PCAT Physiology 4 — Questions and Answers
Question 1: A patient with SIADH (syndrome of inappropriate ADH secretion) would present with which lab finding?
- Hypernatremia with dilute urine
- Hyponatremia with concentrated urine (Correct answer)
- Hyperkalemia with alkalosis
- Hypernatremia with concentrated urine
Correct answer: Hyponatremia with concentrated urine
Excess ADH causes water retention, diluting serum Na⁺ (hyponatremia) while the urine remains inappropriately concentrated due to continued water reabsorption.
Question 2: Which phase of the cardiac cycle is associated with the first heart sound (S1)?
- Opening of the aortic valve
- Closure of the mitral and tricuspid valves (Correct answer)
- Rapid ventricular filling
- Closure of the aortic and pulmonic valves
Correct answer: Closure of the mitral and tricuspid valves
S1 is produced by the closure of the AV valves (mitral and tricuspid) at the onset of systole when ventricular pressure exceeds atrial pressure.
Question 3: During inspiration, intrathoracic pressure decreases. This primarily causes:
- Decreased venous return to the right heart
- Increased venous return and right heart filling (Correct answer)
- Pulmonary vasoconstriction
- Decreased tidal volume
Correct answer: Increased venous return and right heart filling
Negative intrathoracic pressure during inspiration expands the great veins and right atrium, drawing blood into the thoracic cavity and increasing venous return.
Question 4: The respiratory system's primary defense against acidosis from CO₂ retention is:
- Decreased bicarbonate production by kidneys
- Increased respiratory rate to blow off CO₂ (Correct answer)
- Reduced hemoglobin buffering capacity
- Activation of the renin-angiotensin system
Correct answer: Increased respiratory rate to blow off CO₂
Chemoreceptors sense rising PCO₂/falling pH and drive increased ventilation, expiring more CO₂ and rapidly correcting respiratory acidosis.
Question 5: Intestinal glucose absorption against its concentration gradient depends on which cotransport mechanism?
- GLUT2 facilitated diffusion
- Na⁺/glucose cotransporter (SGLT1) powered by Na⁺ gradient (Correct answer)
- ATP-driven glucose pump directly
- Cl⁻/glucose antiporter
Correct answer: Na⁺/glucose cotransporter (SGLT1) powered by Na⁺ gradient
SGLT1 couples glucose uptake to Na⁺ entry down its electrochemical gradient, which is maintained by basolateral Na⁺/K⁺-ATPase—secondary active transport.
Question 6: Which autonomic change occurs during the diving reflex in humans?
- Tachycardia and vasodilation
- Bradycardia and peripheral vasoconstriction (Correct answer)
- Increased respiratory rate
- Decreased systemic blood pressure
Correct answer: Bradycardia and peripheral vasoconstriction
Cold water facial immersion triggers vagal bradycardia and sympathetic peripheral vasoconstriction, shunting blood to vital organs (heart and brain).
Question 7: Secretin, released by S cells in the duodenum, primarily stimulates:
- Gastric acid secretion by parietal cells
- Pancreatic bicarbonate secretion to neutralize acid (Correct answer)
- Gallbladder contraction for bile release
- Gastric emptying acceleration
Correct answer: Pancreatic bicarbonate secretion to neutralize acid
Acidic chyme in the duodenum triggers secretin release, which acts on pancreatic ductal cells to secrete HCO₃⁻-rich fluid that neutralizes gastric acid.
PCAT Physiology 4
A patient with SIADH (syndrome of inappropriate ADH secretion) would present with which lab finding?