Applying core physiologic mechanisms to bedside clinical scenarios and lab interpretation as tested on USMLE Step 2 CK.
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- What does the Frank-Starling law state about the heart?
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Increased venous return (preload) increases stroke volume, up to a physiologic limit.- What is cardiac preload?
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The ventricular wall stress (stretch) at the end of diastole, determined by venous return.- What is cardiac afterload?
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The resistance the ventricle must overcome to eject blood, largely set by systemic vascular resistance.- Cardiac output is calculated as CO = ____.
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heart rate x stroke volume- What happens to ejection fraction in heart failure with reduced EF (systolic heart failure)?
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It is decreased (below 40 percent), reflecting impaired contractility.- How does the baroreceptor reflex respond to acute hemorrhage?
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Decreased arterial pressure lowers baroreceptor firing, increasing sympathetic outflow and raising heart rate and vascular tone.- What is the Cushing triad seen with rising intracranial pressure?
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Hypertension, bradycardia, and irregular respirations.- Winter's formula predicts the expected respiratory compensation in metabolic acidosis: expected PCO2 = ____.
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1.5 x HCO3 + 8 (plus or minus 2)- The serum anion gap is calculated as ____.
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Na+ minus (Cl- + HCO3-)- Name a common cause of high anion gap metabolic acidosis related to tissue hypoperfusion.
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Lactic acidosis.- In a hypoxemia workup, what does a normal A-a gradient suggest as the underlying cause?
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Hypoventilation (or high altitude) rather than V/Q mismatch, shunt, or a diffusion defect.- What stimulates renin release from juxtaglomerular cells?
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Decreased afferent arteriole pressure, decreased NaCl delivery to the macula densa, or increased sympathetic stimulation.- What are the two main actions of angiotensin II?
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Systemic vasoconstriction and stimulation of aldosterone release from the adrenal cortex.- What does aldosterone do at the renal collecting duct?
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Increases sodium reabsorption and potassium secretion.- By what mechanism does ADH (vasopressin) increase water reabsorption?
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It inserts aquaporin-2 water channels into the collecting duct principal cells.
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