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Phys3 RBF & GFR
| Question | Answer |
|---|---|
| Physical solute characteristics of filtrate | 1.Low molecular wgt. 2.small radius. 3.MARCOmolecules w/ Positive charge (due to neg BM & podocytes). 4.Deformable molecules (non-rigid, non-globular). 5.Non protein bound. |
| Net Filtration Pressure (NFP) | NFP=(Pgc-πgc)-(Pbc-πbc). |
| Names for π | 1.oncotic. 2.Collod osmotic. 3.Osmotic |
| Factors that increase the magnitude of the direct determinant: Kf | 1.Inc glomerular surface area (via relaxation of mesangial cells). **Inc GFR |
| Factors that increase the magnitude of the direct determinant: Pgc | 1.Inc renal arterial pressure. 2.Dec Afferent resistance (Afferent VD). 3.Inc Efferent resistance (Efferent VC). **Inc GFR |
| Factors that increase the magnitude of the direct determinant: Pbc | 1.Inc intratubular pressure due to obstruction. **Dec GFR |
| Factors that increase the magnitude of the direct determinant: πgc | 1.Inc systemic-plasma oncotic pressure. 2.Dec renal plasma flow. **Dec GFR |
| What happens to GFR if Pbc or πbc decrease? | INCREASES. |
| What happens to GFR if Kf or Pgc decrease? | DECREASES. |
| How would vasoconstriction of afferent arteriole affect GFR? | Dec Pgc: Dec RBF: Dec GFR. |
| How would vasodilation of efferent arteriole affect GFR? | Dec Pgc: Inc RBF: Dec GFR |
| How would vasoconstriction of both arterioles affect GFR? | Big Dec in RBF, GFR stays the same. |
| As you move down the glomerular capillary from afferent to efferent what happens to the NFP? why? | It decreases b/c the πgc is slowly increasing while Pgc stays relatively the same. **πgc slowly increases b/c fluid is being filtered out of the capillary. |
| Does Pbc change with capillary length? | NO |
| What happens to NFP with LOW glomerular plasma flow? | It decreases rapidly along the length of the capillary due to quickly Inc πgc. Thus Dec GFR **creates wasted capillary. |
| what happens to NFP with HIGH glomerular plasma flow? | πgc doesn't rise as fast so NFP decreases at a very slow rate. this Inc GFR. **Inc delivery of fluid outpacesthe filtration, πgc doesn't rise as fast. |
| At any given length along the capillary, there is a ________ NFP with higher flow rate? | GREATER. **filtration also occurs along a greater length of the capillary. |
| What is the relation b/w GFR and RBF? | DIRECTLY RELATED: Inc RBF -> Inc GFR. Dec RBF -> Dec GFR. |
| Do GFR and RBF increase linearly? | NO, the effect on GFR saturates at high plasma flows. **This occurs at RBF 600ml/min which produces a GFR of 125ml/min. |
| Filtration (FF) represents | the volume of filtrate that forms from a given volume of plasma entering the glomerulus. **Greater at lower flows, less at higher flows. |
| Equation for FF | FF = GFR/RBF |
| Effects of Pgc, RBF, GFR, and FF: Afferent vasoconstriction (Inc resistance) | 1.Pgc:Dec. 2.RBF:Dec. 3.GFR:Dec. 4.FF: |
| Effects of Pgc, RBF, GFR, and FF: Afferent vasodilation (dec resistance) | 1.Pgc:Inc. 2.RBF:Inc. 3.GFR:Inc. 4.FF:Dec. |
| Effects of Pgc, RBF, GFR, and FF: Efferent vasoconstriction (inc resistance) | 1.Pgc:Inc. 2.RBF:Dec. 3.GFR:Inc. 4.FF:Inc. |
| Effects of Pgc, RBF, GFR, and FF: Efferent vasodilation (dec resistance) | 1.Pgc:Dec. 2.RBF:Inc. 3.GFR:Dec. 4.FF:Dec. |
| Can arteriolar resistance changes (VD & VC) lead to changes in flow tha influence GFR independent of effects on Pgc? | YES, they can cause a change in RBF which will affect FF. **FF=GFR/RBF |
