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59 Cards in this Set
- Front
- Back
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What is ultrafiltration?
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Formation of fluid that is nearly free of protein as the result of effects of hydrostatic and oncotic pressure gradients
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What is diuresis?
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Increase in urine flow
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What is antidiuresis?
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reduction in urine flow; usually implies urine concentration
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What is osmotic pressure?
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Pressure arising from the presence of solute molecules free in solution
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What in oncotic pressure?
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The osmotic pressure resulting specifically from the presence of nonpermeable macromolecules (such as albumin in the plasma)
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Describe the renal vascular anatomy, starting with the interlobar arteries?
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Interlobar arteries extend toward cortex along columns of Bertin --> arcuate arteries --> interlobular arteries --> afferent arteries of the glomerui --> glomerular capillaries --> efferent arterioles
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What is renal blood flow (RBF)?
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The amount blood (including RBC's/hematocrit) that goes to the kidneys
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What is renal plasma flow (RPF)?
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RBF - cellular component of blood
RBF = RPF + Renal RBC flow RPF = RBF (1 - Hct) |
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The filtration processes of the kidneys are a function of what blood flow?
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RPF - since filtration occurs from only the plasma water component
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What is Glomerular filtration?
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The filtration of plasma across the glomerular filtration barrier
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RBF affects what?
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GFR, renal handling of solute and water, urine concentration, and O2 delivery
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What are the 3 components of the glomerular filtration barrier?
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1. Endothelial cells of the glomerular capillaries
2. Glomerular Basement membrane 3. Podocyte and slits |
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When we refer to "kidney function" what do we usually mean?
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GFR
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The first step in urine formation is what?
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Filtration from plasma across the glomerular filtration barrier
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Wrt to size, what molecules are permeable to the glomerular membrane?
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Small ones
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Which charged molecules have a tougher time getting through the glomerular membrane?
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Negatively charged molecules
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What are the 2 forces that drive filtration of fluid out of the capillary, into bowman's capsule?
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1. Capillary hydrostatic pressure
2. Bowman's space oncotic pressure |
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What are the 2 forces that oppose filtration?
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1. Bowman's space hydrostatic pressure
2. Capillary Oncotic Pressure |
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What is the mathmatical equation for GFR?
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GFR = Kf [(Pgc-Pbs} - (πGC - πBS)]
Kf - ultrafiltration coefficient Pgc - hydrostatic pressure in glomerular capillary Pbs - hydrostatic pressure in bowmans πGC - oncotic pressure in glomerular capillary πBS - oncotic pressure in Bowman' space |
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How do the forces along the capillary length change from afferent to efferent arteriole?
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Pgc / Pbs / πBS stay constant
πGC increase slightly |
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Why does πGC rise?
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Due to extraction of water by ultrafiltration across filtration barrier
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What does Kf represent?
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1. Hydraulic permeability of the membrane
2. Effective membrane surface area |
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What vessels make the largest contribultion to total renal resistnace?
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Afferent and efferent arterioles
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What is the major determinant of renal blood, plasma flow, and GFR?
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Afferent and efferent arteriolar resistance
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What will be the effect of a decrease in afferent arteriolar tone of filtration across the glomerular capillaries?
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GFR will increase because of increased blood flow into the glomerulus
Recall: Hose - balloon - hose analogy |
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What will be the effect of an increase in efferent arteriolar tone on filtration across the glomerular capillaries?
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GFR will increase - more pressure in the glomerular capillary
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How does increasing afferent arteriolar resitance affect the RPF and GFR?
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Decreases them due to decreased intraglomular pressure
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What is the effect of increasing effererent arteriolar resitance on RPF and GFR?
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RPF declines
GFR increases --> then decreases because falling RPF dominates |
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What are 2 categoreis of factors that modulate RBF and GFR and where do they act?
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Vasoconstrictors - act on efferent arteriole (increase GFR)
Vasodilators - act on afferent arteriole (increase GFR) |
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What are 3 examples of vasoconstrictors that act on the kidney?
