Term
| What are the major intracellular, extracellular, and plasma osmotic factors? |
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Definition
1) potassium
2) sodium
3) proteins |
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Term
| What are the primary solutes involved in determining the plasma osmolality? |
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Definition
| 1) Na, Cl, urea, glucose, anions/cations/ plasma proteins (primary osmole) |
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Term
| What are the two methods of assessing osmolality? |
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Definition
1) direct measurement
2) estimate based on sum of major osmoles |
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Term
| How is the osmolality of the plasma estimated with the sum of major osmoles? What is the normal value? |
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Definition
1) P_osm = 2*Na_plasma + [glucose]/18 + [BUN]/2.8 ~= 2*P_Na
2) 280-290mosmol/kg |
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Term
| What is the mechanism for increased Urine osmolality with high P_osm? |
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Definition
| 1) increased ADH secretion results in increased water reabsorption by the kidneys |
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Term
| What ist he lowest urine osmolality possible? highest? |
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Definition
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Term
| Describe how urine is diluted with low ADH |
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Definition
1) PCT - isoosmotic reabsorption
2) loop of henle - hyperosmotic (descending); hypoosmotic (ascending)
3) DCT/collecting duct: no ADH, low water reabsorption, low osmotic gradient |
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Term
| What are the two things required for very concentrated urine? |
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Definition
1) high osmolality in medullary interstitium
2) high permeability to water in distal tubule and collecting duct |
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Term
| Describe coutnercurrent multiplication |
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Definition
1) countercurrent exchanger
2) reduction in solutes at distal aspect
3) water drainage from proximal aspect
4) movement in tubule
5) repeat above steps
**result is high solute concentration in the medullary interstitial fluid** |
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Term
| What percent of hte filtered urea is reabsorbed? |
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Definition
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Term
| Describe the reabsorption of urea and its influence on the osmolality of the medulla |
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Definition
1) waste product of amino acid catabolism
2) concentrated in proximal tubule
3) entry of urea from medulla in descending loop
4) no change in urea concentration in ascending loop
5) ADH - impermeable DCT and cotical collecting duct to urea
6) highly permeable medullary collecting duct |
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Term
| What is the effect of ADH on the distal tubule and collecting duct (cortex and medulla) |
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Definition
1) incrased H2O permeability
2) increased H2O permeability
3) increased H2O, urea permeability |
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Term
| What are properties of the vasa recta that prevent washout of the interstitium solutes? |
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Definition
1) very low rate of blood flow through the vasa recta
2) countercurrent exchange |
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Term
| Equation: osmolar clearance (C_osm) |
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Definition
1) C_osm = U_osm*V/P_osm
2) volume of plasma cleared of all solutes per minute |
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Term
| Equation: free water clearance (C_H2O) |
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Definition
1) C_H2O = V - C_osm = V - (U_osm*V/P_osm)
2) rate at which solute-free water is excreted by the kidney
3) C_H2O > 0 -> water is being excretedin excess of solutes; C_H2O < 0 -> solutes are being excreted in excess of water |
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