Loop of Henle Flashcards
What is the function of the proximal tubule?
Reabsorption
65-75% NaCl
H2O
Nutritionally Important substances
How much albumin is secreted a day? What happens to it?
30g/0.5%
Completely reabsorbed
How are lipid soluble pollutants removed from the system?
Liver metabolises them into polar compounds - reduces permeability
What is the normal osmolarity of fluid leaving the proximal tubule?
Isosmotic - 300mOmoles/l
Why is fluid leaving the proximal tubule isosmotic?
Solute movements are accompanied by H2O movements
The proximal and distal tubules sit where?
The cortex
What is the maximum concentration of urine that can be produced by the human kidney?
1200-1400mOsmoles/l
Why does the human kidney have a minimum obligatory H2O loss? What is it?
500mls
Because there are waste products amounting to 600mOsmoles which must be excreted
What is the minimum [urine] in a human?
30-50mOsmoles
The loops of Henle act as what?
Counter-current multipliers
What is meant by counter current?
Fluid flows down descending limb, up ascending limb
What is meant by a (counter-current) multiplier?
Ascending limb actively contransports NaCl out, whilst impermeable to H2O
Descending limb freely permeable to H2O, impermeable to NaCl
What is the limiting gradient osmolarity in the ascending limb of the loop of Henle?
200mOsm
What is the net effect of removing NaCl from the ascending limb into the interstitium?
Osmolarity of the lumen decreases
Osmolarity of the interstitium increases
The increased osmolarity in the interstitium next to the ascending limb causes what?
H2O outflow from ascending limb to counteract osmolarity
Why does H2O outflow from the descending limb not cause isosmolarity in the adjacent interstitium?
This water is reabsorbed by the high oncotic and tissue pressure into the vasa recta
Greater concentration of the descending limb causes what?
Greater concentration of the interstitium by adding salt from ascending limb
What is the vertical gradient of the interstitum?
300–>1200 mOsmol
How do Loop diuretics effect diuresis?
Block active transport of NaCl out of ascending limb - no conc differences - no gradient in the medulla
Only isotonic urine
What is the key step which causes a concentration gradient in the medulla?
Active transport of NaCl
What does the countercurrent multiplier achieve?
- Dilutes by removing NaCl
- 15-20% of intial filtrate removed from loop of henle
- Fluid in tubule more dilute than plasma (hypotonic)
What are the vasa recta?
Arrangement of peritubular capillaries of the juxtamedullary nephrons that participate in the countercurrent mechanism
Why do the vasa recta not drain NaCl in the Loop interstitium?
Hairpin loop arrangement to not interfere with the gradient
What are the functions of the vasa recta?
- Provide medulla O2
- NOT disturb the gradient
- Remove volume from interstitium
