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