Renal - Physiology (Basic Concepts) Flashcards
Pg. 525-527 in First Aid 2014 Pg. 480-482 in First Aid 2013 Sections include: -Fluid compartments -Glomerular filtration barrier -Renal clearance -Glomerular filtration rate (GFR) -Effective renal plasma flow -Filtration -Changes in glomerular dynamics -Calculation of reabsorption and secretion rate -Glucose clearance -Amino acid clearance
What percentage of total body weight (kg) is total body water (L) versus nonwater mass?
60% total body water (L); 40% nonwater mass
Of total body water, what portion is extracellular versus intracellular fluid?
1/3 extracellular fluid; 2/3 intracellular fluid
What are the main extracellular fluid compartments? What portion of extracellular fluid is each?
Plasma volume - 1/4; Interstitial volume - 3/4
What is the major intracellular ion?
K+; Think: “HIKIN’ = HIgh K INtracellular”
What is the way to remember the % of body weight that applies to total body water, extracellular fluid, and intracellular fluid?
60-40-20 rule (% of body weight): 60% total body water, 40% ICF, 20% ECF
How is extracellular volume measured? How is plasma volume measured?
Extracellular volume measured by inulin; Plasma volume measured by radiolabeled albumin
What is the osmolarity (of plasma)?
290 mOsm/L
According to what 2 properties does the glomerular filtration barrier manage filtration?
Responsible for filtration of plasma according to size and net charge
What are the components of the glomerular filtration barrier? Where applicable, relate a component’s purpose to the overall function of the glomerular filtration barrier.
Composed of: (1) Fenestrated capillary endothelium (size barrier) (2) Fused basement membrane with heparan sulfate (negative charge barrier) (3) Epithelial layer consisting of podocyte foot processes
Which component of the glomerular filtration barrier acts to filter plasma according to size?
Fenestrated capillary endothelium (size barrier)
Which component of the glomerular filtration barrier acts to filter plasma according to charge?
Fused basement membrane with heparan sulfate (negative charge barrier)
What is lost in nephrotic syndrome? What are 4 associated consequences?
The charge barrier (of the glomerular filtration barrier) is lost in nephrotic syndrome, resulting in albuminuria, hypoproteinemia, generalized edema, and hyperlipidemia
What is renal clearance? Define it in both words and as a formula.
Cx = UxV/Px = volume of plasma from which the substance is completely cleared per unit time; (Note: Cx = clearance of X [mL/min], Ux = urine concentration of X (mg/mL), Px = plasma concentration of X, V = urine flow rate)
Give the fate of the substance x in the following scenarios: (1) Cx < GFR (2) Cx > GFR (3) Cx = GFR.
(1) Net tubular reabsorption of X (2) Net tubular secretion of X (3) No net secretion or reabsorption
What can be used to (accurately) calculate glomerular filtration rate (GFR), and why?
Inulin clearance can be used to calculate GFR because it is freely filtered and is neither reabsorbed nor secreted
What is the limitation of creatinine in terms of measuring GFR?
Creatinine clearance is an approximate measure of GFR. Slightly overestimates GFR because creatinine is moderately secreted by the renal tubules
What is a normal GFR?
100 mL/min
What is the clearance equation that equals GFR? What is another equation that can be used to define GFR?
GFR = U inulin x V/P inulin = C inulin; GFR = Kf [(Pgc - Pbs) - (PIgc - PIbs)] (Note: gc = glomerular capillary, bs = Bowman’s space, PI = mathematical pi, P = hydrostatic pressure, PI = oncotic pressure).
Again, what is the (Starling’s force) equation used to define GFR? Which component of this equation is normally zero?
GFR = Kf [(Pgc - Pbs) - (PIgc - PIbs)] (Note: gc = glomerular capillary, bs = Bowman’s space, PI = mathematical pi, P = hydrostatic pressure, PI = oncotic pressure); PIbs normally equals zero
What defines the stages of chronic kidney disease?
Incremental reductions in GFR define the stages of chronic kidney disease
What can be used to estimate effective renal plasma flow, and why?
ERPF can be estimated using PAH clearance because it is both filtered and actively secreted in the proximal tubule. All PAH entering the kidney is excreted.
What is the clearance equation that equals effective renal plasma flow?
