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17 Cards in this Set

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What is the normal range for urine mosm?
75-1200
What is considered to be hyposmotic urine?
urine <300 mosm
What are the 3 things you need to make hyperosmotic urine?
1) corticopapillary gradient
a. countercurrent multiplication
b. urea recycling
2) vasa recta
3) ADH
What are the 2 ADH stimulants?
1) decrease in blood volume
2) deprive of water (increase osmolarity)
What are the 2 ADH inhibitors?
1) alcohol
2) drink a lot of water (decrease osmolarity)
Why do you dilute urine before you concentrate it?
build up concentration gradient so that ADH allows water to move out of the tubular fluid
What determines the maximum possible urine concentration?
the concentration at the tip of the papilla
Does the early distal tubule (the "cortical diluting segment") participate in countercurrent multiplication?
No - because it is not part of the loop of henle (but is does dilute the tubular fluid by absorbing solute thru the Na/Cl- cotransporter
How do loop diuretics cause people to make dilute, less concentrated urine?
inhibit 3-ion transporter, reducing corticopapillary gradient - cannot make concentrated urine
What formss the CP gradient?
1) 60% NaCl
2) 40% urea
How does the vasa recta keep from dissipating the corticopapillary gradient?
1) blood flow is low
2) the vasa recta acts as a countercurrent exchanger
Is countercurrent exchange active or passive?
passive
Is there any depletion of medullary solutes in the vasa recta?
yes, but it is slight (300 mosm at beginning, 325 mosm at end)
What happens if the blood flow in the vasa recta increases too much?
wash out nutrients too fast - cannot equilibrate with surrounding interstitium
What are the ADH receptors called and where are they located?
V2 receptors - basolateral membrane of principal cells
Why does ADH act so quickly?
prepackaged in principal cell and ready to go
What mechanism does ADH work thru?
Gs protein - AC - cAMP - PK - phosphorylation - AQP2 into membrane