Loop of henle Flashcards
What state does urine enter loop of henle?
Isotonic
Function of loop of henle? (3)
1) Na+ reabsorption
2) Urinary dilution
3) Generate medullary hyperosmoticity- allow water diffuse in descending and collecting duct
What does descending loop do?
Water permeable
Impermeable solutes
What does ascending loop do?
Water impermeable
Permeable solutes
Where is water absorbed in loop of henle?
Descending limb
Where are solutes absorbed in loop of henle?
Ascending limb
Function of descending limb (explain conc change)?
1) Descending limb permeable to water
2) Water flows out due to osmotic pressure
3) Fluid moves down loop it gets more concentrated
Why does water flow out of descending limb?
Due osmotic pressure
Does fluid become more or less concentrated as goes down descending?
More
Lose water
Does fluid become more or less concentrated as goes down descending?
More
Lose water
Explain what occurs in thick ascending limb?
1) Na+ reabsorbed (move out) by Na/K ATPase in basolateral membranes
2) Allows further uptake Na+ by NKCC2
Use gradient (secondary active transport) and pump Na+ out of
tubule lumen
K+ recycled on apical membrane back through lumen (ROMK
channels)
3) Cl- leaves cells through CLCK A channels on basolateral
membrane
4) Negatively charged lumen created- repels Ca2+ etc as move
paracellularly
5) Hyperosmotic interstitium created- aid water uptake
What is function thin ascending limb?
Salt pumped passively
What are 2 ways which Na+ taken up in ascending limb?
1) Na/K ATPase in basolateral membranes
2) NKCC2 uses the gradient (secondary active transport)
Pumps Na+ out lumen of tubule
What is process that NKCC2 pump use?
Secondary active transport
How is K+ recycled?
Where?
Apical membrane
ROMK channels
How does Cl- leave cell?
CLK channels on basolateral membranes
Is the tubule positive or negative charged?
Negative charged- repel Ca2+ and Na+
What does counter current system result in?
Hyperosmotic interstitium
Low water concentration
In ascending limb does tubule become hypo or hyper osmotic?
Hyposmotic
What system is used in outermedulla to ensure water and solute reabsorption?
Counter-current system
What is function of urea? (explain)
Important inner medulla
1) Vasopressin makes collecting duct permeable to urea
2) Urea moves out of collecting tubule into interstitium
3) Urea is osmotically active and trapped in the interstitium
4) Water drawn down conc. gradient to low water conc (gen by urea)
5) Aids urine concentration in the loop of Henle
6) Urea reabsorbed, secreted into tubule and reabsorbed again
7) Urea freely filtered in the glomerulus- 50% of filtered urea is reabsorbed in proximal tubule, remaining 50% enters the loop of Henle
Main function urea?
Create low water conc in intersitium- draws out water
What blood supply to glomerulus?
Vasa recta
Function of vasa recta?
Ensure counter current gradient maintained
Supply O2 to deep structures
Explain how the vasa recta works?
1) Blood moves down descending vasa recta - low solute conc
Solutes move into blood (Na+), water out
Blood more conc
Blood high oncotic pressure- proteins not filtered
By bottom has high solute conc
2) Ascending limb vasa recta water moves from high to low conc
Water moves into vasa recta and is removed
Solutes secreted
Why is vasa recta a loop?
Minimise loss of solute by diffusion- maintain gradient
Why is vasa recta hairpin?
Slow rate blood flow- maintain osmotic grad required water reabsorption
What process do solutes and water move into vasa recta?
Passive diffusion
What does countercurrent system maintian?
Conc gradient
What maintains counter current system?
Selective permeability in the loops of Henle
Passive diffusion in the vasa recta
