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18 Cards in this Set
- Front
- Back
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Medulla is separated into clusters of _________.
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Medullary Rays
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The majority of blood flow in the kidneys goes to the ______.
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Majority of blood flow goes to cortex
Medulla is relatively ischemic; kidneys are super sensitive to ischemic insult |
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Cortical vs Juxtomedullary Nephrons
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Cortical nephrons: superficial, don't penetrate medulla
Juxtomedullary: plunge deeply into medulla from cortex; establish hypertonic gradient in medulla |
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Which Starling forces favor renal filtration? Oppose?
What is the formula for the glomerular filtration rate of a single nephron? |
Starling forces favoring filtration:
Glomerular Capillary Hydrostatic Pressure (Pgc) Oncotic Pressure in Bowman's Space (Pibs) Oppose Filtration: Bowman's space HYDROSTATIC pressure (Pt) Colloid (oncotic) capillary pressure (Pigc) Note: Pibs (BS oncotic pressure is negligible) SNGFR = Kf(deltaP-Pigc) Where Kf = constant of porosity deltaP = Transglomerular capillary pressure gradient = Pgc - Pbs Pigc= Glomerular capillary colloid Osmotic pressure |
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Glomerular Capillary vs Peritubular Capillary:
Forces Favoring Filtration/Reabsorption |
Glomerular: Filtration (bc Hydrostatic P > Osmotic P)
Peritubular: Reabsorption (bc Osmotic pressure > Hydrostatic) |
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Equation for filtration fraction.
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GFR/Renal Plasma Flow
Should be about 0.20 |
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What is the effect of a decreased renal plasma flow with a constant glomerular filtration rate?
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Filtration Fraction: GFR/Renal Plasma Flow
Note: Filtration Fraction increases! When decreases plasma flow, downstream effect is increase in peritubular colloid osmotic pressure (favors reuptake of sodium/water) |
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78-year old man with prior history CAD, presents with dyspnea, and heart failure.
PE shows BP 90/40, diffuse edema. What would you expect to GFR, RPF, and urinary sodium to be (generally)? Why? |
GFR: Moderately Low
RPF: Low Urinary Sodium: Low GFR is preserved while RPF is low in heart failure (via autoregulation); thus colloid osmotic pressure (Pigc) rises in terminal glomerular capillaries and downstream PERITUBULAR (!) capillaries, and allow uptake of sodium + H2O. |
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What is the autoregulatory response to renal hypoperfusion?
Causes of hypoperfusion? |
Causes of renal hypoperfusion:
Hypovolemia, bilateral renal artery stenosis, severe CHF Autoregulation of GFR: Inc Renin-AgII-->Efferent arteriole constriction Inc NO, Inc PGs-->Afferent arteriole dilation Both allow for maintenance of GFR |
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What is the renal effect of ACE-inhibitor use on a patient with CHF?
What other drug could mimic this effect? |
No Renin-AgII effect to maintain GFR; thus diminished GFR
NSAIDs could block PG synthesis and prevent GFR maintenance |
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How do size, charge, and shape affect glomerular filtration?
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Size (glomerular BM)
Charge (negative charge-->less passage; GBM is negatively charged) Shape (slit diaphragm; GBM) Water and small molecules easily pass! Proteins, like albumin, do not pass. Note: Filtration goes from inside capillary to layers of glomerulus to bowman's space to tubule |
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How would a defect in nephrin contribute to proteinuria?
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Between each podocyte (foot process) in glomerulus is a slit diaphragm.
Slit diaphragm consists of nephrin. If lack nephrin, slit diaphragm becomes permeable by proteins. |
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Formula for clearance of substance x.
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Cx = Ux x V ÷ Px,
where Cx is the clearance of substance “x” Ux is the urinary concentration of substance “x” V is the urinary flow and, Px is the plasma concentration of substance “x” |
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Would you expect creatinine clearance to over- or under-estimate GFR? Why?
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Over-estimate GFR because unlike inuline, creatinine is an endogenous substance and a small proportion is secreted by tubules.
Also, creatinine is related to muscle mass. Serum creatinine tends to be lower on average in women than in men (have less muscle mass than adults). |
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When clearance of inulin exceeds clearance of substance x, then there is net _______ of substance x.
What could you use as substance x? |
Reabsorption
Glucose (glucose should be reabsorbed) (GFR x Plasma glucose) - Glucose excretion = Reabsorption Rate |
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When clearance of substance x exceeds clearance of inulin, then there is net _______ of substance x.
What could you use as substance x? |
Net secretion of substance x
Excretion rate - Filtered Load = secretion rate Could use PAH (a substance that is secreted) |
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Which of the following individuals has a normal GFR?
An 80 year-old woman with a serum creatinine of 1.2 mg/dl A 6 month-old girl with a serum creatinine of 1.2 mg/dl A 7 year-old boy with a serum creatinine of 1.2 mg/dl A 76 year-old man with a serum creatinine of 1.2 mg/dl A 30 year-old male weight lifter with a serum creatinine of 1.4 mg/dl |
The weight lifter has the greatest muscle mass and therefore is likely to synthesize the most creatinine.
Hence, serum creatinine of 1.4 represents a normal GFR. |
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Assume a subject with the following values:
urine flow rate 1 mL/min plasma concentration of inulin 100 mg/mL urine concentration of inulin 12 gm/mL renal artery concentration of PAH 1.2 mg/mL renal vein concentration of PAH 0.1 mg/mL urine concentration of PAH 650 mg/mL plasma concentration of A 10 mg/mL urine concentration of A 2 gm/mL hematocrit 45% 1) What is GFR? 2) What is the effective renal plasma flow rate? 3) What is the renal blood flow? 4) Assuming that substance A is freely filtered, what is the filtered load of substance A? |
1) GFR:
Cin = Uin x V ÷ Pin = 12,000 mg/ml x 1 ml/min ÷ 100 mg/min = 120 ml/min 2) RPF = UPAH x V ÷ PPAH = CPAH = 650 mg/ml x 1 ml/min ÷ 1.2 mg/ml = 542 ml min (True RPF is 10% higher or 596 ml/min) 3) RBF = RPF ÷ (1-Hct) RBF = 596 ÷ (0.55) RBF = 1084 ml/min 4)CA = UA x V ÷ PA CA = 2000 mg/ml x 1 ml/min ÷ 10 mg/ml CA = 200 ml/min Since CA>Cin, there is net secretion |
