Expansion
Myogenic response and tubuloglomerular feedback
Expansion
Myogenic mechanism
- A rise in perfusion pressure stretches the afferent arteriole
- Stretch opens mechanosensitive channels, causing constriction
- Fast, acting within seconds
Tubuloglomerular feedback
- The macula densa, in the wall of the distal tubule where it passes the glomerulus, senses sodium chloride delivery
- Increased delivery, implying an excessive GFR, releases adenosine, which constricts the afferent arteriole and reduces GFR
- Reduced delivery releases renin, activating angiotensin II and constricting the efferent arteriole
- Slower, acting over 10 to 60 seconds
The two work together and hold GFR nearly constant between mean pressures of about 80 and 180 mmHg, which prevents wide swings in fluid and electrolyte excretion with ordinary changes in blood pressure.
Loop diuretics inhibit the macula densa sodium-potassium-2-chloride transporter, which blocks tubuloglomerular feedback and contributes to their potency.