Physiology
Core framework
Physiology questions test mechanisms and the direction of change. For any perturbation, reason through the sensor, the integrating center, and the effector, then predict the direction of the compensatory response. Core areas are membrane potentials and action potentials, cardiac cycle and hemodynamics, respiratory mechanics and gas exchange, renal handling of sodium, water, and acid, endocrine feedback loops, and thermoregulation.
Concepts you must own
The determinants of cardiac output and blood pressure. Starling forces across capillaries. Oxygen–hemoglobin dissociation curve shifts. Renal clearance and the concept of transport maximum. Hormonal feedback (thyroid, adrenal, calcium, glucose). The difference between a regulated variable and its effector.
Traps
- Direction questions: identify the primary disturbance first, then the compensation; they act in opposite directions.
- Clearance: clearance exceeds filtration only when secretion occurs.
- Curve shifts: right shift means reduced affinity and easier unloading; do not confuse it with reduced carrying capacity.
- Units and normal ranges are often the only discriminator between two plausible options.
Worked rule of thumb
For capillary fluid movement, apply Starling forces: filtration is driven by hydrostatic pressure and opposed by oncotic pressure. If plasma oncotic pressure falls, filtration increases and edema follows. If venous hydrostatic pressure rises, the same result occurs. Use this to predict edema in hypoalbuminemia and in heart failure without memorizing each case.