Physiology
Core concepts
Physiology asks how cells, organs, and systems maintain homeostasis. Understand membrane transport, resting and action potentials, synaptic transmission, muscle contraction, and autonomic control. In cardiovascular physiology, know the cardiac cycle, pressure-volume relationships, cardiac output as heart rate times stroke volume, and Starling forces. In respiratory physiology, know lung volumes, compliance, ventilation-perfusion matching, and hemoglobin-oxygen dissociation. Renal physiology emphasizes filtration, reabsorption, secretion, countercurrent multiplication, and hormonal control. Endocrine questions test feedback loops, receptor types, and hormone actions. Gastrointestinal physiology includes secretion, motility, and absorption.
Traps
Do not confuse ADH and aldosterone: ADH increases water reabsorption; aldosterone increases sodium reabsorption and potassium secretion. Insulin lowers blood glucose; glucagon raises it. In Starling forces, net filtration favors capillary hydrostatic pressure and interstitial oncotic pressure, while plasma oncotic pressure opposes filtration. A rightward shift of the hemoglobin curve means decreased affinity and easier oxygen unloading, not increased oxygen loading.
Worked example and rule of thumb
A working muscle increases CO2, H+, and temperature. These shift the hemoglobin-oxygen curve right, reducing affinity so oxygen unloads to tissue. Rule: right shift equals release; left shift equals tighter binding. Common left-shift causes include alkalosis, hypothermia, and low 2,3-BPG.
Exam focus
Use cause-and-effect reasoning rather than memorizing isolated numbers. Identify the regulated variable and the feedback direction.