Renal Physiology for UPSC CMS: GFR, RAAS, Acid-Base and the Equations Every Candidate Must Know

GFR#

Normal: 125 mL/min. Measured by inulin clearance (gold standard). Estimated by creatinine clearance or eGFR (CKD-EPI formula).

Creatinine clearance > GFR because of tubular secretion.

RAAS#

Renin (JG cells) -> Angiotensinogen -> Angiotensin I -> ACE (lung) -> Angiotensin II -> Aldosterone (zona glomerulosa).

Effects: Vasoconstriction (angiotensin II), Na+ retention + K+ excretion (aldosterone), Thirst + ADH (angiotensin II).

Concentrating Mechanism#

Countercurrent multiplier (Loop of Henle) + Countercurrent exchanger (vasa recta). ADH increases water reabsorption in collecting duct.