explain the autoregulatory mechanism of GFR. in simple language

Kidneys maintain the glomerular filtration rate(GFR). This mechanism is auto regulative. This mechanism is carried out by juxtaglomerular apparatus. It regulates the renal blood flow and the gomerular filtration rate. When the GFR decreases the juxtaglomerular apparatus stimulates the cells to release renin. Renin activates the Renin angiotensin mechanism which helps to bring the GFR to normal level.