Final answer:
Macula densa cells of the juxtaglomerular apparatus (JGA) regulate GFR through the tubuloglomerular feedback mechanism by monitoring sodium concentration and causing vasoconstriction or vasodilation of arterioles.
Step-by-step explanation:
The macula densa cells of the juxtaglomerular apparatus (JGA) regulate glomerular filtration rate (GFR) through the tubuloglomerular feedback mechanism. These cells monitor sodium concentration in the tubule, specifically in the terminal portion of the ascending loop of Henle. In response to changes in sodium concentration, the macula densa cells release paracrine signals, such as ATP and adenosine, which can cause vasoconstriction or vasodilation of the afferent and efferent arterioles.
When sodium concentration is high, the macula densa cells stimulate vasoconstriction of the arterioles, reducing blood flow into the glomerulus and decreasing GFR. On the other hand, when sodium concentration is low, the cells promote vasodilation of the arterioles, increasing blood flow and GFR.
This intrinsic mechanism helps regulate the GFR and maintain the balance of fluid and solutes in the body.