Structure of the Juxtaglomerular Apparatus

The juxtaglomerular apparatus is formed by the afferent and efferent arterioles of the glomerulus, the polar cushion (Polkissen), and a portion of the distal convoluted tubule (macula densa). The cells of the nontubular portion of the juxtaglomerular apparatus may contain specific secretory granules (granular cells) or may not (agranular cells). Both types of cells contain fibrillar bundles resembling those of smooth muscle and therefore may be considered modified smooth muscle cells. The granules develop from crystalline protogranules in Golgi cisternae. The cells of the macula densa differ from other cells of the distal tubule. Among the differences are a basal Golgi system and less development of the infolded basal membranes. Numerous non-myelinated nerves have been seen in association with glomerular arterioles. Many of these show granulated vesicles consistent with an adrenergic function.