Final answer:
The macula densa cells detect increased delivery of Na+ , Cl− , and water when the GFR is above normal and the tubuloglomerular feedback begins.
Step-by-step explanation:
The macula densa cells detect increased delivery of Na+ , Cl− , and water when the GFR is above normal and the tubuloglomerular feedback begins. The macula densa cells are specialized cells located in the terminal portion of the ascending loop of Henle, and they monitor the concentration of Na+ in the fluid flowing through the distal convoluted tubule (DCT). When there is increased delivery of Na+ , Cl− , and water, the macula densa cells release ATP and adenosine, which act as paracrine factors to stimulate the myogenic juxtaglomerular cells of the afferent arteriole to constrict, reducing the glomerular filtration rate (GFR).
The macula densa cells detect increased delivery of Na+ , Cl− , and water when the GFR is above normal and the tubuloglomerular feedback begins. They release ATP and adenosine, which stimulate the myogenic juxtaglomerular cells of the afferent arteriole to constrict, reducing the GFR.