An anatomical structure which consists of juxtaglomerular cells, extraglomerular mesangial cells and the macula densa. The juxtaglomerular apparatus lies adjacent to the glomerulus and regulates kidney function by maintaining the blood flow to the kidney and the filtration rate[GO]. a microscopic structure in the kidney, which regulates the function of each nephron. The juxtaglomerular apparatus is named for its proximity to the glomerulus: it is found between the vascular pole of the renal corpuscle and the returning distal convoluted tubule of the same nephron. This location is critical to its function in regulating renal blood flow and glomerular filtration rate. The three cellular components of the apparatus are the macula densa, extraglomerular mesangial cells, and juxtaglomerular cells (also known as granular cells)[WP]. [ http://amigo.geneontology.org/amigo/term/GO:0072206 http://en.wikipedia.org/wiki/Juxtaglomerular_apparatus ]