This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Renal physiology, Subject name: Physiology
[{'content': 'All are true about macula densa except \nSelect and explain. \nA. Sensor for glomerulotubular balance, B. The Na+ and Cl- enter the macula densa cells the Na-K-2Cl cotranspoer in their apical membranes, C. Increased formation and release of adenosine in macula densa cells, D. Causes vasoconstriction of afferent aeriole', 'role': 'user'}, {'content': 'Answer: A \nExplanation: This mechanism involves a feedback loop in which the concentration of NaCl in the tubular fluid is sensed by the macula densa of the juxtaglomerular apparatus and conveed into a signal or signals that affect afferent aeriolar resistance and thus the GFR. When the GFR increases and causes in the tubular fluid at the macula densa to rise, more NaCl enters the macula densa cells. This leads to an increase in the formation and release of ATP and adenosine, a metabolite of ATP, by macula densa cells, which causes vasoconstriction of the afferent aeriole. Vasoconstriction of the afferent aeriole returns the GFR to normal levels.', 'role': 'assistant'}]