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25 Cards in this Set

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What is responsible for making the osmotic gradient in the medullary interstitum
NaCl reabsorption from the ascending loop of henle
3. Interstitum becomes progressively more concentrated as you move to the medulla. What is the final concentration
1200 mOs
What does countercurrent allow?
Allows you to be increasingly osmotic as you move down the tube
8. What happens when someone has been on a restricted water intake?
1. They secrete ADH
2. Water flows out of collecting tubules
3. Urine becomes concentrated
4. Increased urea permeability
9. What happens to the college student who is victim of water loading?
1. Low levels of ADH
2. Low H2O permeability in CT on down
3. Excrete a dilute urine
4. Low urea permeability
10. What happens if the pt is on loop diuretics (which inhibit the NKCC transporter in thick ascending limb)
1. Urine doenst get diluted in TAL
2. Interstitium does not get concentrated
3. Increase delivery of Na and solutes to distal nephron (osmotic agents that prevent H20 reabsorption)
4. Decreased H2O reabsorption in the descending limb
5. SO
1. You block the ability to form concentrated OR dilute urine
1. Can’t make
1. Concentrated during hydropenia
2. Dilute during water loading
12. why will Urea give about half of the osmoles in the increasing osmolality of the interstitum
1. Helps give gradient to move NaCl from inside the lumen to out
1. Effects passive transport
Low protein intake- if there is a reduced metabolic production of urea, what effect wil occur?
compromised ability to create concentrated urine.
Dehydration: ADH levels are high. What effect does this have on the medullary interstitium?
This leads to increased urea permeability, leading to a more concentrated medullary interstitum. Urine will be more dilute.
Describe GFR and ADH in overhydration.
GFR is high, ADH levels are low.
Using a loop diuretic accomplishes what?
Causes the urine to become isosmotic because you block the NKCC channel. NaCl stays in the lumen at TAL, increasing urine volume.
Summarize the osmotic gradient generation.
1. Salt without H2O deposited in the interstitum from TAL.
2. Salt accumulates via countercurrent exchange of the ascending/descending vasa recta.
3. Addition of urea
What is countercurrent exchange?
Water flows out and solute flows in descending LOH.
This leads to an increased solute concentration at the loop, which draws H2O toward it.
The water flow pushes into the thin and thick ascending limbs, which dilutes the solute.
Solute also flows out in the ascending limbs.
NET EFFECT: BLOOD EXITING MEDULLA IS LESS HYPERTONIC THAN THE BLOOD IN THE CORTEX, SO THE OSMOSTIC GRADIENT IS PRESERVED
What is teh key concept of countercurrent multiplication?
1. Concentrates loop fluid and then re-dilutes it.
2. This process presents a dilute urine to the distal tubule.
3. Also produces a cencentrated medullary interstitum through which the collecting ducts run (the final point of concentration/dilution).
Name the ways Na+ passes out of the TAL (3).
Through:
1) paracellular
2) Na+/H+ transporter
3) Na/K/2C triporter
What is the max concentration of excreted urine?
1200 mOsm
What happens when someone is on a restricted water diet?
They need an anti-diuresis treatment as well.
Anatomically, where does ADH act on?
From the initial collecting tubule to the inner medullary collecting duct.
What happens to the osmolality as you descend into the medulla?
It becomes increasingly HYPEROSMOTIC
Does urine get diluted in the TAL?
YES! NaCl can vamoose, but H2O cannot follow.
What are the two solutes that contribute to the increasing osmolality of the medulla?
NaCl and urea.
Is urea freely filtered?
YES
What stimulates the urea transporters in the inner medulla?
ADH
What affect does low urine flow have on urea reabsorption?
Low urine flow allows more time for reabsorption to occur, increasing the level or reabsorption.
What moves into the vasa recta via active transport?
NOTHING!!! Passive and facilitative diffusion can occur no problem, tho.