1. Which of the following is most likely to impair renal filtration and GFR?
a) Prostaglandin I2
2. Which of the following is NOT a mechanism by which GFR can decrease?
a) Renal tubular injury
b) Decreased muscle mass
c) Reduced Kf
d) Decreased renal blood flow
3. Which of the following is paired incorrectly with its site of action?
a) acetazolamide- proximal tubule
b) furosemide- loop of Henle
c) bumetanide- loop of Henle
d) hydrochlorothiazide- collecting duct
ANSWERS & EXPLANATIONS
1. D- ACE inhibitors such as enalapril inhibit angiotensin converting enzyme and thus impair the production of angiotensin II. Angiotensin II normally serves to vasoconstrict the efferent arteriole and thus improves filtration fraction and GFR.
2. B- decreased muscle mass may lead to a lower baseline creatinine value (conversely, increased muscle mass could be associated with a higher baseline creatinine value). However, this should not affect GFR. Renal tubular injury, decreased capillary ultrafiltration coefficient (Kf) and reduced renal blood flow all can lead to reduced GFR. In addition, backleakage of tubular ultrafiltrate into the renal intersititum is the other one of the 4 major mechanisms leading to reduced GFR.
3. D- hydrochlorothiazide acts at the distal tubule (Na-Cl transporter)