Juxtaglomerular apparatus
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The juxtaglomerular apparatus is a renal structure consisting of the macula densa and juxtaglomerular cells. Juxtaglomerular cells (JG cells) are the site of renin secretion.
The JG cells are found in the afferent arterioles of the glomerulus act as an intra-renal pressure sensor. Lowered pressure leads to secretion of renin which acts to increase systemic blood pressure via the renin-angiotensin system.
The macula densa senses fluid flow rate in the distal tubule of the kidney and secretes a locally active vasopressor which acts on the adjacent afferent arteriole to decrease GFR.