Answer: The juxtaglomerular complex is a system that regulates the rate of filtrate formation and systemic blood pressure. This is made up of the distal convoluted tubule and the glomerular afferent arteriole. In the distal convoluted tubule, there are specialized epithelial cells (macula densa) that detect sodium concentration of the liquid in the tubule. Because of the increase in sodium, the macula densa cells activate the afferent arteriole’s contraction, which reduces blood flow in the glomerulus. In the afferent arteriole, there are juxtaglomerular cells which secrete renin when the blood pressure decreases.