Source / episode info

• **Episode:**596
• **Title:**DIP Ep 596: 2025 USMLE Step 1 Free 120 Discussion Part 11b (Q106-110, super helpful for Step 2 and 3!)
• **Published:**2025-04-25
• Source:Episode page

One-liner

This episode integrates high-yield concepts covering primary hemostasis defects (VWD, Bernard-Soulier, Glanzmann), the physiological adaptations and complications of chronic high altitude exposure, the pathophysiology and management of HUS, the mechanisms of acute tubular necrosis, and classic infectious disease presentations like mumps.

High-yield summary

• Primary Hemostasis Defects: The Ristocetin Cofactor Assay tests adhesion (VWD/Bernard-Soulier); Thrombin time assesses fibrinogen function; Aggregation testing assesses GP2b3a function. Glanzmann Thrombasthenia is a quantitative defect of {GP}_{2{b}3}.
• High Altitude Physiology: Chronic hypoxia leads to pulmonary vasoconstriction and subsequent pulmonary hypertension (PH). PH causes chronic pressure overload, leading to right ventricular hypertrophy and decreased diastolic compliance.
• HUS Triad: The classic triad is thrombocytopenia, microangiopathic hemolytic anemia (schistocytes), and acute kidney injury (AKI). The most common cause is E. coli O157:H7 toxin.
• ATN Mechanism: In AKI, the proximal tubule is the most metabolically active segment and is therefore the first to fail during hypoperfusion or nephrotoxin exposure.
• Mumps Parotitis: The classic presentation involves fever, malaise, and painful swelling of the parotid glands; this is a key USMLE association.

Learning objectives

• Differentiate between primary hemostasis defects affecting adhesion, aggregation, and clotting factors.
• Describe the physiological changes in the cardiovascular system resulting from chronic high altitude hypoxia.
• Recognize the clinical triad, etiology, and management pitfalls of Hemolytic Uremic Syndrome (HUS).
• Identify the most susceptible segment of the kidney during acute tubular necrosis (ATN) due to hypoperfusion or nephrotoxins.
• Correlate classic signs and symptoms with specific infectious agents (e.g., Mumps parotitis, E. coli O157:H7).

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