Loop of Henle Flashcards
If drugs are nonpolar and high lipid soluble, when water is absorbed in the renal system leaving high concentrations of these substances to be reabsorbed, what stops drugs and pollutants being reabsorbed?
The liver metabolizes them to polar compounds - meaning they get excreted
The fluid that leaves the proximal tubule is…
Isosmotic with plasma (meaning 300 mOmoles/L)
How is fluid leaving the proximal tubule isosmotic?
All the solute movements are accompanied by equivalent H2O movements, so that osmotic equilibrium is maintained.
Do all of the nephrons have their proximal and distal tubules in the cortex?
Yes
Do all nephrons have common or different process for reabsorption and secretion ?
Common
Where does the “very special system” essential for water balance occur? What does it do?
Loops of Henle of juxtamedullary nephrons
Allows the kidneys to create concentrated urine in times of water deficit
What is the max conc. of urine that can be made by human kidneys?
1200-1400 mOsmoles/L
4x more conc. than plasma
What does all the waste products that must be secreted each day amount to in mOsmoles? How much water is lost for this to happen?
600 mOsmoles requiring a minimum obligatory H2O loss of 500 mls
Does this minimum of 500mls of water always get excreted?
As long as the kidney’s are functioning yes.
It won’t even stop if there is no water intake meaning you will keep losing water
What happens if there is excess water intake?
Water is excreted in excess of solute
What is the minimum urine concentration of water in man?
30-50 mOsmoles/L
How are kidneys able to produce urine of varying concentrations?
Loops of Henle of juxtamedullary nephrons act as counter-current multipliers
What does counter current mean in the context of the loop of henle?
Fluid flows down the descending limb and up the ascending limb
What critical characteristics of the loops of henle make them countercurrent MULTIPLIERS?
Ascending limb actively co-transports Na and Cl ions out of the tubule into the interstitium and is impermeable to H2O
The descending limb is freely permeable to H2O but doesn’t pump out Na or Cl
Explain how this system works.
As NaCl is pumped out of the ascending limb, the concentration inside the lumen falls and in the interstitium is rises. This occurs until a gradient of 200 mOsm is established
This increased concentration/osmolarity in the interstitium means that when fluid comes down the descending limb, water leaves the lumen and enters the interstitium which concentrates the fluid inside the descending limb. The interstitium concentration is unaffected by the increase in water from descending limb
Why does water from the descending limb not affect the conc. of the interstitium?
It doesn’t stay there, is reabsorbed by the high osmotic pressure and tissue pressure into the vasa recta
Continue explaining the system.
So since fluid is actually moving down the descending and up ascending limbs, this means that at the bottom of the ascending limb you get very highly concentrated solution that has just left the descending limb.
In order to keep the 200 mOsmol’s conc. gradient with the interstitium, the interstitium near the bottom is much more concentrated than near the top where the ascending limb fluid is less concentrated
From top to bottom, what is the vertical gradient of the interstitium?
300-1200 mOsmol
If the pumping on NaCl from the ascending limb is abolished, what would happen? how can this happen?
All concentration differences are lost and the kidney can only produce isotonic urine
Diuretic frusemide
So in the end, what has the countercurrent multiplier achieved?
- Concentrates fluid on the way down and promptly re-dilutes it on the way back up by removing NaCl.
- One consequence of this is that 15-20% of the initial filtrate (up to 36 l) is removed from the loop of Henle
- Fluid which enters the distal tubule is more dilute than plasma and is hypotonic.
Most important effect is the creation of an increasingly concentrated gradient in the interstitium.
If fluid enters the loop of Henle at 300 mOsm, what level does it leave at?
100 mOsm
What is the vasa recta? How are they important?
A specialized arrangement of the peritubular capillaries of the juxtamedullary nephrons that supply O2 to the medullary WITHOUT disrupting the interstitial gradient set up by loops of henle
How does the vasa recta not destroy the gradient?
The blood flow in the vasa recta is sluggish, allowing time for the plasma in the vasa recta to equilibrate with the surrounding interstitial fluid. The osmolarity of the plasma inside the vasa recta increases as it descends into the medulla, and then decreases again on the ascending side.
This allows blood to flow to the medulla, without eliminating the osmotic gradient.
So what is the point of setting up this interstitial gradient?
When water exits the loop of henle, it enters the collecting ducts.
If the body needs to conserve water, ADH is released into the collecting ducts and binds to aquaporins opening water channels into the interstitium
Since the interstitium is now salty due to the gradient, water can flow freely out and get reabsorbed and the urine gets more concentrated the further down the gradient it does
If water does not need to be conserved the aquaporins simply stay shut
If any of this remains confusing, youtube is a great source and re-read the lecture again!
Will do
