juxtaglomerulaire

The juxtaglomerular apparatus refers to a specialized structure in the nephron that regulates kidney function by coordinating glomerular filtration with systemic blood pressure. It consists of three components: the juxtaglomerular cells of the afferent arteriole, the macula densa region of the distal convoluted tubule, and extraglomerular mesangial cells (Lacis cells). This unit plays a central role in the regulation of the renin–angiotensin–aldosterone system and renal hemodynamics.

Juxtaglomerular cells are modified smooth muscle cells located in the wall of the afferent arteriole near the glomerulus. They synthesize and store renin and release it in response to decreased renal perfusion pressure, sympathetic nervous system activity (beta-1 adrenergic stimulation), and local signals from the macula densa and prostaglandins. Renin initiates the renin–angiotensin–aldosterone system by converting angiotensinogen to angiotensin I.

The macula densa consists of tall, densely packed cells at the end of the distal tubule adjacent to the afferent arteriole. It senses the composition and flow of tubular fluid, particularly NaCl concentration. When NaCl delivery is high, it promotes signals that reduce renin release; when NaCl delivery is low, it promotes renin release. Paracrine mediators involved in this signaling include adenosine, nitric oxide, and prostaglandins, which influence both renin secretion and arteriolar tone.

Extraglomerular mesangial cells (Lacis cells) form a signaling interface between the macula densa and the juxtaglomerular cells, aiding coordination of the tubuloglomerular feedback mechanism.

Clinical relevance: The juxtaglomerular apparatus is central to blood pressure regulation through the RAAS. Pharmacologic agents that target renin, angiotensin-converting enzyme, or angiotensin II receptors affect JGA signaling and are used to treat hypertension and kidney disease. Dysregulation of the JGA can contribute to hypertensive and renal pathologies.