Urine Concentration and Dilution

Question 1

What is ADH?

Answer 1

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

Question 2

Descending loop of henle is a ____ segment

Answer 2

concentrating

Permeable to H2O, impermeable to solutes

Question 3

Thick asending limb of henle’s loop are _____ segments?

Answer 3

Diluting

Permeable to solutes, impermeable to H2O

Question 4

Where is the majority of loop of henles?

Answer 4

Juxtamedullary- mainly in medullary interstitium

Cortical nephron (majority)- mainly in cortex

Question 5

Which nephrons are responsbile for creating concentration gradient?

Answer 5

Juxtamedullary

Question 6

All collecting ducts run though the _____

Answer 6

medulla

Question 7

60-70% of filtrate is reabsorbed in the ___ ___.

Answer 7

Proximal tubule

Question 8

At end of proximal tubule, osm in nephron is ____

Answer 8

300 mOsm (isoosmotic d/t absorption of solute and H2O)

Question 9

What is osm at bottom of loop of henle?

Answer 9

>300 mOsm. Can be as high as 1200

Question 10

What is the osm at end of ascending loop of henle?

Answer 10

100-150 d/t dilution from absorption of solutes

Question 11

What is reabsorbed in distal tubule?

Answer 11

Na, Ca, Cl reabsorbed. K secreted

Question 12

What is osm at end of distal tubule?

Answer 12

hypoosmotic

Question 13

What happens in collecting duct without ADH?

Answer 13

Only absorbs solutes. Urine will be hypotonic

Question 14

What happens in collecting duct with ADH?

Answer 14

Reabsorb H2O via aquaporins

Also absorb solutes

Make hypertonic urine

Question 15

What affects ADH release?

Answer 15

• OSM
• Decreased BP
• Cold

Question 16

ADH allows water to leave duct only if the area is ____

Answer 16

concentrated

Question 17

What is the medullary countercurrent multiplier system?

Answer 17

• What creates osmotic gradient in the loop of henle
• U-shape is essential for its function (creates countercurrent essential to establishing osmotic gradient)

Question 18

Where does the change in concentration gradient start in the loop of henle?

Answer 18

Starts in ascending loop of henle by Na/Cl/K transporter creating 200mOsm gradient (that transporters Tmax) between ascneding loop of henle and interstitium

Question 19

What happens after osmotic gradient is created in ascending loop?

Answer 19

The interstitium (which is 200 mOSM higher than ascending limb) equalizes with descening limb (making it 400 mOsM as well)

Question 20

What are the drivers of the concentration gradient in the loop of henle?

Answer 20

Ascending limb transporters

Question 21

What is the Tmax of the acending limb transporters (NA/CL/K)

Answer 21

Max 200 mOsm gradient

Question 22

In loop of henle, the more fluid we move, the more the gradient will

Answer 22

increase

Question 24

How does collecting duct become hypertonic?

Answer 24

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

Question 25

Urea contributes to about ___ of th eosmolarity

Answer 25

40%

Question 26

Urea is _____ and gets ____ in gradient and contributes to gradient.

Answer 26

recycled; stuck

Question 27

What is the vasa recta?

Answer 27

U-shaped capillaries around loop of henle

Question 28

Why is the vasa recta u-shaped?

Answer 28

So that nutrients won’t be washed away. Maintains concentration gradient and keeps solutes where they area

Question 29

Main characteristics of vasa recta?

Answer 29

• preserves concentration gradient created in medulla
• also has countercurrent
• maintains low blood flow so gradient won’t be washed away

Question 30

The vasa recta is also called the ___ ___ ___

Answer 30

counter current exchanger

Question 31

What does the concentration of urine depend on?

Answer 31

• Plasma level of ADH
• Osmolar concentration of interstitial fluid surrounding collecting ducts
• urea recycline
• vasa recta

Question 32

What is the process for making concentrated urine?

Answer 32

Dehydration–> higher plasma osmlarity–> higher ADH levels–> increased AQP channels–> increased water reabsorption–> more concentrated urine