12. Glomerular Function Flashcards
what are the 3 layers of the glomerular filtration barrier
- capillary endothelium
- glomerular basement membrane
- podocyte epothelium
(Blood –> urine)
what is the glycocalyx and how does it contribute to filtration
= sticky biogel in the glomerular endothelial lumen
leads to net (-) charge –> repel (-) molecules
describe filterability based on charge/size
- neutral =
- cationic =
- anionic =
- neutral = as molecule gets larger, filterabilty decreases
- cationic = increase filterabilty even if its a larger size bc attraction of (+) charge
- anionic = decrease filterabilty bc glycocaylx repel (-) charge
what happens to filterabilty of anionic dextrans if there is nephrotoxic serum nephritis
barrier messed up - (-) charge removed
more anioinic substance can be filtered ==> proteinuria
what can be freely filtered
< 20 A
h2o
small solutes (glu, AA, electrolytes)
- concentrations on either side of the membrane will be equal
what CANNOT be freely filtered
> 42 A
large molecules (proteins)- RBC, WBC
formed elements (cells)
How do you calculate urinary excretion
glomerular filtration (Gf) - tubular reabs (Tr) + tubular secretion (Ts)
–> rearrange to solve for others = ex- tubular reabs = Gf - Ue + Ts
if excretion > filtration…
then tubular secretion must have occured
what goes in must come out so… equation to describe this =
arterial input = venous output + urine outpu
(Px,a * RPFa) = (Px,v * RPFv) + (Ux * V)
how do you calculate urine excretion rate
Ux * V
Ux = urinary [X] = [X]/urine vol
V = urine FLOW RATE = urine vol/time –> depend on fluid intake/homeostasis
normal = 0.4 mEq/min
what is renal clearance
C = rate at which substance removed from plasma completely by the kidneys
C = Ux*V/Px
what is glomerular filtrate
vol of plasma FILTERED across glomerular cap into bowmans space by BOTH kidneys per unit time
should be protein & cell free
aka- plasma ultrafiltrate & isosmotic
what does glomerular filtration rate depend on
starlings forces
capillary filtration coeefficient (Kf) = permeabilty * SA
how do you calculate filtration fraction
FF = GFR/RPF
= the fraction of RPF that is filtered across glomerulus
change w/ ultrafiltration P, influenced by BP
explain why - when FF inceases - oncotic P of efferent arteriole increases
& what is the result of this
as you move from afferent to efferent you filter h2o –> increase concentration in cap –> increase πc
so on efferent side you favor tubular reabs
compare filtered load & FF
filtered load = rate in mg/min = GFR * Px
FF = GFR/RBF
what % of filter load of X is reabs per day?
how do you calculate
filter load = GFR * Px (at glomerular cap)
UE = Ux * V
filter load - UE = reab
reabs/filter load = % reabs
when is GFR proportional to renal clearance
- = freely filtered
- ISNT reabs or secreted at renal tubule
- NOT synthesized, broken down or accumulated by kidney
- phys inert (not toxic & w/o effect on renal fxn)
normal GFR around 125 mL/min
what is inulin
= freely filtered, not reabs or secreted @ tubular level
so amount excreted = amount filtered
UIn * V = PIn * GFR –> GFR = UIn * V/PIn
what is creatinine clearance used for
long term monitoring of renal fxn
= endogenous, freely filtered, minimal secreted
but still used to measure GFR compared to inulin bc its endogenous
what 3 areas of the of kidney recieve sympathetic stimulation
what is the result
- arterial resistance vessels (alpha1) –> constrict afferent arterioles
- juxtaglomerular granular cells (beta1) - renin + RAAS
- tubular epithelial cells (alpha1) - Na/K ATPase- increase Na reabs
==> all lead to increased BP
what two forces favor filtratrion
PGC & πBC
(πBC should = 0 bc protein shouldnt be filtered)
what forces oppose filtration
PBC & πGC
how do you calculate net filtration P
PGC - PBC - πGC
rmr πBC should = 0
what 3 factors contribute to GFR
& how do you use these to calculate GFR
- hydraulic conductivity (permeability) = Lp
- SA for filtration = Sf
- capillary ultrafiltration P = PUF
ultrafiltration coefficient = Kf = Sf * Lp
==> GFR = Kf * PUF
PUF can changed based on PGC. What determines PGC
renal arterial BP
afferent arteriolar resistance
efferent arteriolar resistance
what are glomerular mesangial cells
cells with contractile properties - can change SA of endothelium available for filtration
what is hydrostatic P like as it passes from Renal A to Renal V
How can starling forces change to decrease GFR
& how do each affect RBF
- constrict afferent arteriole –> decrease PGC & decrease RBF
- dilate efferent arterioles –> decrease PGC & increase RBF
what starling forces would lead to increased GFR?
& how would each affect RBF
- dilate afferent arterioles - increase PGC & increase RBF
- constrict efferent arterioles - increase PGC & decrease RBF
vasoconstrictor list =
- angiotensin II
- ATP/adenosine
- endothelin
- sympathetics (catecholamines)
vasodilators list =
- Prostoglandins
- Bradykinin
- NO
- ANPs
- DA
- ACE-inhibitor
what does angiotensin II do primarily
constrict efferent arterioles –> increase GFR
(ACE-inhibitor stops this and decrease GFR)
what part of the renal system is innervated by sympathetics
renal blood vessels
local sym & circulating Epi/NE activate alpha1 (more on afferent than efferent arterioles)
what is glomerulartubular balance
& how is it achieved
= increasing reabs rate w/i renal tubules when GFR rises
- change P –> increase oncotic P in efferent arterioles & PTC –> increase Na reabs
- increase delivery of solute to PCT –> increased filter load –> lot of co-transport of Na into PCT –> increased Na reabs
- increase shear strain- bc increase GFR & flow –> upregulate Na transporter insertion –> increase Na reabs
what is local myogenic feedback reflex
btn vascular sm. m cells
blood vessels resist stretch during periods of high BP –> Sm. M in vessel contract
–> signal Ca –>
afferent arteriolar constriction & efferent dilation
what is tubuloglomerular feedback
macula densa -sense increased distal tubular NaCl –>
increase ATP/adenosine signaling –> bind thier receptor –>
relase intracell Ca –> stimulate granule cells & then mesangial cells –>
constrict afferent arterioles –> juxtaglomerular cells decrease secretion or renin –> decrease GFR
what is fractional excretion and how do you calculate it
% of whatever has been filters is actually excreted
=amount X excreted/amount X filtered
can assume GFR = clearance of creatinine for some substances
