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

12. Glomerular Function Flashcards by Priyanka Barad

what are the 3 layers of the glomerular filtration barrier

capillary endothelium
glomerular basement membrane
podocyte epothelium

(Blood –> urine)

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what is the glycocalyx and how does it contribute to filtration

= sticky biogel in the glomerular endothelial lumen

leads to net (-) charge –> repel (-) molecules

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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

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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

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what can be freely filtered

< 20 A

h2o

small solutes (glu, AA, electrolytes)

concentrations on either side of the membrane will be equal

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what CANNOT be freely filtered

> 42 A

large molecules (proteins)- RBC, WBC

formed elements (cells)

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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

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if excretion > filtration…

then tubular secretion must have occured

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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)

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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

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what is renal clearance

C = rate at which substance removed from plasma completely by the kidneys

C = ^Ux*V/_Px

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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

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what does glomerular filtration rate depend on

starlings forces

capillary filtration coeefficient (Kf) = permeabilty * SA

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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

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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 π_c

so on efferent side you favor tubular reabs

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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)

U_E = Ux * V

filter load - U_E = 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

U_In * V = P_In * GFR –> GFR = ^{U_In * 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

P_GC & π_BC

(π_BC should = 0 bc protein shouldnt be filtered)

what forces oppose filtration

P_BC & π_GC

how do you calculate net filtration P

P_GC - P_BC - π_GC

rmr π_B_C should = 0

what 3 factors contribute to GFR & how do you use these to calculate GFR

1. hydraulic conductivity (permeability) = **L_p** 2. SA for filtration = **S_f** 3. capillary ultrafiltration P = **P_UF** ultrafiltration coefficient = **K_f** = S_f\* L_p **==\> GFR = K_f\* P_UF**

P_UF can changed based on P_GC. What determines P_GC

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

1. **constrict afferent** arteriole --\> decrease P_GC & _decrease RBF_ 2. **dilate efferent** arterioles --\> decrease P_GC & _increase RBF_

what starling forces would lead to increased GFR? & how would each affect RBF

1. **dilate afferent** arterioles - increase P_GC & _increase RBF_ 2. **constrict efferent** arterioles - increase P_GC & _decrease RBF_

vasoconstrictor list =

1. angiotensin II 2. ATP/adenosine 3. endothelin 4. sympathetics (catecholamines)

vasodilators list =

1. Prostoglandins 2. Bradykinin 3. NO 4. ANPs 5. DA 6. 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 1. **change P** --\> increase oncotic P in efferent arterioles & PTC --\> increase Na reabs 2. **increase delivery of solute to PCT** --\> increased filter load --\> lot of co-transport of Na into PCT --\> increased Na reabs 3. **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