Renal Anatomy, Physiology and Pathophysiology
The Renal Anatomy, Physiology and Pathophysiology domain tests nephron function, glomerular filtration, hormone production, and the metabolic consequences of acute and chronic kidney disease that drive dialysis decisions.
Core rules
- The nephron sequence is glomerulus, proximal tubule, loop of Henle, distal tubule, collecting duct; the proximal tubule reabsorbs most filtered sodium, water, glucose and amino acids.
- Normal GFR is about 125 mL/min; filtration fraction is roughly 20%; afferent arteriolar dilation and efferent constriction raise intraglomerular pressure and preserve GFR.
- The kidney produces erythropoietin, renin and activated vitamin D, and regulates H+ and HCO3-; loss of these functions causes anemia, hypertension and metabolic acidosis.
- Dialysis indications are summarized as AEIOU: acidosis, electrolyte disturbance, intoxication, overload, uremia.
Worked example
A steady-state creatinine rises from 1.0 to 2.0 mg/dL. Because production is stable and clearance is inversely related, doubling of creatinine suggests roughly a 50% fall in GFR, not complete kidney failure. Confirm steady state, volume status and recent nephrotoxins before acting.
Traps
Do not read creatinine as GFR during non-steady-state AKI; do not confuse afferent dilation with efferent constriction; and do not label every CKD patient as dialysis-dependent.