Glomerular Filtration and Renal Blood Flow

Question 1

where does filtration of plasma into tubule occur?

filtration occurs across what?

arterioles control what

Answer 1

in glomerulus

across the capillary loops into Bowman’s capsule

arterioles on either side of lgomerulus control flow of plasma and lbood through filtration apparatus while regulating GFR

Question 2

___ cells secrete renin (___)

Answer 2

granular cells = JGA cells = specialized smooth muscle of afferent arteriol

renin = controls AG II production

Question 3

Describe factors affecting ultrafiltration

what creates the filtration filter

what is molecular size cut-off

smaller proteins are ___ after passing through the filtere

Answer 3

1) molecular size/weight of proteins = up to 60k daltons (smaller, easier to cross, more concentrated in filtrate)
2) slit membranes between podocytes and overlapping podocyte
3) cut off = 60,000 = lower than albumin size

reabsorbed and catabolized to constituent amino acids by tubular epith cells

Question 4

3 layers of glomerulus

Answer 4

1) endothelium = fenestrated = no slits; exclude circulating RBC
2) basal lamina = secreted by endothelial and podocytes = made of mucoproteins with acidic sugars + protein cores

negatively charged, so more negative charge much lower than expected filterability

3) podocytes = sheet of tubular epith cell = round cells with numeorus “feet” pedicells in endothelial cell

form slit membranes

Question 5

freely filtered substance has a filterability =

nonfiltered substance, filterability =

Answer 5

1

0

Question 6

defect in podocyte feet would lead to___

Answer 6

leaky and large proteins easily pass through

Question 7

3 factors influencing Starling forces

Answer 7

1) Pgc = hydrostatic pressure in glomerular capillary –> only force for filtration into tubule
2) back pressure at Bowman’s capsule (Pt) = filtrate only flow in narrow parts of tubule –> backpressure opposing filtration
3) osmotic force that would cause fluid to reverse opposite GFR (pigc)= opposing nnegative relative to glomerular capill pressure

no sosmotic pressure

Question 8

Starling force for GFR equation

define variables

Answer 8

GFR = K(ΔP) = K(P​gc -​ P​t—​ π​gc)​

Pgc = pressure that drives flow across glomerular capillary endothelium into tubule

Pt = filtrate flow in narrow tubule = back pressure opposing filtration

π​gc = net osmotic force across filtration = opposing, negative = oncotic pressure = colloid osmotic pressure = COP

Question 9

Typical magnitude for each Starling force

Answer 9

P​gc-​P​t-​π​gc=​ Net filtration pressure (NFP)

● P​gc​= 46 mmHg/Torr
● P​t​= 10 mmHg/Torr
● π​gc =​ 30 mmHg = colloid osmotic pressure = COP
● NFP=6mm Hg which is<1%of1ATM

Question 10

Typical magnitude of each Starling force and resultant NFP

How with so little pressure do we filter so much?

Answer 10

Pgc =46mm

Pt =10mm

πgc= 30mm

NFP = 6mm

_____

Low resistance + large surface area for filtration (1 m^2) = large constant K (how much fluid flow across glomerulus per unit time for each unit pressure= more efficient)

Question 11

What if when you are sleeping your BP drops to 85 from 100

What if when exercising BP goes from 100 –> 115?

How does Pgc change?

Answer 11

Pgc and GFR stays constant

Question 12

Process of autoregulation of GFR and RBF

Autoregulation is mediated by ____

if you have a short term drop in MAP, what happens to arteriole?

if you have incr in MAP, what happens to arteriole

Answer 12

changes in afferent arteriolar ton–> myogenic so intrinsic to smooth muslce

afferent dilate to restore Pgc, GFR, and RBF to normal values

afferent constricts

Question 13

Range over which autoregulation occurs?

Answer 13

MAP 75-150

Question 14

What is the renal solution to hypovolemia?

