PCAT Physiology 3

Question 1

Which portion of the nephron is responsible for creating the medullary osmotic gradient via the countercurrent multiplier?

Accepted Answer

Loop of Henle

Answer

The descending limb is water-permeable and the ascending limb actively pumps NaCl, generating a hypertonic medullary interstitium via countercurrent multiplication.

Question 2

During the plateau phase (phase 2) of the cardiac ventricular action potential, which ion movement predominates?

Accepted Answer

Ca²⁺ influx through L-type channels balancing K⁺ efflux

Answer

Slow Ca²⁺ entry through L-type voltage-gated channels counteracts K⁺ outflow, maintaining the prolonged plateau that prevents tetanic contraction.

Question 3

Surfactant produced by type II pneumocytes primarily functions to:

Accepted Answer

Decrease alveolar surface tension to prevent collapse

Answer

Dipalmitoylphosphatidylcholine (DPPC) in surfactant reduces surface tension, keeping small alveoli from collapsing per Laplace's law.

Question 4

Which receptor type mediates the baroreceptor reflex increase in heart rate when blood pressure drops?

Accepted Answer

β₁-adrenergic receptors in the SA node

Answer

Sympathetic activation during hypotension releases norepinephrine that binds β₁ receptors on the SA node, increasing cAMP and heart rate.

Question 5

The oxygen-hemoglobin dissociation curve shifts to the RIGHT in which condition?

Accepted Answer

Elevated 2,3-bisphosphoglycerate (2,3-BPG)

Answer

Increased 2,3-BPG (produced in exercising muscle) stabilizes deoxyhemoglobin, reducing O₂ affinity and promoting O₂ delivery to tissues.

PCAT - Pharmacy College Admission Test Practice Test

PCAT - Pharmacy College Admission Test Practice Test

PCAT Physiology 3