USMLE Physiology 2 — Questions and Answers
Question 1: Which phase of the cardiac action potential in ventricular cardiomyocytes is responsible for the prolonged plateau and is mediated by L-type calcium channels?
- Phase 2 (plateau phase) (Correct answer)
- Phase 0 (rapid depolarization)
- Phase 3 (rapid repolarization)
- Phase 4 (resting membrane potential)
Correct answer: Phase 2 (plateau phase)
Phase 2 of the ventricular action potential is the plateau phase maintained by calcium influx through L-type (long-lasting) calcium channels, balanced by potassium efflux.
Question 2: A patient with primary hyperaldosteronism (Conn syndrome) will have which electrolyte abnormality?
- Hypokalemia and hypertension (Correct answer)
- Hyperkalemia and hypertension
- Hyponatremia and hypotension
- Hypernatremia and hypotension
Correct answer: Hypokalemia and hypertension
Excess aldosterone promotes sodium retention and potassium excretion in the collecting duct, causing hypertension (volume expansion) and hypokalemia.
Question 3: Which pulmonary function test finding is characteristic of obstructive lung disease?
- Decreased FEV1/FVC ratio (<0.70) (Correct answer)
- Decreased FVC with normal FEV1/FVC ratio
- Increased TLC with decreased FVC
- Decreased DLCO only
Correct answer: Decreased FEV1/FVC ratio (<0.70)
Obstructive diseases (asthma, COPD, emphysema) show decreased FEV1/FVC ratio (<0.70) because airflow obstruction disproportionately reduces FEV1 more than FVC.
Question 4: The juxtaglomerular apparatus (JGA) releases renin in response to which stimulus?
- Decreased renal perfusion pressure (Correct answer)
- Increased sodium delivery to the macula densa
- Increased blood pressure
- Increased angiotensin II
Correct answer: Decreased renal perfusion pressure
JGA granular cells release renin in response to decreased renal perfusion pressure (baroreceptor mechanism), decreased NaCl at the macula densa, and sympathetic stimulation (beta-1 receptors).
Question 5: A patient has a positive D-dimer test and imaging confirms pulmonary embolism. Which ventilation-perfusion change occurs in the affected lung segment?
- Increased V/Q ratio (dead space physiology) (Correct answer)
- Decreased V/Q ratio (shunt physiology)
- Normal V/Q ratio
- Decreased ventilation with normal perfusion
Correct answer: Increased V/Q ratio (dead space physiology)
PE blocks perfusion to a ventilated lung segment, increasing V/Q ratio toward infinity (dead space effect), wasting ventilation without gas exchange.
Question 6: Insulin promotes glucose uptake in muscle and adipose tissue by stimulating translocation of which glucose transporter?
- GLUT4 (Correct answer)
- GLUT1
- GLUT2
- GLUT3
Correct answer: GLUT4
Insulin stimulates translocation of GLUT4-containing vesicles to the plasma membrane in muscle and adipose tissue, increasing glucose uptake via PI3K-Akt signaling.
USMLE Physiology 2
Which phase of the cardiac action potential in ventricular cardiomyocytes is responsible for the prolonged plateau and is mediated by L-type calcium channels?