GFR maintained by ____

Answer 14

1) decr MAP
2) incr total peripheral resistance (TPR) to shunt blood flow to vital organs
3) decr Renal blood flow
4) afferent arteriole constricts, decr RBF, decr Pgc, decr GFR (good for CV bad for kidney b/c GFR changing)
5) efferent arteriole constricts (divertor), incr Pgc back to normal incr GFR, incr renal vascular resistance, decr RBF even more for diverting perfusion to other organs

GFR maintained coordinated constriction of afferent and efferent arterioles

Question 15

GFR is regulated to be relatively ___ in normal physiology

But in real life, GFR decr depend on severity of hypovolemia, but compared to RBF?

Answer 15

constant

GFR will decr somewhat but not as much as RBF;

RPF decr and RBF decr

filtration fraction, and πgc incr

Question 16

Mechanism of hemorrhage (decr MAP)

Answer 16

1) decr MAP
2) incr stim of arterial baroreceptor reflex
3) incr firing of renal symp nerve
4) incr constriction of afferent and efferent arterioles
5) decr RBF, GFR constant

Question 17

Renal prostaglandins produced by ____

Secreted in response to? and have what effect on renal arterioles?

Answer 17

renal interstitial cells located in kidney medulla between pyramids

angiotensin II and have LOCAL DILATORY EFFECT ON RENAL ARTERIOLES

Question 18

2 effects of dilatory renal prostaglandins

Answer 18

1) maintain adequate renal blood flow by blunting effect of Angiotensin II (vasoconstrictor) on renal arteriole (so RBF and GFR reductions not as severe as with pure vasoconstrictive baroreceptor and AGII)
2) PROTECT AGAINST ACUTE RENAL FAILURE IN HYPOVOLEMIA
3) selective for afferent arteriole for vasodilation to restore GFR to normal

Question 19

compare autoregulatory vs. baroreceptor response

Answer 19

Question 20

complete mechanism of renal response to hypovolemia

Answer 20

1) hypovolemia, decr MAP

2)

a) stim of arterial baroreceptor reflex –> incr firing rate of renal symp nerve
b) (HORMONAL = incr JGA baroreceptor stim –> incr JGA renin secretion –> incr AGII)
c) intrarenal baroreceptors on granular cells
4) constriction of afferent/efferent arterioles (and incr TPR to restore MAP). decr RBF
5) Pgc constant and (decr renal blood flow –> incr filtration fraction –> incr πgc)
6) modest to moderate decr GFR

JGA cells on afferent arteriole stim by renal symp nerve –> secrete renin

Question 21

podocyte feet slit membranes and basal lamina CONTRIUBTE to

Answer 21

molecular sieving properties in glomerulus

Question 22

glomerular capillaries covered by ___

mesangial cells contact, decreasing

Answer 22

mesangial cells

area and decr K and decr GFR

Question 23

GFR is regulated to be relatively ___

tubular handling of each regulated substance is __

what happens when GFR constant but rate of water reabsorption decr

Answer 23

constant in normal physiology

varied

incr urine output

Question 24

capillary blood pressures are low compared to ___

if MAP incr by 15% will cause what changes in NFP and GFR

changes in MAP ___ proportionate changes in glomerular capillary pressure

Answer 24

MAP because blood has to flow thru major arteries before reaching capillaries

NFP double, GFR to 0

DO NOT CAUSE

Question 25

WITH AN UNCOMPENSATED incr in MAP what happens

Answer 25

afferent arteriole will contract and get bigger smooth muscle size to narrow tube

to keep PGc, GFR, RBF

Question 26

Malignant hypertension occurs when ____

Answer 26

MAP incr beyond autoregulatory range (> 150) incr PGc, incr GFR, incr RBF

Question 27

for a drop in MAP, the autoregulatory response vs. baroreceptor response

therefore,

Answer 27

autoregulatory response = dilate afferent arteriole

baroreceptor response in hypovolemia = constriction

baroreceptor > autoregulatory

Question 28

stim angiotensin II

Answer 28

constriction all arterioles, incr central perfusion and central pressure

Question 29

As the plasma travels down vessel,

define filtration equilibrium

Answer 29

constantly losing water to filtration and losing blood pressure from resistance of capillary

NFP is constantly decr along capillary length –> possible that NFP = 0 before plasma exits capillary