a complex consisting of (a) the juxtaglomerular cells, which are modified smooth muscle cells in the wall of the afferent glomerular arteriole and sometimes also the efferent arteriole; (b) extraglomerular mesangium (lacis cells), which are located in the angle between the afferent and efferent glomerular arterioles; (c) the macula densa of the distal tubule; and (d) granular epithelial peripolar cells located at the angle of reflection of the parietal to the visceral capsule of the renal corpuscle; provides feedback control of extracellular fluid volume and glomerular filtration rate by activating the renin-angiotensin system. SYN: j-g complex, juxtaglomerular apparatus.