Glomerular filtration and autoregulation plateau

Glomerular filtration emerges from Starling forces and is held flat by tubuloglomerular feedback. Across renal perfusion 80–180 mmHg the engine holds GFR ≈ 125 mL/min (P_GC 54 mmHg, renal blood flow 1100 mL/min) while the open-loop control is not flat. Autoregulation is the kidney's R19 control-loop class. Grade [V]; absolute GFR [L].

Filtration is the Starling balance GFR = K_f·(P_GC − P_BS − π_GC). Tubuloglomerular feedback adjusts afferent resistance to hold GFR ≈ 125 mL/min across a wide perfusion range; with the loop open, GFR tracks pressure instead of plateauing.

Filtration set by Starling forces

The kidney is the control-loop class. Single-nephron filtration is the net Starling drive across the glomerular membrane times the filtration coefficient K_f.

Tubuloglomerular feedback is the plateau

A PI feedback on afferent arteriolar resistance senses distal flow and corrects it, holding GFR ≈ 125 mL/min (P_GC 54 mmHg, RBF 1100 mL/min) as perfusion swings 80–180 mmHg. The contrast test confirms the open-loop coefficient of variation is several-fold larger — the plateau is the feedback, not a passive property.