PHYS 261 MIDTERM EXAM / ACTUAL PHYS
HUMAN PHYSIOLOGY MIDTERM EXAM WEST
COAST UNIVERSITY (WCU) 2026/2027 HIGH YIELD
PRACTICE QUESTIONS AND STUDY GUIDE
ACCURATE EXAM COMPLETE REAL QUESTIONS
AND CORRECT VERIFIED ANSWERS WITH
DETAILED RATIONALES (RE - Complete 49
Verified Q&A with Answers & Rationales for Exam
Prep
Q1
In a skeletal muscle fiber, which molecular event directly precedes the release of Ca² from the
sarcoplasmic reticulum?
A. ATP binding to the myosin head
B. Depolarization of the T-tubule activating the dihydropyridine receptor
C. Binding of acetylcholine to nicotinic receptors
D. Phosphorylation of the ryanodine receptor by PKA
Answer: B
Rationale: T-tubule depolarization activates the voltage-sensing dihydropyridine receptor (DHPR), which
mechanically couples to and opens the ryanodine receptor (RyR1) to release Ca². ACh binding initiates
the action potential but does not directly gate SR Ca² release. ATP binding to myosin is part of the
cross-bridge cycle, not EC coupling. PKA phosphorylation modulates RyR but is not the primary trigger.
,Q2
A patient has a mutation in the -subunit of the epithelial sodium channel (ENaC) in the collecting duct,
causing constitutive activation. Which set of changes is most likely?
A. Hyponatremia, hyperkalemia, metabolic acidosis
B. Hypernatremia, hypokalemia, metabolic alkalosis
C. Hypernatremia, hyperkalemia, metabolic acidosis
D. Hyponatremia, hypokalemia, metabolic alkalosis
Answer: B
Rationale: Constitutive ENaC activity increases Na z reabsorption, leading to hypernatremia and volume
expansion; increased Na reabsorption creates a lumen-negative potential that drives K secretion, causing
hypokalemia; and enhanced H secretion contributes to metabolic alkalosis. The other options incorrectly
pair these electrolyte and acid-base disturbances.
Q3
Which of the following best explains why cardiac muscle exhibits a longer refractory period than skeletal
muscle?
A. Cardiac muscle has a more negative resting membrane potential.
B. Cardiac muscle action potentials include a plateau phase due to slow Ca² influx.
C. Cardiac muscle relies exclusively on anaerobic metabolism.
D. Cardiac muscle lacks T-tubules, delaying repolarization.
Answer: B
Rationale: The plateau phase in cardiac action potentials, caused by slow L-type Ca² z channel influx,
prolongs depolarization and extends the refractory period, preventing tetany. Skeletal muscle lacks this
plateau. The other options are factually incorrect regarding cardiac muscle properties.
Q4
In the pulmonary circulation, hypoxic vasoconstriction occurs. Which mechanism best explains this
response?
A. Inhibition of voltage-gated K channels in pulmonary artery smooth muscle cells
B. Activation of ATP-sensitive K channels
C. Increased production of nitric oxide by endothelial cells
D. Upregulation of prostacyclin synthesis
Answer: A
Rationale: Hypoxia inhibits voltage-gated K z channels in pulmonary artery smooth muscle, causing
membrane depolarization, Ca² influx, and vasoconstriction. This diverts blood from poorly ventilated
areas. The other options would promote vasodilation or are not primary mechanisms.
, Q5
A drug inhibits carbonic anhydrase in the proximal tubule. Which change in urine composition is expected?
A. Increased HCO reabsorption and decreased Na excretion
B. Decreased HCO reabsorption and increased Na excretion
C. Increased H secretion and increased K reabsorption
D. Decreased water reabsorption and increased glucose excretion
Answer: B
Rationale: Carbonic anhydrase inhibition reduces HCO ƒ { reabsorption because H z secretion is impaired,
leading to increased urinary HCO and Na excretion. The other options describe effects opposite to
carbonic anhydrase inhibition.
Q6
Which statement accurately describes the role of the sarcoplasmic reticulum in smooth muscle compared
to skeletal muscle?
A. Smooth muscle SR is more extensive and stores more Ca².
B. Smooth muscle relies solely on extracellular Ca² for contraction.
C. Smooth muscle SR is less developed, and Ca² also enters from the extracellular fluid.
D. Smooth muscle SR lacks ryanodine receptors entirely.
Answer: C
Rationale: Smooth muscle has a less developed SR and depends on both SR Ca² z release and
extracellular Ca² influx via voltage- and ligand-gated channels. Skeletal muscle has a more extensive SR.
The other options are incorrect regarding smooth muscle Ca² handling.
Q7
A patient with severe anemia has a normal arterial PO but reduced oxygen content. Which compensatory
mechanism is most likely to maintain tissue oxygenation?
A. Increased 2,3-BPG levels shifting the oxyhemoglobin dissociation curve to the right
B. Decreased heart rate to prolong capillary transit time
C. Increased plasma protein binding of oxygen
D. Reduced erythropoietin secretion
Answer: A
Rationale: In anemia, increased 2,3-BPG shifts the curve right, enhancing O ‚ unloading to tissues.
Reduced erythropoietin would worsen anemia. The other options do not improve tissue oxygenation.