| How does the effect of increasing EFFERENT arteriolar resistance change the factors influencing GFR? | 1.Mild/moderate resistance: Pgc dominates which will cause an INCREASE in GFR. 2.Moderate/high resistance: RBF dominates which will cause a DECREASE in GFR (b/c RBF is decreasing) |
| effects of a Nephrectomy on GFR | Decreased afferent arteriolar Resistance causes a large INCREASE in GFR. |
| effects of ACE inhibitors/ANG II blockers on GFR | Decreased efferent arteriolar resistance will DECREASE GFR at the same renal artery pressure below 105mmHg. **could lead to renal failure. ANG II is an important GFR autoregulator. |
| Arteriolar preference of ANG II | EFFERENT arteriole. SNS stimulation with ANG II will cause a VC of both afferent and efferent arterioles, however the effect is greater on the EFFERENT so the Pgc will INCREASE. **keeps a more constant GFR despite RBF decrease. |
| Vasa Recta | Formed from the effernet capillaries from the juxtamedullary nephrons. **they follow the tubules deep down into the medulla. |
| What are the 2 main forces governing the dynamics in the Peritubular capillaries (PTCs) | 1.Starling forces: make the PTCs favor reabsorption b/c π(PTC) is Inc due to fluid filtration and P(PTC) is DEC due to efferent VC. 2.Glomerular Dynamics: determines starling forces. |
| Why is reabsorption favored in the PTCs? | 1.High osmotic pressure π(PTC). 2.Low hydrostatic pressure P(PTC). |
| Reflex response to volume expansion (effects on kidneys) | 1.Dec SNS & RAAS. 2.VD of afferent & efferent. 3.Large Inc in RBF. 4.small Inc in GFR (slight dec due to ANG II & efferent VD). 5.Dec FF. 6.Dec fluid through BC. 7.Inc P(PTC) (due to VD efferent). 8.Dec π(PTC) (due to dec FF & Inc RBF). 9.EXCRETI |
| Reflex response to volume contraction (effects on kidneys) | 1.Inc SNS & RAAS. 2.VC afferent & efferent (more so efferent b/c ANG II). 3.Large Dec RBF. 4.small Dec GFR. 5.Inc FF. 6.Inc fluid through BC. 7.Dec P(PTC) (due to VC of efferent). 8.Inc π(PTC) (due to Inc FF & Dec RBF). 9.REABSORPTION. |
| 2 Autoregulatory prcoesses keeping RBF & GFR from varying too widely (this protects the kidney) | 1.Myogenic response (as BP Inc, so does Resistance & vica versa, this keeps flow the same). 2.Tubuloglomerular feedback (Dec BP Dec GFR & Dec NaCl which causes macula densa to paracrine VD afferent arteriole. Vica versa is true). |
| Renal Autoregulation: Tubuloglomerular feedback: High BP (or pressure in afferent arteriole) | Causes: 1.Inc GFR. 2.Inc NaCl. Macula Densa release paracrine hormones causing: 1.Afferent VC. 2.Dec GFR (via Dec RBF). 3.Dec NaCl |
| Sympathetic effects on RBF and GFR | VC both afferent and efferent arterioles. 1.DEC RBF. 2.slight Dec or relatively constant GFR. **Inc FF. |
| RAAS effects on RBF and GFR | ANG II constricts afferent & efferent arterioles (efferent more so than afferent). 1.Dec RBF. 2.GFR relatively constant (smaller decrease due to Inc Pgc). **Inc FF. |
| ADH effects on RBF and GFR | Total RBF & GFR remain fairly constant despite some VC. |
| ANP effects on RBF and GFR | VD afferents and VC efferents. 1.Inc RBF (VD afferents more than VC efferents). 2.Inc GFR. **Dec FF and inhibits renin secretion. |
| When are protstaglandins helpful in regulating GFR and RBF? | during high SNS and RAAS outflow. It protects against excessive vasoconstriction. |
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WeeG
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