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Phys3 Con/dilut urin

Phys3 Concentration & dilution of urine

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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