Nephron

This simple model of the nephron shows how it folds back on itself so that the macula densa (blue) can communicate back to the juxtaglomerular apparatus and modulate the RAS system when volume is sensed to be inadequate. In other words, when the macula densa in the distal convoluted tubule detects low flow, it tells the RAS system to raise blood pressure and volume, in part by stimulating aldosterone. The aldosterone then interacts with the kidney even more distally, in the distal collecting system, and increases sodium absorption.