PCAT Physiology 2 — Questions and Answers
Question 1: Which ion is primarily responsible for the depolarization phase of a cardiac action potential in ventricular myocytes?
- Potassium (K⁺)
- Sodium (Na⁺) (Correct answer)
- Calcium (Ca²⁺)
- Chloride (Cl⁻)
Correct answer: Sodium (Na⁺)
Rapid Na⁺ influx through voltage-gated Na⁺ channels causes the sharp depolarization (phase 0) of ventricular action potentials.
Question 2: The Frank-Starling mechanism states that cardiac output increases when:
- Heart rate decreases below 60 bpm
- Ventricular end-diastolic volume increases (Correct answer)
- Systemic vascular resistance rises sharply
- Sympathetic tone is completely withdrawn
Correct answer: Ventricular end-diastolic volume increases
Greater ventricular filling (preload) stretches sarcomeres, improving actin-myosin overlap and increasing stroke volume.
Question 3: During exercise, which mechanism most directly increases venous return to the heart?
- Decreased cardiac contractility
- Skeletal muscle pump action (Correct answer)
- Increased parasympathetic tone
- Pulmonary vasoconstriction
Correct answer: Skeletal muscle pump action
Rhythmic contraction of skeletal muscles compresses veins and, combined with venous valves, propels blood toward the heart.
Question 4: Aldosterone primarily acts on which nephron segment to regulate sodium reabsorption?
- Proximal convoluted tubule
- Thick ascending limb of Henle
- Cortical collecting duct (Correct answer)
- Bowman's capsule
Correct answer: Cortical collecting duct
Aldosterone binds mineralocorticoid receptors in principal cells of the cortical collecting duct, upregulating ENaC and Na⁺/K⁺-ATPase.
Question 5: Which lung volume CANNOT be measured by spirometry alone?
- Tidal volume
- Inspiratory reserve volume
- Expiratory reserve volume
- Residual volume (Correct answer)
Correct answer: Residual volume
Residual volume is the air remaining after maximal exhalation and requires body plethysmography or helium dilution because it cannot be exhaled into a spirometer.
Question 6: The primary stimulus for erythropoietin (EPO) release from the kidneys is:
- Elevated blood glucose
- Hypoxia detected by peritubular cells (Correct answer)
- Increased serum iron levels
- Rising mean arterial pressure
Correct answer: Hypoxia detected by peritubular cells
Low O₂ tension activates HIF-1α in peritubular interstitial cells, triggering EPO gene transcription to stimulate RBC production.
Question 7: A patient has a plasma osmolality of 310 mOsm/kg. Which hormone is most likely elevated?
- Aldosterone
- Atrial natriuretic peptide
- Antidiuretic hormone (ADH) (Correct answer)
- Parathyroid hormone
Correct answer: Antidiuretic hormone (ADH)
Hyperosmolality (>290 mOsm/kg) strongly stimulates hypothalamic osmoreceptors to trigger ADH release from the posterior pituitary.
PCAT Physiology 2
Which ion is primarily responsible for the depolarization phase of a cardiac action potential in ventricular myocytes?