COMSAE PHASE 1 GENERAL PHYSIOLOGY
PRACTICE EXAM WITH ACTUAL
QUESTIONS AND VERIFIED ANSWERS,
PLUS EXPLAINED RATIONALES/EXPERT
VERIFIED FOR GUARANTEED 100% PASS
2026/LATEST UPDATE/INSTANT
DOWNLOAD PDF
Question 1
A 24-year-old healthy man undergoes an experimental study of renal
physiology. His plasma sodium concentration is 140 mEq/L, and his
extracellular fluid volume is normal. Researchers administer a substance
that selectively increases the permeability of the collecting duct to water
without directly changing sodium transport. Which change would most
directly occur as a result?
A. Increased intracellular sodium concentration in collecting duct
principal cells
B. Increased water reabsorption from the tubular lumen
C. Decreased medullary interstitial osmolality
D. Increased renal plasma flow
E. Decreased glomerular filtration rate
Answer: B. Increased water reabsorption from the tubular lumen
Rationale: Antidiuretic hormone increases water permeability of
principal cells in the late distal tubule and collecting ducts by
promoting insertion of aquaporin-2 channels into the apical
membrane. Water then moves from the tubular lumen into the
hyperosmotic medullary interstitium and ultimately into the
1
,circulation. This concentrates urine and decreases free-water
excretion.
Question 2
A researcher studies a cell whose membrane is permeable to potassium
but essentially impermeable to intracellular proteins and other large
anions. The intracellular potassium concentration is substantially higher
than the extracellular concentration. Which force primarily determines
the resting membrane potential of this cell?
A. Calcium equilibrium potential
B. Sodium equilibrium potential
C. Potassium electrochemical gradient
D. Chloride pump activity
E. ATP concentration alone
Answer: C. Potassium electrochemical gradient
Rationale: At rest, many excitable cells have substantially greater
permeability to K⁺ than to Na⁺. Potassium tends to diffuse out of the
cell down its concentration gradient, leaving behind negatively
charged intracellular proteins and generating an electrical gradient
opposing further K⁺ efflux. The resting membrane potential therefore
approaches the K⁺ equilibrium potential.
Question 3
A patient develops severe diarrhea resulting in loss of bicarbonate-rich
intestinal fluid. His arterial blood gas shows a pH of 7.28, PCO₂ of 30
mm Hg, and HCO₃⁻ of 14 mEq/L. Which physiologic response is most
appropriate for the observed acid-base disturbance?
2
,A. Renal bicarbonate excretion
B. Decreased alveolar ventilation
C. Increased alveolar ventilation
D. Decreased renal ammonium excretion
E. Decreased hydrogen ion secretion by the distal nephron
Answer: C. Increased alveolar ventilation
Rationale: The patient has primary metabolic acidosis, evidenced by
reduced bicarbonate and reduced pH. Respiratory compensation
occurs through increased ventilation, which lowers arterial PCO₂ and
thereby decreases carbonic acid concentration. Renal compensation
also occurs over time through increased H⁺ secretion, bicarbonate
reclamation, and ammonium generation.
Question 4
A 35-year-old woman develops acute blood loss after trauma. Her mean
arterial pressure falls significantly. Which immediate cardiovascular
response is most likely mediated by the arterial baroreceptor reflex?
A. Increased parasympathetic activity to the sinoatrial node
B. Decreased sympathetic activity to resistance vessels
C. Increased vagal activity and decreased heart rate
D. Increased sympathetic activity and peripheral vasoconstriction
E. Decreased myocardial contractility
Answer: D. Increased sympathetic activity and peripheral
vasoconstriction
Rationale: Acute hemorrhage decreases arterial pressure and
therefore decreases stretch of carotid sinus and aortic arch
baroreceptors. Reduced baroreceptor firing increases sympathetic and
decreases parasympathetic outflow. The result is tachycardia,
3
, increased myocardial contractility, venoconstriction, and arteriolar
vasoconstriction, which help restore arterial pressure.
Question 5
A researcher measures oxygen transport in a healthy adult.
Approximately 98% of oxygen in arterial blood is carried in association
with hemoglobin. Which alteration would shift the oxyhemoglobin
dissociation curve to the right?
A. Decreased temperature
B. Decreased 2,3-BPG concentration
C. Increased blood pH
D. Increased PCO₂
E. Fetal hemoglobin expression
Answer: D. Increased PCO₂
Rationale: Increased PCO₂ shifts the oxyhemoglobin dissociation
curve to the right through the Bohr effect. Increased temperature,
increased H⁺ concentration, and increased 2,3-BPG have similar
effects. A rightward shift decreases hemoglobin's affinity for oxygen
and facilitates oxygen unloading in metabolically active tissues.
Question 6
A patient has a mutation that prevents insertion of aquaporin-2 water
channels into the apical membrane of collecting duct principal cells
despite normal production of antidiuretic hormone. Which abnormality
is most likely?
