3.4. Regulation of Osmolarity - Concentrating Ability of the Kidney Flashcards
What does the amount of urine produced depend on?
- ADH concentration
2. The amount of solute to be excreted
What would happen if the amount of solute needed to be excreted was 2400mOsmoles?
You would excrete 2 litres of urine
Was does ingestion of hypertonic solutions cause?
The increase of the solute load to excrete, therefore increasing the urine flow.
What can ingestion of hypertonic solutions lead to?
Dehydration as more H2O is required to excrete the solute load than was ingested with it - people trapped at sea die quicker from drinking sea water
Where is the site of water regulation?
At the collecting duct
What controls the permeability of the collecting duct?
ADH (Vasopressin)
What does ADH (Vasopressin) acting on a protein cause?
Aquaporins (H2O channels), which are stored on vesicles in the luminal cells, to migrate to the surface as a secondary cascade - increasing the permeability
What happens if ADH is present?
H2O is able to leave the collecting duct
What is a result of H2O being able to leave the collecting duct, as a result of ADH?
The cortical part of the collecting duct equilibrates with the cortical part of the interstitium
Where does the collecting duct travel?
It passes through the medullary (hypertonic) interstitial gradient
What creates the medullary interstitial gradient?
The counter-current multiplier of the loop of henle
What happens if maximum ADH concentration is present?
The contents of the collecting duct equilibrate with the medullary interstitium, via osmotic efflux of H2O, and thus a small volume of highly concentrated urine is produced
What does the small volume of highly concentrated urine, produced in the collecting duct at maximum ADH concentration, contain?
Relatively less of the filtered H2O than the solute, compensating for the water deficit
What is the overall effect of maximum concentrations of ADH being present?
This effectively adds H2O to the ECF as the H2O is reabsorbed, by the oncotic pressure, into the Vasa Recta
What happens in the absence of ADH?
- The collection ducts are impermeable to H2O
2. So a large volume of Dilute Urine is produced - compensating for the H2O excess