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1. AG II
2. Catecholamines (E/NE) 3. Endothelin |
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What are 2 examples of vasodilators that act on the kidney?
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1. Prostaglandins
2. ANP |
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What is special about the macula densa cells?
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Area where there is communication between lumen of DCT and the afferent arteriolar lumen
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Tuboglomerular feedback (TGF) describes what observation?
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Increases in flow past macula densa are followed by reduction in RBF and GFR
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What is the real signal for TGF?
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NaCl concentration
(higher flow reduces reabsorption in the thick ascending limb so delivers higher concentration to MD) |
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Wrt to kidney mass balance, what is Arterial Input equal to?
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Arterial Input = Venous output + urine output
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What is the mathematical equation for kidney solute mass balance?
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[Arterial Plasma of solute] x Arterial RPF (Arterial Input of solute) = [Venous Plasma of solue] x Venous plasma flow + [Urine of solute] x Urine flow rate
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The amount filtered of a solute is equal to what?
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(GFR)(Px)
Px - plasma concentration of solute "x" Note: only applies to a solute that is freely filtered |
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What compound is the ideal marker of GFR?
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Inulin - becuase inert, completely filtered, not secreted, and not reabsorbed
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How does the amount of inulin filtered compare to the amount of inulin excreted in the urine?
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They're equal
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What is the mathematical equation relating inulin filtration to urine output?
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P(In) x GFR = U(In) x Urine Volume
Rearrange --> GFR = U(In) x UrineVol / P(In) P(In) - serum concentration of inulin U(In) - urine concentration of inulin |
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Is inulin used routinely?
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No because expensive and has to be given continuously
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What is normally used in place of inulin?
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Creatinine - easy way to get close approximation of GFR
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What does UxV represent?
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(Urine Concentration of X) (Volume of urine flow)
Represents Urinary excretion Rate |
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What does PxCx represent?
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Plasma Removal Rate
(plasma concentration of X)(Constant that defines the clearance from the plasma of a solute resulting from the sum of (glomerular filtration + secretion - reabsorption) |
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What is the overall equation for clearance?
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Cx = (UxV) / Px
Cx - volume of plasma cleared of "x" per unit time (via ANY means) |
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In words, what does clearance tell us?
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The apparent volume of plasma that is totally cleared of a solute in a unit of time
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Does clearance tell anything about HOW the solute got into the urine?
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NOOOO
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What is fractional excretion?
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Basically clearance of "X" divided by GFR
Fraction of "X" that was filtered that appears in the urine - lets us compare secretion vs. reabsorption |
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What is the equation for fractional excretion?
Equation when using creatinine? |
(FEx) = (UxV) / [Px(GFR)]
Creatinine: FEx = (Ux/Px)/(Ucr/Pcr) |
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How does plasma creatinine relate to GFR?
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Plasma creatinine increases as GFR declines
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Creatinine clearance (CCr) is equal to what?
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CCr = GFR + TSCr
TSCr - tubular secretion of creatinine |
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Wrt to measure GFR, do we want a low or high amount of Tubular secretion of creatinine?
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Low
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How does the secretion of creatinine effect the measurements of GFR?
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Under normal conditions it doesn't
But under reduced GFR, secretion is larger making it a poorer measurement of GFR |
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Creatinine measurements usually do what to GFR measurements
Urea? |
Creatinine - overestimates due to secretion
Urea - underestimates due to resporption |
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What is the best measurement then of GFR?
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Averaging Creatinine and Urea
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Traditionally, what method was used to estimate GFR by creatinine clearance?
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24 hours urine collection
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What are used to get around the 24 hour urine collection?
What is the cockroft-gault formula: |
Estimating equations (see page 283)
CCr: (140-age)(kg weight) / (72)(Cr) x 0.85 in women |
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Is pure serum creatinine a good measure of kidney function?
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No - remember grandma and 20yo have same creatinine
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Can the creatinine be used to measure GFR if its levels are changing?
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NO
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