Medullary counter-current mechanism Flashcards
What is the concentration of the interstitial fluid in the cortex of the kidney?
300 mOsm/kg
What is the concentration of the interstitial fluid in the deep medulla of the kidney?
1200 mOsm/kg
How does the concentration of the interstitial fluid from the cortex to the deep medulla of the kidney change?
It increases
What is the name of the concentration gradient in the interstitial fluid from the cortex to the medulla?
The corticopapillary gradient
What type of nephron creates the corticopapillary gradient?
Juxtamedullary nephrons
What part of the juxtamedullary nephron creates the corticopapillary gradient?
Loop of Henle
What is the first step in creating the corticopapillary gradient?
Thick ascending limb of loop of Henle
sodium ions and chloride ions move from tubular lumen into interstitial fluid
creates an osmotic gradient of 200 mOsm/kg between the tubular lumen and the interstitial fluid
interstitial fluid has a higher osmolality
What is the second step in creating the corticopapillary gradient? (after thick ascending limb step)
Descending limb of loop of Henle
water molecules move from tubular lumen into interstitial fluid
until osmolality in tubular lumen is same as in interstitial fluid
tubular lumen has a higher osmolality than what it started with
What is the third step in creating the corticopapillary gradient? (after descending limb step which is after ascending limb step)
Fluid in tubular lumen moves round from the descending limb into the ascending limb
What happens after the third step of creating the corticopapillary gradient?
The steps repeat themselves in order
What contributes to the corticopapillary gradient?
Urea
How does urea contribute to the corticopapillary gradient?
Urea transporters on apical domain of epithelial cells in medullary collecting duct
urea moves from the tubular lumen into the interstitial fluid
high concentration of urea in interstitial fluid in deep medulla
What regulates expression of urea transporters on the apical domain of epithelial cells in the medullary collecting duct? How?
ADH
increases expression
What happens to urea in the interstitial fluid of the deep medulla?
A small portion of it diffuses back into the loop of Henle
What happens to the urea that has diffused back into the loop of Henle from the interstitial fluid in the deep medulla?
It moves with the tubular fluid up the ascending limb of the loop of Henle
into the distal convoluted tubule
into the collecting duct
What is the effect of the recirculation of the urea on the corticopapillary gradient? How?
Increases the concentration of urea in the interstitial fluid in the deep medulla
because only a small portion of it diffuses back into the loop of Henle each time, so most it remains there and accumulates there
contributing to corticopapillary gradient
What maintains the corticopapillary gradient?
Vasa recta
How does blood flow through the vasa recta?
Down the descending limb of the vasa recta
then up the ascending limb of the vasa recta
How does blood flow through the vasa recta compare to the flow of tubular fluid in the loop of Henle?
Blood flow down descending limb of vasa recta is ajdacent to tubular fluid flow up the ascending limb of the loop of Henle
Blood flow up ascending limb of vasa recta is adjacent to tubular flud flow down descending limb of loop of Henle
What happens to the blood in the descending limb of the vasa recta?
Sodium chloride from interstitial fluid diffuses into it
also it loses water
becomes more concentrated
has a higher osmolality
What happens to the blood in the ascending limb of the vasa recta?
Water moves from descending limb of loop of Henle and descending limb of vasa recta move into it
becomes more dilute
has a lower osmolality
How does the concentration gradient of the vasa recta compare to the corticopapillary gradient?
They’re the same
How do the vasa recta maintain the corticopapillary gradient?
Water moves from descending limb of loop of Henle and descending limb of vasa recta into ascending limb of vasa recta
doesn’t dilute the corticopapillary gradient
What is the relative blood flow through the vasa recta? Why?
Slow
To supply metabolic needs of cells
to give time for water to move into it
What is the purpose of the corticopapillary gradient?
Allows for water reabsorption in the collecting duct
through the aquaporin channels
from the tubular lumen into the interstitial fluid
