GFR/RBF Flashcards
PGC PBC piGC piBC And how much pressure exists from these forces?
Out of capillary into BC. (60)
Out of BC into the capillary. (18)
Out of BC into the capillary. (32)
Out of the capillary into the BC. (0)
Net filtration pressure =
PGC - PGC - piGC
What 3 factors contribute to GFR?
- Hydraulic conductivity (permeability of the fenestrated epithelium). (Lp)
- Surface area for filtration. (Sf)
- Capillary ultrafiltration pressure. (PUF)
GFR is the product of these 3 factors.
What is the main way to alter PUF?
How can you do that? (3)
Changing PGC.
Adjust renal arterial BP.
Afferent arteriolar resistance
Efferent arteriolar resistance
Ultrafiltration coefficient (Kf) =
Lp x Sf
hydraulic conductivity x surface area
What 2 sites in the renal vasculature are regulated? Why?
At the afferent and efferent arterioles, because there is the greatest change in hydrostatic pressures there.
How does the PGC and piGC change from the afferent arteriole to the efferent arteriole?
PGC goes down slightly as filtrate leaves the vasculature. As a result, the piGC increases due to an increase in plasma protein conc.
What happens to PGC, RBF and GFR when only the AFFERENT arteriole is constricted?
All 3 decrease. Less blood is perfusing the glomerulus (RBF), so GFR goes down, and therefore PGC is reduced.
What happens to PGC, RBF and GFR if only the EFFERENT arteriole is constricted?
PGC increases because of buildup of blood in the glomerulus. RBF decreases because less blood can leave the efferent arteriole. GFR increases initially with PGC, but then goes down as RBF dominates.
As compared to the brain on a per-gram basis, how much O2 do the kidneys use? How much blood flow?
Consume O2 at 2x the rate.
7x the amount of BF.
O2 consumption is related to:
The high rate of Na reabsorption in the tubules.
What sympathetic receptor is on renal vasculature? How is it distributed between afferent and efferent arterioles?
a1
More a1 on the afferent than the efferent arteriole.
Common vasoconstrictors (3):
Sympathetic nerves (catecholamines) Angiotensin II Endothelin
Common vasodilators (6):
PGE2, PGI 1, NO, Bradykinin, DA, ANP
Glomerular balance
Adjusts reabsorption rate within the renal tubules when GFR changes.
GFR inc, RR inc.
Link between filtered load and GFR
Direct relationship. The higher the GFR, the more normally filtered substances (Glc, AA, etc) are filtered (filtered load).
Autoregulation goal
Maintain RBF and GFR within narrow limits across wide ranges of BPs.
What 2 forces can increase resistance in renal vasculature?
Myogenic reflex (local reflex) Juxtaglomerular apparatus (tubuloglomerular feedback) as a physiological feedback.
What is the autoregulatory range?
80-170 mmhg
Local myogenic feedback reflex mechanism
BVs resist stretch during times of increased BP (increases resistance).
SM contraction and Ca signaling)
Afferent arteriolar constriction, efferent arteriole dilation.
Juxtaglomerular apparatus contains (3)
Macula densa cells
JG cells
Extraglomerular mesangial cells
Tubuloglomerular feedback mechanism (5)
Senses tubular NaCl conc.
Feeds back signal to adjust arteriolar resistance as needed.
Signals between macula densa cells and JG cells.
Maintains constant Na+ delivery to the DCT and constant GFR.
Releases renin.
Macula densa signaling during increased renal perfusion (4)
Increased delivery of NaCl to JG apparatus.
Increased ATP/adenosine
Vasoconstriction of the afferent arteriole (Ca signaling)
Decreased GFR
Macula densa signaling during decreased renal perfusion (3)
Macula densa signals to JG cells to secrete renin.
Results in efferent arteriolar vasoconstriction AND afferent arteriolar dilation, via NO.
Vasodilation of the afferent arteriole's effect on: RBF, GFR, peritubular capillary hydrostatic pressure PGs Bradykinin NO DA ANP
Increase
Increase
Increase
Vasoconstriction of the afferent arteriole’s effect on: RBF, GFR, peritubular capillary hydrostatic pressure
ACE inhibitors
Decrease
Decrease
Decrease
Vasodilation of the efferent arteriole’s effect on: RBF, GFR, peritubular capillary hydrostatic pressure
Sympathetics
Increase
Decrease
Increase
Vasodilation of the efferent arteriole’s effect on: RBF, GFR, peritubular capillary hydrostatic pressure
Angiotensin II
Decrease
Increase/no change
Decrease