Test Bank for Costanzo Physiology 8th edition|
2026 Update |A+ Graded | Answers with
Rationale
,Chapter 1: Cellular Physiology
1. A 65-year-old man with chronic kidney disease presents with fatigue and confusion. Laboratory
tests reveal hyperkalemia. Which change in membrane potential is most likely occurring in his
neurons?
A. Hyperpolarization due to increased K⁺ efflux
B. Depolarization due to decreased K⁺ efflux
C. Depolarization due to increased Na⁺ influx
D. Hyperpolarization due to increased Cl⁻ influx
ANS: B
Rationale:
Elevated extracellular potassium reduces the concentration gradient for K⁺ efflux. This decreases
potassium movement out of the cell, making the resting membrane potential less negative, leading to
depolarization. This increases neuronal excitability and explains neurologic symptoms.
2. A researcher blocks Na⁺/K⁺-ATPase activity in cultured neurons. Which immediate cellular
change is expected?
A. Increased intracellular Na⁺ and decreased K⁺
B. Decreased intracellular Na⁺ and increased K⁺
C. Increased intracellular Ca²⁺
D. Increased chloride efflux
ANS: A
Rationale:
The Na⁺/K⁺ pump normally extrudes 3 Na⁺ and imports 2 K⁺. Inhibition leads to accumulation of Na⁺
inside the cell and loss of intracellular K⁺, disrupting resting membrane potential and cell volume
regulation.
3. A patient with ischemic stroke develops cerebral edema. Failure of which cellular mechanism
most directly contributes to neuronal swelling?
A. Voltage-gated Na⁺ channels
B. Ligand-gated K⁺ channels
C. Na⁺/K⁺-ATPase
D. Ca²⁺-ATPase
ANS: C
,Rationale:
Ischemia reduces ATP production. Loss of Na⁺/K⁺-ATPase function causes Na⁺ accumulation, followed by
water influx through osmosis, resulting in cytotoxic edema and neuronal swelling.
4. A toxin increases membrane permeability to sodium ions. What is the primary effect on resting
membrane potential?
A. Hyperpolarization
B. Depolarization
C. No change
D. Stabilization near equilibrium potential of potassium
ANS: B
Rationale:
Increased Na⁺ permeability allows sodium to enter the cell down its electrochemical gradient, shifting
membrane potential toward the Na⁺ equilibrium potential and causing depolarization.
5. A patient has a genetic defect in aquaporin channels. Which process is most impaired?
A. Active transport of ions
B. Facilitated diffusion of glucose
C. Osmotic water movement
D. Endocytosis
ANS: C
Rationale:
Aquaporins facilitate rapid passive water movement across membranes. Defects reduce osmotic water
permeability, impairing cell volume regulation.
6. A laboratory measures membrane potential after increasing extracellular chloride. What is the
expected effect in most neurons?
A. Depolarization
B. Hyperpolarization
C. No change
D. Action potential generation
ANS: B
Rationale:
Increased extracellular chloride enhances Cl⁻ influx, making the membrane more negative and
producing hyperpolarization.
, 7. A drug selectively blocks voltage-gated calcium channels. Which cellular process is most
affected?
A. Resting membrane potential
B. Neurotransmitter release
C. Glucose transport
D. Protein synthesis
ANS: B
Rationale:
Calcium influx through voltage-gated channels triggers synaptic vesicle fusion. Blocking these channels
inhibits neurotransmitter release.
8. A patient with severe diarrhea develops metabolic acidosis. How does this affect intracellular pH
regulation?
A. Increased Na⁺/H⁺ exchange
B. Decreased Na⁺/H⁺ exchange
C. Increased Cl⁻ secretion
D. Decreased bicarbonate reabsorption
ANS: A
Rationale:
Acidosis stimulates Na⁺/H⁺ exchangers, promoting hydrogen ion extrusion to restore intracellular pH.
9. Which characteristic best distinguishes facilitated diffusion from simple diffusion?
A. Requires ATP
B. Occurs against gradient
C. Shows saturation kinetics
D. Requires vesicles
ANS: C
Rationale:
Facilitated diffusion uses carrier proteins that become saturated at high substrate concentrations, unlike
simple diffusion.
