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Physiology Flashcards

7 cards from real NBME 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. An arterial blood gas shows pH 7.28, PaCO2 28 mmHg, HCO3- 13 mEq/L. What is the primary disorder?

    Answer: Metabolic acidosis with respiratory compensation

    Low pH with low HCO3- indicates metabolic acidosis; the low PaCO2 reflects appropriate respiratory (Kussmaul) compensation.

  2. Where is the majority (~80–85%) of filtered bicarbonate reabsorbed?

    Answer: Proximal convoluted tubule

    The proximal tubule reabsorbs ~80–85% of filtered HCO3- via carbonic anhydrase-dependent H+ secretion and HCO3-/Na+ cotransport.

  3. Aldosterone's primary effect on the collecting duct principal cells is:

    Answer: Increasing Na+ reabsorption and K+ secretion

    Aldosterone upregulates apical ENaC and basolateral Na+/K+-ATPase, promoting sodium retention and potassium excretion.

  4. Inulin is the gold standard for measuring GFR because it is:

    Answer: Freely filtered, not reabsorbed, and not secreted

    Inulin is freely filtered at the glomerulus and undergoes no tubular reabsorption or secretion, so its clearance equals GFR exactly.

  5. A patient with chronic vomiting develops hypokalemia and metabolic alkalosis. The alkalosis is primarily caused by:

    Answer: Loss of HCl from gastric secretions

    Vomiting removes HCl, depleting H+ and raising serum HCO3-, resulting in metabolic alkalosis with contraction of ECF volume.

  6. Furosemide produces diuresis primarily by inhibiting which transporter?

    Answer: Na-K-2Cl cotransporter in the thick ascending limb

    Furosemide blocks the NKCC2 cotransporter in the thick ascending limb, disrupting the countercurrent multiplier and producing copious dilute urine.

  7. Antidiuretic hormone (ADH/vasopressin) increases water reabsorption by:

    Answer: Inserting aquaporin-2 channels in the collecting duct apical membrane

    ADH stimulates V2 receptors on collecting duct principal cells, triggering cAMP-mediated insertion of aquaporin-2 channels into the apical membrane.