Fluids, Filtration Flashcards
What % of body mass is total body water?
60%
What fraction of total body water is extracellular? Ie, what % of total body mass is extracellular fluid?
1/3
1/3 * 60% = 20% of total body mass.
What fraction of total body water is intracellular? Ie, what % of total body mass is intracellular fluid?
2/3
2/3 * 60% = 40% of total body mass.
What can radiolabeled albumin measure?
plasma volume
What can inulin measure?
extracellular volume
What is normal osmolality?
285-295 mOsm.
Of extracellular fluid, what % is interstitial fluid, and what % is plasma volume?
75% interstitial, 25% plasma.
What does the glomerular filtration barrier filter plasma according to?
Size and net charge.
What are the three components of the glomerular filtration barrier?
Fenestrated capillary endothelium
Fused basement membrane with heparan sulfate
Epithelial layer consisting of podocyte foot processes.
Which component of the glomerular filtration barrier is the size barrier?
Fenestrated capillary endothelium
Which component of the glomerular filtration barrier is the charge barrier?
Fused basement membrane w/ heparan sulfate
Which barrier is lost in nephrotic syndrome?
Charge barrier. Leads to albuminuria, hypoproteinemia, hyperlipidemia, edema etc.
What do podocytes wrap around?
Glomerular capillaries.
Why can inulin be used to calculate GFR?
It is freely filtered and neither reabsorbed nor secreted.
What is used clinically to calculate GFR?
Creatinine
Why is creatinine an imperfect measure of GFR?
Creatinine is mildly secreted by renal tubules
Does creatinine overestimate or underestimate GFR?
Overestimates, because the renal tubules are secreted - adding to the “cleared” number.
What can be given to make creatinine a more accurate measure?
Cimetidine. It decreases tubular secretion of Cr.
What does (Ux * V)/Px describe?
Clearance; volume of plasma from which the substance is completely clear per unit time.
If Cx > GFR, what does that mean?
Net tubular secretion of X.
If Cx < GFR, what does that mean?
Net tubular reabsorption of X.
What is used to measure effective renal plasma flow?
para-aminohippuric acid (PAH). PAH is both filtered AND secreted in the PCT, resulting in near 100% excretion.
What is the difference between GFR and effective renal plasma flow, conceptually?
Inulin measures what gets through the filtration barrier and assumes no action beyond that; this measures GFR.
PAH measures what gets through the filtration barrier and what is excreted from the blood - it is a more accurate measure of excretion.
What is the equation for effective renal plasma flow?
Same as clearance, using PAH:
(Upah * V)/Ppah
How does effective renal plasma flow relate to renal blood flow?
RBF= RPF /(1-Hct)
How the heck does the eRPF to RBF formula make sense?
Rearrange!
RBF * (1-Hct) = RPF
RBF - RBF(Hct) = RPF
Renal blood flow - (% that is RBCs) = Renal plasma flow
Is calculated eRPF accurate?
It underestimates by 10% - eRPF is actually 90% of RPF.
What is filtration fraction?
GFR/RPF
What is filtration fraction conceptually?
Of the amount that is flows through kidney, what percent came through the glomerulus.
What actions do NSAIDs have on renal arterioles?
Blocks dilation of the afferent arteriole.
What effect does afferent arteriole constriction have on GFR, RPF, and FF? (NSAIDs)
GFR and RPF decrease, FF is constant.
NSAIDs
What actions do ACEis have on renal arterioles?
Blocks constriction of the efferent arteriole.
What effect does efferent arteriole constriction have on GFR, RPF, and FF?
Increases the GFR, and decreases the RPF. FF increases.
ACEIs decrease GFR, increase RPF, FF decreases.
What effect does an increase in plasma protein have on GFR, RPF, and FF?
Decreases GFR and FF (increased oncotic pressure keeping things in the capillaries). No change on RPF.
What effect does a decrease in plasma protein have on GFR, RPF, and FF?
Increases GFR and FF. No change in RPF.
What does GFR + Px represent?
Filtered load
What does Ux * V represent?
Excretion rate
What does Filtered-excreted =
Reabsorption
What does Excreted - filtered =
Secretion.
