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Phys3 Con/dilut urin
Phys3 Concentration & dilution of urine
| Question | Answer |
|---|---|
| Functions of countercurrent multiplication | 1.Concentrates loop fluid and then re-dilutes that fluid. 2.Presents dilute urine to the distal tubule. 3.Creates concentrated medullary interstitium where the collecting ducts run. |
| Where is the point of final concentration or dilution? | Collecting ducts |
| When is medullary interstial osmolality the highest? | During periods of dehydration or water deprivation. **it is halved during periods of excess hydration. |
| What would happen if the transport in the thick ascending limb is inhibited? | The lumen would not become diluted and the interstitium would not become concentrated. |
| Why does the interstium become so concentrated in the medulla? | B/c the vasculature isn't as abundent so the solutes reabsorbed remain in the interstium instead of being taken up into the PTCs like in the cortex. |
| 1st step of the countercurrent multiplacation? | Called the Initial process, produces a "single effect". **Na & Cl are reabsorbed from the ascending loop which creates a hyperosmotic interstium. |
| How is the "Single effect" accomplished differently in the thin Vs. thick ascending loop? | 1.Thin: passive movement of NaCl. 2.Thick: passive & active movement of NaCl. |
| What is the osmolality gradient b/w the Ascending lumen and the interstium? | 200mOsm. |
| What is countercurrent exchange? | The process of crossing b/w ascending and descending vessels of the looped vasa recta that maintains the osmotic gradient in the medulla. **a straight capillary would become hyperosmotic and cause a washout of medullary interstitial solutes. |
| How does the osmolality of the interstium change from outer to inner medulla? | It becomes progressively more hyperosmotic. **Max of 1200 mOsm at papilla. |
| What happens to urine during water restriction with high levels of ADH | Becomes more concentrated b/c water flows out of the collecting tubules. **Increased urea permeability adds to this effect. |
| How does the osmolality of the cortical interstitium compare to that of the plasma? | They are the same due to the heavey vasculature. |
| What all does ADH affect in the IMCD (Inner medullary Collecting Duct) | 1.Water reabsorption. 2.Urea reabsorption. |
| What occurs at the Collecting tubules/ducts during water overload? | 1.Low ADH levels. 2.Low H2O permeability. 3.Low Urea permeability. 4.Excrete a DILUTE urine. |
| What are loop diuretics and what occurs within a patient that is taking them? | They inhibit the Na/2Cl/K transporter in the thick ascneding loop: 1.Urine doesn't get diluted. 2.Interstitium doesn't get concentrated. 3.Na in urine prevents H2O reabsorption in the Collecting Ducts. |
| Affect of loop diuretics on urine concentration? | 1.Inhibits urine concentration during hyrdopenia. 2.Inhibits urine dilution during water loading. **Urine is Isosmotic with plasma. |
| Interpreting Free water clearance C(H2O). | C(H2O) = V - C(osm). ** + if urine is LESS concentrated than plasma. **- if urine is MORE concentrated than plasma. **0 if urine & plasma are isosmotic. |
| How does the urea concentration changes as you descend down the medulla? | [Urea] rises steeply from middle of outer medulla to the papilla. **since H2O is reabsorbed luminal [urea] is 50X plasma [urea] in the MCD (medullary collecting duct). |
| What happens to urea in the IMCD? | Some is reabsorbed, but due to low BF, urea stays in interstium to increase medullary osmolality. |
| Key contributers to medullary osmolality | 1.50% urea. 2.50% NaCl. |
| Flows affect on urea reabsorption | 1.Low flow: more H2O gets reabsorbed & therefore more urea gets reabsorbed. 2.High Flows:less water is reabsorbed & therefore less urea reabsorbed. **Dependent on concentration gradient created by water movement. |
| Is urea excretion Inc or Dec with a High Flow? | INCREASED. |
| Affect on Urea: renal disease | 1.Dec GFR. 2.Dec flow. 3.Inc H2O & Urea reabsorption. 4.INC BUN. |
| Affect on Urea: low protein intake | 1.Dec urea production. 2.Dec ability to concentrate urine. |
| Affect on Urea: dehydration | 1.Dec GFR. 2.Inc ADH. 3.Inc H20 & Urea reabsorption. 4.Inc medullary [urea]. |
| Affect on Urea: overhydration | 1.Inc GFR. 2.Dec ADH. 3.Dec H2O & urea reabsorption. 4.High vol of dilute urine |
| is there active transport involved in the vasa recta's countercurrent exchange? | NO |
Created by:
WeeG
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