Afferent arterioles

The afferent arterioles are a group of blood vessels that supply the nephrons in many excretory systems. They play an important role in the regulation of blood pressure as a part of the Tubuloglomerular feedback mechanism.

The afferent arterioles branch from the renal artery, which supplies blood to the kidneys.

The afferent arterioles later diverge into the capillaries of the glomerulus.

Regulation
When renal blood flow is reduced (indicating hypotension) or there is a decrease in sodium and chloride ion concentration, the macula densa of the distal tubule releases prostaglandins, which cause the juxtaglomerular cells lining the afferent arterioles to release renin, activating the renin-angiotensin-aldosterone system, to increase blood pressure and increase retention of sodium ions via aldosterone.

The macula densa cell can also increase the local blood pressure of the afferent arterioles by increasing the synthesis of nitrous oxide or decreasing the synthesis of adenosine or ATP.

If the afferent arterioles are constricted then the blood pressure in the capillaries of the kidneys will drop.