10. A patient has hypocalcemia. Which effect on neuronal membranes is expected?
A. Decreased excitability
B. Increased excitability
2026 Update |A+ Graded | Answers with
Rationale
,Chapter 1: Cellular Physiology
1. A 65-year-old man with chronic kidney disease presents with fatigue and confusion. Laboratory
tests reveal hyperkalemia. Which change in membrane potential is most likely occurring in his
neurons?
A. Hyperpolarization due to increased K⁺ efflux
B. Depolarization due to decreased K⁺ efflux
C. Depolarization due to increased Na⁺ influx
D. Hyperpolarization due to increased Cl⁻ influx
ANS: B
Rationale:
Elevated extracellular potassium reduces the concentration gradient for K⁺ efflux. This decreases
potassium movement out of the cell, making the resting membrane potential less negative, leading to
depolarization. This increases neuronal excitability and explains neurologic symptoms.
2. A researcher blocks Na⁺/K⁺-ATPase activity in cultured neurons. Which immediate cellular
change is expected?
A. Increased intracellular Na⁺ and decreased K⁺
B. Decreased intracellular Na⁺ and increased K⁺
C. Increased intracellular Ca²⁺
D. Increased chloride efflux
ANS: A
Rationale:
The Na⁺/K⁺ pump normally extrudes 3 Na⁺ and imports 2 K⁺. Inhibition leads to accumulation of Na⁺
inside the cell and loss of intracellular K⁺, disrupting resting membrane potential and cell volume
regulation.
3. A patient with ischemic stroke develops cerebral edema. Failure of which cellular mechanism
most directly contributes to neuronal swelling?
A. Voltage-gated Na⁺ channels
B. Ligand-gated K⁺ channels
C. Na⁺/K⁺-ATPase
D. Ca²⁺-ATPase
ANS: C
,Rationale:
Ischemia reduces ATP production. Loss of Na⁺/K⁺-ATPase function causes Na⁺ accumulation, followed by
water influx through osmosis, resulting in cytotoxic edema and neuronal swelling.
4. A toxin increases membrane permeability to sodium ions. What is the primary effect on resting
membrane potential?
A. Hyperpolarization
B. Depolarization
C. No change
D. Stabilization near equilibrium potential of potassium
ANS: B
Rationale:
Increased Na⁺ permeability allows sodium to enter the cell down its electrochemical gradient, shifting
membrane potential toward the Na⁺ equilibrium potential and causing depolarization.
5. A patient has a genetic defect in aquaporin channels. Which process is most impaired?
A. Active transport of ions
B. Facilitated diffusion of glucose
C. Osmotic water movement
D. Endocytosis
ANS: C
Rationale:
Aquaporins facilitate rapid passive water movement across membranes. Defects reduce osmotic water
permeability, impairing cell volume regulation.
6. A laboratory measures membrane potential after increasing extracellular chloride. What is the
expected effect in most neurons?
A. Depolarization
B. Hyperpolarization
C. No change
D. Action potential generation
ANS: B
Rationale:
Increased extracellular chloride enhances Cl⁻ influx, making the membrane more negative and
producing hyperpolarization.
, 7. A drug selectively blocks voltage-gated calcium channels. Which cellular process is most
affected?
A. Resting membrane potential
B. Neurotransmitter release
C. Glucose transport
D. Protein synthesis
ANS: B
Rationale:
Calcium influx through voltage-gated channels triggers synaptic vesicle fusion. Blocking these channels
inhibits neurotransmitter release.
8. A patient with severe diarrhea develops metabolic acidosis. How does this affect intracellular pH
regulation?
A. Increased Na⁺/H⁺ exchange
B. Decreased Na⁺/H⁺ exchange
C. Increased Cl⁻ secretion
D. Decreased bicarbonate reabsorption
ANS: A
Rationale:
Acidosis stimulates Na⁺/H⁺ exchangers, promoting hydrogen ion extrusion to restore intracellular pH.
9. Which characteristic best distinguishes facilitated diffusion from simple diffusion?
A. Requires ATP
B. Occurs against gradient
C. Shows saturation kinetics
D. Requires vesicles
ANS: C
Rationale:
Facilitated diffusion uses carrier proteins that become saturated at high substrate concentrations, unlike
simple diffusion.
10. A patient has hypocalcemia. Which effect on neuronal membranes is expected?
A. Decreased excitability
B. Increased excitability