HUMAN PHYSIOLOGY MIDTERM EXAM WEST
COAST UNIVERSITY (WCU) 2026/2027 HIGH YIELD
PRACTICE QUESTIONS AND STUDY GUIDE
ACCURATE EXAM COMPLETE REAL QUESTIONS
AND CORRECT VERIFIED ANSWERS WITH
DETAILED RATIONALES (RE - Complete 49
Verified Q&A with Answers & Rationales for Exam
Prep
Q1
In a skeletal muscle fiber, which molecular event directly precedes the release of Ca² from the
sarcoplasmic reticulum?
A. ATP binding to the myosin head
B. Depolarization of the T-tubule activating the dihydropyridine receptor
C. Binding of acetylcholine to nicotinic receptors
D. Phosphorylation of the ryanodine receptor by PKA
Answer: B
Rationale: T-tubule depolarization activates the voltage-sensing dihydropyridine receptor (DHPR), which
mechanically couples to and opens the ryanodine receptor (RyR1) to release Ca². ACh binding initiates
the action potential but does not directly gate SR Ca² release. ATP binding to myosin is part of the
cross-bridge cycle, not EC coupling. PKA phosphorylation modulates RyR but is not the primary trigger.
,Q2
A patient has a mutation in the -subunit of the epithelial sodium channel (ENaC) in the collecting duct,
causing constitutive activation. Which set of changes is most likely?
A. Hyponatremia, hyperkalemia, metabolic acidosis
B. Hypernatremia, hypokalemia, metabolic alkalosis
C. Hypernatremia, hyperkalemia, metabolic acidosis
D. Hyponatremia, hypokalemia, metabolic alkalosis
Answer: B
Rationale: Constitutive ENaC activity increases Na z reabsorption, leading to hypernatremia and volume
expansion; increased Na reabsorption creates a lumen-negative potential that drives K secretion, causing
hypokalemia; and enhanced H secretion contributes to metabolic alkalosis. The other options incorrectly
pair these electrolyte and acid-base disturbances.
Q3
Which of the following best explains why cardiac muscle exhibits a longer refractory period than skeletal
muscle?
A. Cardiac muscle has a more negative resting membrane potential.
B. Cardiac muscle action potentials include a plateau phase due to slow Ca² influx.
C. Cardiac muscle relies exclusively on anaerobic metabolism.
D. Cardiac muscle lacks T-tubules, delaying repolarization.
Answer: B
Rationale: The plateau phase in cardiac action potentials, caused by slow L-type Ca² z channel influx,
prolongs depolarization and extends the refractory period, preventing tetany. Skeletal muscle lacks this
plateau. The other options are factually incorrect regarding cardiac muscle properties.
Q4
In the pulmonary circulation, hypoxic vasoconstriction occurs. Which mechanism best explains this
response?
A. Inhibition of voltage-gated K channels in pulmonary artery smooth muscle cells
B. Activation of ATP-sensitive K channels
C. Increased production of nitric oxide by endothelial cells
D. Upregulation of prostacyclin synthesis
Answer: A
Rationale: Hypoxia inhibits voltage-gated K z channels in pulmonary artery smooth muscle, causing
membrane depolarization, Ca² influx, and vasoconstriction. This diverts blood from poorly ventilated
areas. The other options would promote vasodilation or are not primary mechanisms.
, Q5
A drug inhibits carbonic anhydrase in the proximal tubule. Which change in urine composition is expected?
A. Increased HCO reabsorption and decreased Na excretion
B. Decreased HCO reabsorption and increased Na excretion
C. Increased H secretion and increased K reabsorption
D. Decreased water reabsorption and increased glucose excretion
Answer: B
Rationale: Carbonic anhydrase inhibition reduces HCO ƒ { reabsorption because H z secretion is impaired,
leading to increased urinary HCO and Na excretion. The other options describe effects opposite to
carbonic anhydrase inhibition.
Q6
Which statement accurately describes the role of the sarcoplasmic reticulum in smooth muscle compared
to skeletal muscle?
A. Smooth muscle SR is more extensive and stores more Ca².
B. Smooth muscle relies solely on extracellular Ca² for contraction.
C. Smooth muscle SR is less developed, and Ca² also enters from the extracellular fluid.
D. Smooth muscle SR lacks ryanodine receptors entirely.
Answer: C
Rationale: Smooth muscle has a less developed SR and depends on both SR Ca² z release and
extracellular Ca² influx via voltage- and ligand-gated channels. Skeletal muscle has a more extensive SR.
The other options are incorrect regarding smooth muscle Ca² handling.
Q7
A patient with severe anemia has a normal arterial PO but reduced oxygen content. Which compensatory
mechanism is most likely to maintain tissue oxygenation?
A. Increased 2,3-BPG levels shifting the oxyhemoglobin dissociation curve to the right
B. Decreased heart rate to prolong capillary transit time
C. Increased plasma protein binding of oxygen
D. Reduced erythropoietin secretion
Answer: A
Rationale: In anemia, increased 2,3-BPG shifts the curve right, enhancing O ‚ unloading to tissues.
Reduced erythropoietin would worsen anemia. The other options do not improve tissue oxygenation.
