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Physiology Flashcards

7 cards from real PCAT practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

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

    Answer: Loop of Henle

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

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

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

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

  3. Surfactant produced by type II pneumocytes primarily functions to:

    Answer: Decrease alveolar surface tension to prevent collapse

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

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

    Answer: β₁-adrenergic receptors in the SA node

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

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

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

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

  6. Glomerular filtration rate (GFR) is best clinically estimated using:

    Answer: Plasma creatinine concentration and equations like CKD-EPI

    Creatinine is freely filtered and minimally secreted, so serum creatinine-based equations (CKD-EPI, MDRD) provide the standard GFR estimate in clinical practice.

  7. Which neurotransmitter is released at the neuromuscular junction to initiate skeletal muscle contraction?

    Answer: Acetylcholine

    Acetylcholine released from motor neurons binds nicotinic receptors on the motor end plate, triggering an end-plate potential that leads to muscle contraction.