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Medullary concentration gradient


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Why is it important to concentrate your urine?
How much can you conc. it?
-To conserve body water.
-Conc up to 1200 mOsm, the same as the ISF of inner medulla.
Where is ADH action important (in what renal cells)?
In the collecting duct cells.
How does ADH work?
1. It's carried in the blood.
2. Released, binds membrane receptor on coll. duct cell.
3. Activates cAMP-depend. PKA, which causes aquaporin II to
insert on lumenal membrane.
what is the min and max concentration that the filtrate can be?
50 Osm is minumum
1200 Osm is maximum.
what is the purpose of countercurrent multiplication?
to develop a concentrated ISF in the inner medulla, to allow H2o reabsorption from the medullary collecting duct.
What ions move from which parts of the nephron, in order to develop the high ISF concentration?
-Water reabsptn from desc limb.
-Na/Cl reabsptn from ascnd limb.
-Water NOT reabsbd from asc. lmb
What is countercurrent exchange, and what is its purpose?
-Exchange of H2O/Na/CL from peritubular capillaries. -Prevents washout of concentrated ISF develpd by countercurr. multiplication.
What are the special peritub. capillaries called?
Vasa recta, in inner medulla.
How do H2O/Cl/Na move when flowing through vasa recta by the descending limb?
H2O moves out, Cl/Na move in, so the blood is 1200 mOsm at the bottom of the loop.
How do H2O/Cl/Na move when flowing through vasa recta by the ascending limb?
H2O moves back in, Cl/Na move out, so the blood is once again 300 mOsm (normal) at the top.
If there was no Vasa recta, what would happen?
All of the Na/Cl creating the concentrated ISF would move down their gradient into blood vessels, and washout the ISF.
what is urea's role in concentrating urine?
As Na/Cl are reabsorbed from asc. limb, urea replaces them. This makes NaCl reabsptn more efficient. Urea is then reabsorbed at collecting duct.

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