63: Filtration & Clearance Flashcards
GLOMERULAR FILTRATION is the process by which plasma is filtered across the glomerular capillaries to form a _______-free ultrafiltrate in Bowman’s space. Differences in the oncotic and hydrostatic pressure (Starling Forces) across the glomerular capillaries drive the net efflux of an ultrafiltrate from the plasma. With the exception of plasma protein, organic and inorganic anionic and cationic solutes are _____ filtered across the glomerular capillaries and exist in the _____ concentration in plasma and ultrafiltrate.
GLOMERULAR FILTRATION is the process by which plasma is filtered across the glomerular capillaries to form a protein-free ultrafiltrate in Bowman’s space. Differences in the oncotic and hydrostatic pressure (Starling Forces) across the glomerular capillaries drive the net efflux of an ultrafiltrate from the plasma. With the exception of plasma protein, organic and inorganic anionic and cationic solutes are freely filtered across the glomerular capillaries and exist in the same concentration in plasma and ultrafiltrate.
GLOMERULAR FILTRATION RATE (GFR) is approximately 125 ml/min or 180L per day, which is significantly more than the 3 to 4L of plasma filtered/day across other systemic capillaries to form interstitial fluid. Interstitial fluid or “systemic filtrate” is continuously returned to the vasculature via ______ drainage. The daily volume of glomerular filtrate is more than 10-fold the ______ fluid volume (14L/70Kg body weight) and equivalent to filtering the entire ECF volume every 2 hrs. This rapid turnover of ECF through the kidneys serves the purpose of maintaining ECF volume and solute composition within narrow limits by responding to correct changes ECF volume and solute composition.
GLOMERULAR FILTRATION RATE (GFR) is approximately 125 ml/min or 180L per day, which is significantly more than the 3 to 4L of plasma filtered/day across other systemic capillaries to form interstitial fluid. Interstitial fluid or “systemic filtrate” is continuously returned to the vasculature via lymphatic drainage. The daily volume of glomerular filtrate is more than 10-fold the extracellular fluid volume (14L/70Kg body weight) and equivalent to filtering the entire ECF volume every 2 hrs. This rapid turnover of ECF through the kidneys serves the purpose of maintaining ECF volume and solute composition within narrow limits by responding to correct changes ECF volume and solute composition.
Filtration Rate =
Filtration Rate = Kf [(PGC – PBS) – (piGC – piBS)]
Kf is the filtration coefficient of the glomerular capillary and is the product of the capillary hydraulic conductivity and the surface area available for filtration.
Know these 3 things that prevent passage of elements into the Bowman’s space:
- endothelial cells of glomerular capillaries restrict passage of cellular elements into ______ space.
- capillary ______ membrane restricts filtration of solutes. Proteoglycans have strong _____ charges favoring filtration of cations.
- visceral epithelial layer of Bowman’s capsule. Podocytes have foot process that cover glomerular capillaries. Foot processes separated by filtration slits connected by a thin diaphragm. Glycoproteins with ______ charges also cover podocytes, filtration slits and slit diaphragms favoring filtration of small _____ solutes.
Know these 3 things that prevent passage of elements into the Bowman’s space:
- endothelial cells of glomerular capillaries restrict passage of cellular elements into Bowmans space.
- capillary basement membrane restricts filtration of solutes. Proteoglycans have strong anionic charges favoring filtration of cations.
- visceral epithelial layer of Bowman’s capsule. Podocytes have foot process that cover glomerular capillaries. Foot processes separated by filtration slits connected by a thin diaphragm. Glycoproteins with negative charges also cover podocytes, filtration slits and slit
diaphragms favoring filtration of small cationic solutes.
Renin is released by ________ apparatus.
Renin is released by juxtaglomerular apparatus.
As we increase the size of the molecule, filterability _____ = not in bowmans space.
Cationic molecules are ____ easily filtered than neutral and anionic.
Smaller molecules are ______ easily filtered than larger ones.
Filterability = clearance ratio
Inulin is ______ filtered
The clearance ratio is a quantitative index of solute filterability relative to inulin, which is freely filtered. The ______ charge on the basement membrane and foot processes impedes the passage of _____ charged solutes (proteins) while allowing passage of neutral solutes and positively charged solutes.
As we increase the size of the molecule, filterability decreases = not in bowmans space.
Cationic molecules are more easily filtered than neutral and anionic.
Smaller molecules are more easily filtered than larger ones.
Filterability = clearance ratio
Inulin is freely filtered
The clearance ratio on the Y axis is a quantitative index of solute filterability relative to inulin, which is freely filtered. The negative charge on the basement membrane and foot processes impedes the passage of negatively charged solutes (proteins) while allowing passage of neutral solutes and positively charged solutes.
FF= ? = 125ml/min ~= 0.2 RPF 600 ml/min
Glomerular filtration rate
Renal plasma flow (RPF)
Filtration Fraction (FF)
FF=GFR/RPF
Thus, the kidney filters 180 L of plasma per day, which is more than 10-fold the ECF volume (14 L/70 Kg man). The kidneys serve to maintain constant volume and solute composition of the ECF (homeostasis) by acting upon the enormous volume and solute composition of the glomerular filtrate to form urine. GFR remains constant and the rate and volume of urine excreted varies according to the rate and volume of fluid consumed, which changes the volume and solute concentration of the ECF.