A. Concentrated urine with low volume
B. Dilute urine with increased volume
C. Decreased plasma osmolality caused by water retention
4
PRACTICE EXAM WITH ACTUAL
QUESTIONS AND VERIFIED ANSWERS,
PLUS EXPLAINED RATIONALES/EXPERT
VERIFIED FOR GUARANTEED 100% PASS
2026/LATEST UPDATE/INSTANT
DOWNLOAD PDF
Question 1
A 24-year-old healthy man undergoes an experimental study of renal
physiology. His plasma sodium concentration is 140 mEq/L, and his
extracellular fluid volume is normal. Researchers administer a substance
that selectively increases the permeability of the collecting duct to water
without directly changing sodium transport. Which change would most
directly occur as a result?
A. Increased intracellular sodium concentration in collecting duct
principal cells
B. Increased water reabsorption from the tubular lumen
C. Decreased medullary interstitial osmolality
D. Increased renal plasma flow
E. Decreased glomerular filtration rate
Answer: B. Increased water reabsorption from the tubular lumen
Rationale: Antidiuretic hormone increases water permeability of
principal cells in the late distal tubule and collecting ducts by
promoting insertion of aquaporin-2 channels into the apical
membrane. Water then moves from the tubular lumen into the
hyperosmotic medullary interstitium and ultimately into the
1
,circulation. This concentrates urine and decreases free-water
excretion.
Question 2
A researcher studies a cell whose membrane is permeable to potassium
but essentially impermeable to intracellular proteins and other large
anions. The intracellular potassium concentration is substantially higher
than the extracellular concentration. Which force primarily determines
the resting membrane potential of this cell?
A. Calcium equilibrium potential
B. Sodium equilibrium potential
C. Potassium electrochemical gradient
D. Chloride pump activity
E. ATP concentration alone
Answer: C. Potassium electrochemical gradient
Rationale: At rest, many excitable cells have substantially greater
permeability to K⁺ than to Na⁺. Potassium tends to diffuse out of the
cell down its concentration gradient, leaving behind negatively
charged intracellular proteins and generating an electrical gradient
opposing further K⁺ efflux. The resting membrane potential therefore
approaches the K⁺ equilibrium potential.
Question 3
A patient develops severe diarrhea resulting in loss of bicarbonate-rich
intestinal fluid. His arterial blood gas shows a pH of 7.28, PCO₂ of 30
mm Hg, and HCO₃⁻ of 14 mEq/L. Which physiologic response is most
appropriate for the observed acid-base disturbance?
2
,A. Renal bicarbonate excretion
B. Decreased alveolar ventilation
C. Increased alveolar ventilation
D. Decreased renal ammonium excretion
E. Decreased hydrogen ion secretion by the distal nephron
Answer: C. Increased alveolar ventilation
Rationale: The patient has primary metabolic acidosis, evidenced by
reduced bicarbonate and reduced pH. Respiratory compensation
occurs through increased ventilation, which lowers arterial PCO₂ and
thereby decreases carbonic acid concentration. Renal compensation
also occurs over time through increased H⁺ secretion, bicarbonate
reclamation, and ammonium generation.
Question 4
A 35-year-old woman develops acute blood loss after trauma. Her mean
arterial pressure falls significantly. Which immediate cardiovascular
response is most likely mediated by the arterial baroreceptor reflex?
A. Increased parasympathetic activity to the sinoatrial node
B. Decreased sympathetic activity to resistance vessels
C. Increased vagal activity and decreased heart rate
D. Increased sympathetic activity and peripheral vasoconstriction
E. Decreased myocardial contractility
Answer: D. Increased sympathetic activity and peripheral
vasoconstriction
Rationale: Acute hemorrhage decreases arterial pressure and
therefore decreases stretch of carotid sinus and aortic arch
baroreceptors. Reduced baroreceptor firing increases sympathetic and
decreases parasympathetic outflow. The result is tachycardia,
3
, increased myocardial contractility, venoconstriction, and arteriolar
vasoconstriction, which help restore arterial pressure.
Question 5
A researcher measures oxygen transport in a healthy adult.
Approximately 98% of oxygen in arterial blood is carried in association
with hemoglobin. Which alteration would shift the oxyhemoglobin
dissociation curve to the right?
A. Decreased temperature
B. Decreased 2,3-BPG concentration
C. Increased blood pH
D. Increased PCO₂
E. Fetal hemoglobin expression
Answer: D. Increased PCO₂
Rationale: Increased PCO₂ shifts the oxyhemoglobin dissociation
curve to the right through the Bohr effect. Increased temperature,
increased H⁺ concentration, and increased 2,3-BPG have similar
effects. A rightward shift decreases hemoglobin's affinity for oxygen
and facilitates oxygen unloading in metabolically active tissues.
Question 6
A patient has a mutation that prevents insertion of aquaporin-2 water
channels into the apical membrane of collecting duct principal cells
despite normal production of antidiuretic hormone. Which abnormality
is most likely?
A. Concentrated urine with low volume
B. Dilute urine with increased volume
C. Decreased plasma osmolality caused by water retention
4
