NBME 7BLOCK 2....plz help. - usmle@va

[ArchivalUser]

Hi yeabiruh,for qno 39 could u pls explain about how the gfr is maintained.I thought when we constrict the efferent arteriole[angiotensin2] upstream preesure will increaseand that will lead to increased gfr.A-2 also causes decreased blood flow due to vasoconstriction.Finally ff should increase right?pls correct me if my concept is wrong.

[ArchivalUser]

hi nija.....when Angiotensin II is adminstered for 60 minutes it also vasoconstricts the renal aretries...causing a decrease in renal blood flow and subsequently decreased GFR from the base line...

---but to correct homeostasis ( to bring the GFR FROM decreased to the' pre AG II INFUSION LEVEL')Ag II then vasoconstricts THE efferent aretriole more than any vessel (including the renal arteries)....this causes the GFR to be close to the pre infusion level

---AG II constricts all arteries but to a greater extent the efferent arterioles

[ArchivalUser]

Hi yeabiruh thanx a lot for ur wonderful explanation.Now i got it.God bless.