A fall in Glomerular Filteration Rate (GFR) activates
The rate at which kidneys filter blood is called the glomerular filtration rate. The juxtaglomerular apparatus is located near the vascular pole of the glomerulus and its main function is to regulate blood pressure and the filtration rate of the glomerulus.
The secretion of renin is stimulated by the following three factors: When a fall in arterial blood pressure is detected by pressure sensitive receptors (baroreceptors) in the arterial vessels. When a decrease in sodium chloride (salt) is detected in the kidney by the macula densa in the juxtaglomerular apparatus.