Berne and Levy Ch. 32 Elements of Renal Function Flashcards
Properties of molecules that are freely filtered
Radius smaller than 20A, neutral
Properties of unfiltered molecules
Radius larger than 42A, negative
Properties of variously filtered molecules
Radius between 20-42A
Filtration fraction
GFR/RPF (usually 15-20%)
For any given molecular radius, __________ molecules are more readily filtered than __________ molecules
cationic; anionic
What is the only Starling force that favors filtration?
Pgc (glomerular capillary hydrostatic pressure)
What two forces oppose filtration?
Pbc and glomerular oncotic pressure
Ultrafiltration pressure at afferent end
17mmHg
ultrafiltration pressure at efferent end
8mmHg
What happens to Pgc along the length of the capillary?
DECREASES slightly (due to resistance to flow)
What happens to glomerular capillary oncotic pressure (pi gc) along the length of the capillary?
INCREASES (water is filtered out so protein conc increases in the capillary)
What is Kf?
ultrafiltration coefficient = the product of the intrinsic permeability of the glomerular capillary and the glomerular surface area available for filtration
Why is the rate of glomerular filtration so much greater in glomerular capillaries than in systemic capillaries?
the Kf is 100x greater in glomerular capillaries
Pgc is 2x greater as hydrostatic pressure in systemic caps
What happens to GFR with an INCREASE in afferent arteriole resistance?
decreases (because Pgc decreases)
What happens to GFR with a DECREASE in afferent arteriole resistance?
increases (Pgc increases)
What happens to GFR with an INCREASE in efferent arteriole resistance?
increases (Pgc increases)
What happens to GFR with a DECREASE in efferent arteriole resistance?
decreases (Pgc decreases)
Increase blood pressure has a transient ________ on Pgc and GFR
increase
What two mechanisms are responsible for autoregulation of RBF and GFR?
1) Myogenic mechanism
2) Tubuloglomerular feedback
What is the myogenic mechanism of autoregulation?
tendency of smooth muscle to contract when stretched (renal afferent arteriole constricts when stretched by high blood pressure)
What is the tubuloglomerular feedback mechanism in autoregulation?
concentration of NaCl is sensed by macular densa of JGA and converted into signals that affect afferent arteriolar resistance and GFR
When more NaCl is sensed (higher GFR), macula densa cells release ATP and adenosine which causes vasoconstriction of afferent arteriole (decrease flow)
Macula densa releases ___ as a vasodilator, attenuating tubuloglomerular feedback and ____________ enhancing it
NO; angiotensin II
When does autoregulation fail?
arterial pressures less than 90mmHg and in the presence of certain hormones/symp nerve activity
How do catecholamines (ep and norep) affect GFR?
act on alpha 1 receptors to vasoconstrict; DECREASE GFR
think, don’t need to pee when scared
What effect does angiotensin II have on GFR?
DECREASES it; vasoconstricts arteries
What two molecules counteract sympathetic vasoconstriction?
Prostaglandins (during hemorrhage) and NO (and Bradykinin via NO)
What effect does adenosine have on renal flow and why is it special?
VASOCONSTRICTS (normally vasodilates systemically)
