Lecture 4 — Countercurrent Multiplicstion And Urea Recycling Flashcards
What are the 2 types of nephron?
Cortical nephron
Juxtamedullary nephron
How do the lengths of loop of Henles compare in cortical and juxtamedullary nephrons?
Cortical = short LoH
Juxtamedullary = Long LoH
What are the capillaries around the LoH called?
Vesa recta
What are the 2 mechanisms which establish a Corticopapillary gradient?
Countercurrent multiplication
Urea recycling
What transporter is important in establishing a corticopapillary gradient around the nephron?
NKCC transporter
If a solution has a high Osmolality what does this mean?
Low amount of water high amount of solute
What is the rough osmolality of the fluid at the start of the LoH and the surrounding interstitium?
300miliosmoles
How does the osmolality of the fluid in the LoH change as you descend the loop?
What rough value does it reach?
Increasing osmolality
(Gets more and more concentrated)
Reaches around 1200 miliosmoles
Which part of the LoH is permeable to water?
Descending limb
Water leaves descending limb into Vesa recta
What is meant by the counter current flow in the Loop of Henle?
Fluid flows through loop one direction and blood flow through Vesa recta flows in the other
Describe how the osmolality changes as you travel through the loop of Henle:
As water moves out of the descending limb into the vesa recta the Osmolality in the LOH increases from 300 to 1200
As you travel up the ascending limb NKCC transporters pump ions out of the LOH into the medullary space decreasing osmolality to about 100
How does the osmolality of the vesa recta change as it flows past the ascending limb to the descending limb?
Why?
Solutes pumped out of the ascending limb by the NKCC transporters reabsorbed back into blood making it more concentrated (higher osmolality 1200)
As it flows past the descending limb more and more water moves in so the osmolality decreases since it becomes less and less concentrated
Why is a high concentration of solutes in the medulla/high osmolality of the medulla important for the collecting duct?
Means more water moves out of the collecting duct into the interstitial space to be reabsorbed via vesa recta
What hormone needs to be present in order for the water to move down the osmotic gradient from the collecting duct?
ADH
Water flows through the aquaporins to the interstitium then the vasa recta
What word can describe the fluid in the LOH at the end of the ascending limb compared to the interstitium ?
Hypoosmotic
In the thick ascending limb what is the difference in Osmolality that’s maintained between the tubular fluid and interstitium?
200 milli osmoles
What allows for countercurrent multiplication to maintain a corticopapillary gradient?
Descending limb where water is lost but Na+, Cl- and Urea absorbed
Ascending limb, where solutes lost
Slow flow
Water absorbed from the CD in presence of ADH into vasa recta maintaining high osmolality of interstitium
How is urea used to help reabsorb water?
More urea in interstitium leads to more water getting drawn out of nephron to be reabsorbed
How much of the urea in the glomerulus filters into the Bowmanns capsule?
100%
It’s freely filtered
How much urea gets reabsorbed in the PCT?
50%
How does Urea move in the descending limb of the LOH?
Lots of urea moves into the descending limb
How does urea move in the ascending limb?
It’s impermeable to urea so the high conc of urea remains in the LOH
How does urea move in the collecting duct?
Urea moves out of CD into interstitium across Urea Transporters (UT1)
What hormone increases the expression of Urea Transporters (UT1) in the collecting duct making more urea be reabsorbed into the interstitium then blood?
ADH
How much urea gets reabsorbed?
How much stays in the COllecting duct?
Reabsorbed = 70%
Stays in CD = 40%
How does urea recycling help with water reabsorption?
Leads to urea leaving the CD across Urea transporters (UT1)
Urea in interstitium draws water out of collecting ducts
Inc ADH = inc UT1