In acute renal faliure when there is __ blood flow, there is __ urine. Renal faliure = the absence of making urine.
If the kidneys are not filtering, they are not making any urine.
In acute renal faliure when there is no blood flow, there is no urine. Renal faliure = the absence of making urine.
If the kidneys are not filtering, they are not making any urine.
The rate of glomerular filtration _____ with the rate of plasma flow through the glomeruli, achieving a maximum GFR at a plasma flow of approximately 600 ml/min. As plasma flow increases through the glomeruli, an increasingly greater surface area of the glomerular capillaries begin filtering plasma until all the glomerular surface area is filtering plasma and a ______ rate of glomerular filtration is achieved.
The rate of glomerular filtration increases with the rate of plasma flow through the glomeruli, achieving a maximum GFR at a plasma flow of approximately 600 ml/min. As plasma flow increases through the glomeruli, an increasingly greater surface area of the glomerular capillaries begin filtering plasma until all the glomerular surface area is filtering plasma and a maximal rate of glomerular filtration is achieved.
See pg. 113
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GFR = ?
GFR = Us x V/Ps
Exogenous Inulin (IV fructose polymer) & Endogenous creatinine (product of creatine phosphate metabolism in skeletal muscle–Creatinine is constant amount into plasma in absence of exercise) are freely filtered so they are used to measure _____.
Increase in plasma creatinine indicates a ____ clearance of creatinine from the plasma which indicates decreased GFR resulting from a _____ number of nephrons in acute renal failure.
As kidneys recover from acute renal failure, a ______ in plasma creatine indicates an increase in creatine clearance and an increased GFR.
Increase in plasma creatine may indicate a ______ in GFR due to kidney disease.
Inulin @ 125 ml/min.
Exogenous Inulin (IV fructose polymer) & Endogenous creatinine (product of creatine phosphate metabolism in skeletal muscle–Creatinine is constant amount into plasma in absence of exercise) are freely filtered so they are used to measure GFR.
Increase in plasma creatinine indicates a decreased clearance of creatinine from the plasma which indicates decreased GFR resulting from a decreased number of nephrons in acute renal failure.
As kidneys recover from acute renal failure, a decrease in plasma creatine indicates an increase in creatine clearance and an increased GFR.
Increase in plasma creatine may indicate a decrease in GFR due to kidney disease.
Inulin @ 125 ml/min.
The clearance of any solute, C = ?
If a solute is freely filtered & 50% of the filtered solute was reabsorbed, then the amount of the solute excreted would be ___% of the the amount of the solute filtered. If 99% of the filtered sodium is reabsorbed, then the clearance of sodium would be __ mm/min or less.
C = U x V/Ps
If a solute is freely filtered & 50% of the filtered solute was reabsorbed, then the amount of the solute excreted would be 50% of the the amount of the solute filtered. If 99% of the filtered sodium is reabsorbed, then the clearance of sodium would be 1 mm/min or less.
The clearance of any solute may be more or less than the clearance of inulin. A solute may be only reabsorbed, only secreted or both reabsorbed and secreted, in any given segment or segments of the nephron.
Where both solute reabsorption and secretion occurs, the difference in solute reabsorption and secretion determines either net solute reabsorption or net solute secretion. A solute clearance less than the clearance of inulin indicates the solute is not freely filtered at the glomerulus or, if freely filtered, net solute ____ occurs from the tubular fluid in the nephron. A solute clearance greater than the clearance of inulin indicates net solute ____ into the tubular fluid of the nephron.
A ratio of CS to Cin less than 1 indicates net solute ____
A ratio of CS to Cin greater than 1 indicates net solute _____
The clearance of any solute may be more or less than the clearance of inulin. A solute may be only reabsorbed, only secreted or both reabsorbed and secreted, in any given segment or segments of the nephron.
Where both solute reabsorption and secretion occurs, the difference in solute reabsorption and secretion determines either net solute reabsorption or net solute secretion. A solute clearance less than the clearance of inulin indicates the solute is not freely filtered at the glomerulus or, if freely filtered, net solute reabsorption occurs from the tubular fluid in the nephron. A solute clearance greater than the clearance of inulin indicates net solute secretion into the tubular fluid of the nephron.
A ratio of CS to Cin less than 1 indicates net solute reabsorption
A ratio of CS to Cin greater than 1 indicates net solute secretion
Increase in urinary output of water is only done by _____ because water is _____ added in the nephron. Water is constantly being reabsorbed.
The fracional excretion of water, FeH2O, is the fraction of glomerular filtrate not reabsorbed from the tubualr fluid alond the nephron and therefore, appearing as uring.
FeH2O =
Increase in urinary output of water is only done by reabsorption because water is never added in the nephron. Water is constantly being reabsorbed.
The fracional excretion of water, FeH2O, is the fraction of glomerular filtrate not reabsorbed from the tubualr fluid alond the nephron and therefore, appearing as uring.
FeH2O = V/ C = C x P/ U x V