ERPF = U pah x V/ P pah = C pah
How does renal blood flow relate to renal plasma flow?
RBF = RPF/(1-Hct)
How well does ERPF estimate true RPF?
ERPF underestimates true RPF by ~10%.
What is the equation for filtration fraction (FF)? What is a normal FF?
FF = GRF/RPF; 20%
What is the equation for filtered load?
Filtered load = GFR x plasma concentration
With what can GFR be estimated?
GFR can be estimated with creatinine clearance
With what is RPF best estimated?
RPF is best estimated with PAH clearance
Create a visual labeling the following: (1) Proximal convoluted tubule (2) Parietal layer of glomerular capsule (3) Afferent arteriole (4) Juxtaglomerular cells (5) Efferent arteriole.
See p. 481 in First Aid for visual
Which renal arteriole do prostaglandins affect? What are their effects on RPF, GFR, and FF? What blocks their effects?
Prostaglandins dilate afferent arteriole (increase RPF, increase GFR, so FF remains constant); NSAIDs
Which renal arteriole does Angiotensin II preferentially affect? What are its effects on RPF, GFR, and FF? What blocks its effects?
Angiotensin II preferentially constricts efferent arteriole (decrease RPF, increased GFR, so FF increases); ACE inhibitor
What do NSAIDs versus ACE inhibitors block?
NSAIDs block prostaglandins (which dilate afferent arteriole to increase RPF, decrease GFR, so FF remains constant); ACE inhibitors block Angiotensin II (which preferentially constricts efferent arteriole to decrease RPF, increase GFR, so FF increases)
What is the effect of afferent arteriole constriction on: (1) RPF (2) GFR (3) FF (GFR/RPF)?
(1) Decrease (2) Decrease (3) NC
What is the effect of efferent arteriole constriction on: (1) RPF (2) GFR (3) FF (GFR/RPF)?
(1) Decrease (2) Increase (3) Increase
What is the effect of increased plasma protein concentration on: (1) RPF (2) GFR (3) FF (GFR/RPF)?
(1) NC (2) Decrease (3) Decrease
What is the effect of decreased plasma protein concentration on: (1) RPF (2) GFR (3) FF (GFR/RPF)?
(1) NC (2) Increase (3) Increase
What is the effect of constriction of ureter on: (1) RPF (2) GFR (3) FF (GFR/RPF)?
(1) NC (2) Decreased (3) Decreased
Again, what is the equation for filtered load? What is the equation for excretion rate?
Filtered load = GFR x Px; Excretion rate = V x Ux
How is reabsorption versus secretion calculated/defined?
Reabsorption = filtered - excreted; Secretion = excreted - filtered
What is the fate of glucose at a normal plasma level (once filtered into the renal tubules)? What is the mechanism by which this occurs?
Glucose at a normal plasma level is completely reabsorbed in proximal tubule by Na+/glucose cotransport
What is the plasma glucose level threshold at which glucosuria begins? What is the level at which all transporters are fully saturated (Tm)?
At plasma glucose of ~160 mg/dL, glucosuria begins (threshold); At 350 mg/dL, all transporters are fully saturated (Tm)
For what condition is glucosuria an important clinical clue?
Diabetes mellitus
What renal/urinary change does normal pregnancy cause, and why?
Normal pregnancy reduces reabsorption of glucose and amino acids in the proximal tubule, leading to glucosuria and aminoaciduria
What happens to amino acids in the renal tubule, where, and via what mechanism?
Sodium-dependent transporters in the proximal tubule reabsorb amino acids
What kind of disorder is Hartnup’s disease? What and where does it affect mechanistically?
Autosomal recessive disorder; Deficiency of neutral amino acid (e.g., tryptophan) transporters in proximal renal tubular cells and on enterocytes
What percentage of total body weight are each of the following fluid compartments: (1) Total body water (2) Extracellular fluid (3) Intracellular fluid (4) Plasma volume (5) Interstitial volume.
(1) 60% (2) 20% (3) 40% (4) 5% (5) 15%
What effects does Hartnup disease have?
Leads to neutral aminoaciduria and decreased absorption from gut –> results in pellagra-like symptoms
How is Hartnup disease treated?
Treat with high-protein diet and nicotinic acid
