Urine Concentration and Dilution Flashcards
What is ADH?
Antidiuretic hormone
- Produced in pituitary gland in response to high osmolarity sensed by osmoreceptors in hypothalamus (triggers release of ADH)
- Affects collecting duct to place aquaporins to increase H2O reabsorption
- brings osmolarity back down to 300 mOsm
Descending loop of henle is a ____ segment
concentrating
Permeable to H2O, impermeable to solutes
Thick asending limb of henle’s loop are _____ segments?
Diluting
Permeable to solutes, impermeable to H2O
Where is the majority of loop of henles?
Juxtamedullary- mainly in medullary interstitium
Cortical nephron (majority)- mainly in cortex
Which nephrons are responsbile for creating concentration gradient?
Juxtamedullary
All collecting ducts run though the _____
medulla
60-70% of filtrate is reabsorbed in the ___ ___.
Proximal tubule
At end of proximal tubule, osm in nephron is ____
300 mOsm (isoosmotic d/t absorption of solute and H2O)
What is osm at bottom of loop of henle?
>300 mOsm. Can be as high as 1200
What is the osm at end of ascending loop of henle?
100-150 d/t dilution from absorption of solutes
What is reabsorbed in distal tubule?
Na, Ca, Cl reabsorbed. K secreted
What is osm at end of distal tubule?
hypoosmotic
What happens in collecting duct without ADH?
Only absorbs solutes. Urine will be hypotonic
What happens in collecting duct with ADH?
Reabsorb H2O via aquaporins
Also absorb solutes
Make hypertonic urine
What affects ADH release?
- OSM
- Decreased BP
- Cold
ADH allows water to leave duct only if the area is ____
concentrated
What is the medullary countercurrent multiplier system?
- What creates osmotic gradient in the loop of henle
- U-shape is essential for its function (creates countercurrent essential to establishing osmotic gradient)
Where does the change in concentration gradient start in the loop of henle?
Starts in ascending loop of henle by Na/Cl/K transporter creating 200mOsm gradient (that transporters Tmax) between ascneding loop of henle and interstitium
What happens after osmotic gradient is created in ascending loop?
The interstitium (which is 200 mOSM higher than ascending limb) equalizes with descening limb (making it 400 mOsM as well)
What are the drivers of the concentration gradient in the loop of henle?
Ascending limb transporters
What is the Tmax of the acending limb transporters (NA/CL/K)
Max 200 mOsm gradient
In loop of henle, the more fluid we move, the more the gradient will
increase
How does collecting duct become hypertonic?
It will equilibrate with whatever the osmolarity is in the interstitium (interstitium is same osm on both sides of ascending loop of henle)
When ADH present, aquaporin channels are placed and water will move to concentration gradient, concentrating urine
Urea contributes to about ___ of th eosmolarity
40%
Urea is _____ and gets ____ in gradient and contributes to gradient.
recycled; stuck
What is the vasa recta?
U-shaped capillaries around loop of henle
Why is the vasa recta u-shaped?
So that nutrients won’t be washed away. Maintains concentration gradient and keeps solutes where they area
Main characteristics of vasa recta?
- preserves concentration gradient created in medulla
- also has countercurrent
- maintains low blood flow so gradient won’t be washed away
The vasa recta is also called the ___ ___ ___
counter current exchanger
What does the concentration of urine depend on?
- Plasma level of ADH
- Osmolar concentration of interstitial fluid surrounding collecting ducts
- urea recycline
- vasa recta
What is the process for making concentrated urine?
Dehydration–> higher plasma osmlarity–> higher ADH levels–> increased AQP channels–> increased water reabsorption–> more concentrated urine
