Function of the Juxtaglomerular Apparatus: Control of Glomerular Hemodynamics and Renin Secretion

More than a century ago, Golgi observed that “the ascending limb of the loop of Henle returns with invariable constancy to its capsule of origin”. 1 At this point of contact at the glomerular hilum, the afferent and efferent arterioles together with the adherent distal tubule form a wedge-shaped compartment which contains the three defining cell types of the juxtaglomerular apparatus (JGA) ( Figure 23.1 ). The macula densa (MD) cells in the wall of the tubule abut on a cushion of closely packed interstitial cells called Goormaghtigh or lacis cells. These cells are indistinguishable in their fine structure from mesangial cells 2 and are also referred to as extraglomerular mesangial (EGM) cells. The third specialized cell type of the JGA is the juxtaglomerular granular (JG) cell, a modified smooth muscle cell in the media of the arteriolar wall.