Anatomy, Physiology and Pathophysiology
What this domain tests
Anatomy, Physiology and Pathophysiology tests structure-function relationships, homeostasis, and the mechanisms that produce clinical signs.
Core rules
- Cells adapt by hypertrophy, hyperplasia, atrophy, metaplasia, dysplasia, and neoplasia. Injury becomes irreversible when the cell cannot restore ATP and membrane integrity.
- Fluid shifts follow Starling forces: hydrostatic pressure pushes fluid out; oncotic pressure holds it in. Low albumin causes edema; high hydrostatic pressure causes pulmonary edema.
- Acid-base compensation: respiratory disorders are compensated by the kidneys over hours to days; metabolic disorders are compensated by ventilation within minutes.
- Hypovolemia triggers baroreceptors, sympathetic activation, renin-angiotensin-aldosterone, and ADH release, producing tachycardia, vasoconstriction, sodium and water retention, and low urine sodium.
- Inflammation has five cardinal signs: redness, heat, swelling, pain, and loss of function, driven by vasodilation and increased capillary permeability.
Worked example
A patient with prolonged vomiting has pH 7.50, PaCO2 46, and HCO3 34. Explain the findings. Reasoning: pH is alkalemic; HCO3 is high, so the primary problem is metabolic alkalosis from loss of gastric acid. PaCO2 is elevated as respiratory compensation, hypoventilation that retains CO2. Compensation rarely fully corrects pH, so a near-normal pH with abnormal CO2 indicates a mixed disorder or full compensation.
Traps
- Confusing osmolarity with tonicity.
- Assuming all edema means fluid excess when it can reflect low oncotic pressure.
- Calling a near-normal pH normal when both CO2 and HCO3 are abnormal.
- Explaining symptoms without linking them to the affected organ system.