Sunday, May 15, 2011

Juxtaglomerular Apparatus

The juxtaglomerular apparatus is an anatomical unit located between the vascular pole of the renal corpuscle and the returning distal convoluted tubule of the same nephron. Named for its proximity to the glomerulus, the juxtaglomerular apparatus is a specialized region of a nephron where the afferent arteriole and the distal convoluted tubule come into direct contact with each other.

The juxtaglomerular apparatus regulates the function of each nephron, being involved in feedback control of renal blood flow and glomerular filtration rate. It is composed of three types of cells: 1) macula densa cells, which are columnar epithelium thickening of the distal tubule, sensing sodium chloride concentration in the distal tubule of the kidney and secreting a locally active (paracrine) vasopressor, which acts on the adjacent afferent arteriole to decrease glomerular filtration rate (GFR); 2) extraglomerular mesangial cells, which are structural cells in the glomerulus that under normal conditions serve as anchors for the glomerular capillaries; 3) juxtaglomerular cells, which are modified smooth muscle cells which produce renin.