USMLE Physiology 2

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?

Accepted Answer

Phase 2 (plateau phase)

Answer

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?

Accepted Answer

Hypokalemia and hypertension

Answer

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?

Accepted Answer

Decreased FEV1/FVC ratio (<0.70)

Answer

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?

Accepted Answer

Decreased renal perfusion pressure

Answer

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?

Accepted Answer

Increased V/Q ratio (dead space physiology)

Answer

PE blocks perfusion to a ventilated lung segment, increasing V/Q ratio toward infinity (dead space effect), wasting ventilation without gas exchange.

USMLE Practice Test

USMLE Practice Test

USMLE Physiology 2