Other factors affecting Glomerular filtration rate
Renal cells produce a battery of chemicals, many of which act as paracrines (local signaling molecules) :
- Prostaglandin E2 (PGE2) : The vasodilatory paracrine PGE2, counteracts vasoconstriction by norepinephrine and angiotensin II within the kidney. The adaptive value of these opposing actions is to prevent renal damage while responding to body demands to increase peripheral resistance
- Intrarenal angiotensin II : Although we usually think of angiotensin II as hormone, the kidney makes its own, locally acting angiotensin II that reinforces the effects of hormonal angiotensin II, It also dampens the resulting renal vasoconstriction by causing PGE2 release.
- Adenosine : Adenosine can be released as such or produced extracellularly from ATP released by macula densa cells. Although it functions as avasodilator systemically, adenosine constricts the renal vasculature
Abnormally low urine output (less than 50 ml/day), called anuria, may indicate that glomerular blood pressure is too low to cause filtration. However, renal failure and anuria can result from situations in which the nephrons cease to functions for a variety of other reason, including acute nephritis, transfusion reactions and crush injuries.