Osmoregulation Flashcards
Where is ADH synthesised?
in the hypothalamus
Where is ADH released?
in the terminals of the hypothalamic neurones found within the posterior pituitary
How does ADH work?
acts in the distal tubule and collecting duct to increase the water permeability by increasing AQP2
How does ADH affect AQP2?
increases the number of AQP2 channels, increasing reabsorption
Before the number of AQP2 channels are increased, where are they stored?
in vesicles inside the epithelial cell (can be quickly inserted into the membrane (quicker mechanism as synthesis not requires))
Why does the osmolality stay the same along the proximal tubule?
even though salt is being reabsorbed so is water so they balance each other out
In terms of urine, what does low osmolality result in?
dilute urine
When is urea production low?
in the presence of selective protein starvation production is low so that the kidney has a lower capacity to concentrate urine
What is the urea transporter and what is it regulated by?
UT-A1
regulated by ADH
When ADH is high, urea absorption is increased, this increases the amount of urea in the extracellular space, increasing water reabsorption
What is the role of urea in the renal medulla?
role in maintaining osmolality
What is osmolality?
defined as the number of osmoles (Osm) of solute per kilogram of solvent
How are the cells of the medulla adapted to survive 1200mOsm? (high osmolality)
to prevent cell swelling, they have to have a high intercellular osmolality. They do this by accumulating a range of organic osmolytes inside the cells. These include: sorbitol, inoitol, glycerophosphorylcholine and betaine
Why does diabetes inspidus?
- due to a loss of ADH secretion (central diabtetes inspidus) or a loss in the sensitivity of the kidney to ADH (usually due to a problem in the V2 receptors) (nephrogenic diabetes insipidus)
- unable to produce concentrated urine
What does diabetes insipidus lead to?
polyuria
dehydration
hypovolaemia
can also cause people to drink too much
How is central diabetes insipidus treated?
uses desmopression (ADH analogue)
How is nephrogenic diabetes insipidus treated?
-low salt diet (prevents high sodium conc)
How is nephrogenic diabetes insipidus caused?
- toxicity
- hypercalceamia
- genetic due to mutations in either V2 or AQP2
What is SIADH?
syndrome of inappropriate ADH (inappropriately high ADH)
What is the urine like of someone with SIADH?
v conc
How do you treat SIADH?
- fluid restriction
- give urea
- V2 receptor antagonist
What happens when there is inadequate water intake?
- increase in osmolality in the plasma
- osmolality is detected in the anteroventral third ventrical (AV3V) region
- AV3V neurones project to the median preoptic area of the hypothalamus which increases thirst
What is the max urine osmolality?
1400mOsm
Can any animals drink sea water?
yes, in rats urine concs can reach 3000mOsm (so can some other animals)
What are the dominant osmolytes in the circulation?
Na+ and Cl- (but aren’t dominat osmolytes ingested e.g carbs, fats and proteins)
When can glucuse conc get so high that it contributes to osmolality?
diabetes mellitus
