Kidneys keep GFR steady by two local controls:
• Myogenic response – when blood pressure rises, afferent arteriole constricts; when BP falls, it dilates.
• Tubuloglomerular feedback (via JGA) – macula densa senses NaCl in filtrate; high NaCl → afferent constriction; low NaCl → renin release → RAAS activation → restores GFR.