Physiology

The pressure–volume (PV) loop maps one heartbeat as LV pressure vs. volume, traced counterclockwise through four phases. Mastering its corners, valve-opening points, and how preload, afterload, and contractility reshape it unlocks the cardiac cycle, heart sounds, and JVP waveforms tested on Step 1.

A Step 1 tour of pulmonary gas exchange — Fick's law, diffusion vs perfusion limitation, and the A–a gradient — anchored to the sigmoidal oxygen–hemoglobin dissociation curve, its right/left shifts, and the classic dyshemoglobinemias (CO, methemoglobin, HbF).

A Step 1-focused walk through nephron segment transport (transporters, % Na⁺ reabsorbed, diuretic sites) and the clearance framework (GFR, RPF, FF, TF/P, glucose titration, free-water clearance), tied to the hormonal loops and channelopathies the boards test. Emphasis on the exact numbers, curves, and mechanism-to-disease correlations.

A Step 1-focused tour of the hypothalamic-pituitary axes, built around the three-tier feedback logic that localizes disease (primary/secondary/tertiary), the second-messenger buckets every hormone falls into, and the classic clinical breaks — adrenal insufficiency and prolactinoma. Emphasizes the rules the boards actually test: pulsatile GnRH, diurnal cortisol, POMC-driven hyperpigmentation, and mid-cycle estrogen positive feedback.

A Step 1-focused tour of GI secretion and motility built around two hubs — the parietal cell (three secretagogues, H⁺/K⁺-ATPase, alkaline tide) and the interstitial cells of Cajal (slow waves, MMC) — with the GI-hormone table, pancreatic/salivary flow-rate curves, feedback loops, and mechanism-driven vignettes (Zollinger-Ellison, achalasia, pernicious anemia).

A Step 1-focused walk through the neuronal action potential (resting potential, channel gating, refractory periods, conduction) and chemical synaptic transmission at the NMJ, anchored to the numbers, curves, and feedback the boards test — plus the classic disease correlations (MG vs LEMS, botulinum/tetanus, hyperkalemia, demyelination, local anesthetics).

A Step 1–focused muscle physiology lesson contrasting skeletal, cardiac, and smooth muscle across the cross-bridge cycle, the three EC-coupling wiring diagrams, and the length–tension/force–velocity curves, anchored by high-yield clinical correlations (malignant hyperthermia, digoxin inotropy, Duchenne). Emphasizes the tested numbers, transporters, and second-messenger contrasts.

A Step 1 walkthrough of body fluid compartments (60-40-20 rule, dilution tracers, effective osmoles) and the two independent control systems that defend osmolality (ADH/thirst) versus effective circulating volume (RAAS/ANP), anchored by Darrow-Yannet fluid shifts and the classic sodium/potassium clinical correlations (SIADH, diabetes insipidus, hyperkalemia).