Juxtaglomerular apparatus

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Schematic depicting how the RAAS works. Here, activation of the RAAS is initiated by a low perfusion pressure in the juxtaglomerular apparatus

The juxtaglomerular apparatus is a renal structure consisting of the macula densa, extraglomerular mesangial cells, and juxtaglomerular cells. It is found at the vascular pole.

[edit] Juxtaglomerular cell

Juxtaglomerular cells (JG cells, also known as granular cells) are the site of renin secretion.

The JG cells are found in the afferent arterioles of the glomerulus and 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.

[edit] Macula densa

The macula densa senses fluid flow rate as well as sodium chloride concentration in the distal tubule of the kidney and secretes a locally active (paracrine) vasopressor which acts on the adjacent afferent arteriole to decrease GFR.

[edit] Mesangial cells

Mesangial cells regulate the blood flow in the glomerulus. They monitor the sodium and chloride levels in the distal convoluted tubules. If the amount of these ions is more, it will imply that the kidney does not have enough time to reabsorb or GFR (glomerular filtration rate) is too high. They communicate with the afferent arteriole and will cause vasoconstriction; decreasing the blood flow, subsequently decreasing the GFR.

[edit] External links

• Histology at BU 16010loa
• Diagram at Boston University

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