3-
D. Decreased PCO2

D. Decreased PCO2

“New” bicarbonate is added to plasma when:
A. Aldosterone decreases
B. Filtered HCO3- reabsorbs
C. H+ binds phosphate/ammonia
D. Unbuffered H+ excretes

C. H+ binds phosphate/ammonia

Which would produce respiratory acidosis?
A. Anxiety hyperventilation
B. High-altitude ascent
C. Carbonic anhydrase inhibition
D. Airway obstruction

D. Airway obstruction

Why is the bicarbonate buffer effective despite pK 6.1?
A. Acts only intracellularly
B. CO2 and HCO3- regulated
C. Concentrated inside RBCs
D. Minimal buffering required

B. CO2 and HCO3- regulated

In metabolic acidosis, respiratory compensation begins in:
A. Minutes
B. Days
C. Seconds
D. Hours

A. Minutes

Which finding differentiates metabolic alkalosis from respiratory alkalosis?
A. Decreased PCO2
B. Decreased plasma pH
C. Increased plasma HCO3-
D. Normal HCO3-

C. Increased plasma HCO3-

During chronic acidosis, urinary ammonium excretion:
A. Decreases below normal
B. Increases dramatically
C. Converts to urea, retained
D. Remains unchanged

B. Increases dramatically

Which of the following is a cause of metabolic alkalosis?
A. Loop diuretics
B. Chronic renal failure
C. Severe diarrhea
D. Emphysema

A. Loop diuretics

ABG: pH 7.31, PCO2 45, HCO3- 22. Primary disturbance is:
A. Metabolic acidosis
B. Respiratory acidosis
C. Respiratory alkalosis
D. Metabolic alkalosis

B. Respiratory acidosis

Which lab finding suggests compensation in respiratory acidosis?
A. Decreased plasma bicarbonate
B. Increased plasma bicarbonate
C. Increased plasma chloride
D. Decreased plasma PCO2

B. Increased plasma bicarbonate

Major nonvolatile acids requiring renal excretion are:
A. Carbonic acid
B. Sulfuric and phosphoric acids
C. Lactic acid
D. Nitric acid

B. Sulfuric and phosphoric acids

A “mixed” acid–base disorder means:
A. Compensation is complete
B. Only one system acts
C. Metabolic and respiratory exclude
D. Two primary disorders coexist

D. Two primary disorders coexist

In Addison disease (low aldosterone), expected acid–base disturbance:
A. Respiratory alkalosis
B. Metabolic acidosis
C. Metabolic alkalosis
D. Respiratory acidosis

B. Metabolic acidosis

After rapid ascent to high altitude, the earliest arterial change is:
A. Increased HCO3-
B. Increased chloride
C. Increased PCO2
D. Decreased PCO2

D. Decreased PCO2

Immediate buffer response to sudden extracellular H+ increase:
A. Increased renal H+ secretion
B. Decreased CO2 production
C. Increased NH4+ formation
D. ↑H+ binding to buffers

D. ↑H+ binding to buffers

COPD patient receives high-flow O2 and retains CO2. Acid–base change?
A. Mixed metabolic acidosis
B. Respiratory alkalosis
C. Metabolic alkalosis
D. Respiratory acidosis

D. Respiratory acidosis

Most appropriate immediate therapy for severe metabolic acidosis:
A. Oral NH4Cl
B. Fluid restriction
C. IV sodium bicarbonate
D. Beta-agonists

C. IV sodium bicarbonate

Which renal process prevents bicarbonate loss without creating “new” bicarbonate?
A. Reabsorb filtered HCO3-
B. Excrete unbuffered H+
C. Secrete H+ to ammonia
D. Secrete H+ to phosphate

A. Reabsorb filtered HCO3-

After days of respiratory alkalosis, kidneys primarily:
A. Increase NH4+ excretion
B. Increase H+ secretion
C. Increase HCO3- reabs
D. Decrease HCO3- reabs

D. Decrease HCO3- reabs

The pK of the bicarbonate buffer system is:
A. 7.4
B. 6.1
C. 6.8
D. 5.6

B. 6.1

In hypochloremic metabolic alkalosis from vomiting, which plasma change is expected?
A. Decreased chloride
B. Increased chloride
C. Decreased sodium
D. Increased phosphate

A. Decreased chloride

Hyperchloremic metabolic acidosis typically features a:
A. Decreased anion gap
B. Increased anion gap
C. Negative anion gap
D. Normal anion gap

D. Normal anion gap

Diabetic ketoacidosis classically produces:
A. Normal gap alkalosis
B. Normal gap acidosis
C. High gap alkalosis
D. High gap acidosis

D. High gap acidosis

For ammonium trapping, which species diffuses most readily into tubular lumen?
A. NH4+
B. NH3
C. HCO3-
D. Cl-

B. NH3

Salicylate toxicity classically presents as:
A. Respiratory acidosis only
B. Metabolic alkalosis only
C. Mixed alkalosis
D. Metabolic acidosis + resp alkalosis

D. Metabolic acidosis + resp alkalosis

Respiratory compensation for metabolic alkalosis tends to:
A. Decrease HCO3-
B. Decrease chloride
C. Decrease PCO2
D. Increase PCO2

D. Increase PCO2

In hyperchloremic metabolic acidosis, plasma chloride is usually:
A. Decreased
B. Unchanged
C. Increased
D. Undetectable

C. Increased