Urine Concentration

Question 1

GR: The system in loop of Henle/vasa recta is called “counter-current”

Answer 1

Because the flow in its adjacent descending limb and ascending limb is parallel and opposite

Question 2

What is the counter current MULTIPLIER system? Why is it called so? What is its aim? How much is its force?

Answer 2

-Loop of Henle
-Because this flow causes the osmolarity of interstitial space to be multiplied in vertical direction from cortex (300 mOsm/L) to inner medulla, it throws NaCl in interstitial space (Active system)
-Building up osmotic gradient in renal medullary interstitium
-create about 600 mOsm/L of tge interstitial osmolarity

Question 3

GR: Ascending loop of Henle recieves hypertonic fluid

Answer 3

1. Reabsorption of water along descending limb
2. Some urea enters the descending limb

Question 4

What is the counter current EXCHANGER system? Why is it called so? What is its aim?

Answer 4

-Vasa recta
-it exhanges NaCl and urea between its limbs (salts from interstitial space go to the descending limb and gradually it conc inc so in ascending limb it leaves again to interstitium and so on. It is a passive system. It also exchanges water between its limbs which comes out in descending limb to interstitial space then move back to ascending limb to circulation.
-Aim is to maintain the hyperosmolarity gradient in medullary pyramids and prevents NaCl and urea in interstitium from being removed by circulation.

Question 5

Describe mechanism of counter-current exchanger system

Answer 5

1. Keep salts in interstitial space
   a. In the descending limb, the solutes (NaCl and urea) diffuse from medullary interstitium into blood in vasa recta.
   b. In ascending limb, at its beginning the solutes become highly concentrated compared to surrounding zone and diffuse back to interstitium passively
2. Remove water from interstitial space
   Thus water is transported from vasa recta back to circulation. Therefore, solutes recirculate in the medulla and are trapped in the medulla while excess water is removed by vasa recta to general circulation and hyperosmolarity is maintained.

Question 6

What is the source of wtaer removed by vasa recta?

Answer 6

Reabsorption from:
1. Descending limb of LH
2. Descending limb of vasa recta
3. DCT and CD into interstitium

Question 7

What is the site and mechansim of urea trapping by collecting duct? What is its force?

Answer 7

Site: Inner medullary collecting ducts which is highly permeable to urea in presence of ADH
Mech
-The outer cortical portion is permeable to water but not to urea thus urea conc rises
-The inner medullary portion is permeable to both therefore urea moves passively to interstitium
-In the same time the ascending limb of loop of Henle is less permeable to urea so urea is trapped in interstitium.
-This creates 600 mOsm/L

Question 8

What is the effect of high protein diet on urine conc?

Answer 8

Inc protein in diet inc urea production and conc ability of kidney.