Regulation of Osmolality Flashcards
What hormone controls water regulation?
ADH aka anti-diuretic hormone
Where is ADH
-synthesised?
-stored?
Synthesised in the hypothalamus
Stored and released from posterior pituitary
What is the half-life of ADH?
10 minutes
->this means it can be rapidly adjusted depending on the body’s need for water
What primarily controls ADH secretion?
Plasma osmolarity
How does plasma osmolality determine the secretion of ADH?
When the osmotic pressure of plasma increased, the release of ADH-secreting hormones from the hypothalamus is increased, which in turns increased release of ADH from the posterior pituitary
->kind of like a negative feedback loop we learned about in endocrine. wordy but read through and understand cos rn I cba xx
What are changes in the neuronal discharge of ADH secreting hormones mediated by?
Osmoreceptors in the anterior hypothalamus
What are osmoreceptors?
Cells which can change their cellular volume in response to osmotic changes
What happens to osmoreceptors if osmolality increases?
Increased water out of cell so cells shrink
What happens to the release of ADH-secreting hormones and ADH when there is high osmolality?
Increased neuronal discharge meaning increased ADH secretion
What happens to osmoreceptors if osmolality decreases?
Water enters cell
Cells swell
What happens to the release of ADH-secreting hormones and ADH when there is low osmolality?
Decreased neuronal discharge meaning decreased ADH secretion
Therefore, what effect does the change in volume of osmoreceptors have?
Leads to changes in osmoreceptor discharge
What is the normal osmolality of plasma?
280-190mOsmoles/Kg water
If osmolality increases due to an increase in NaCl, what happens?
Decreased volume of osmoreceptor
Increased discharge and ADH release
If osmolality increases due to an increase in urea, what happens?
No change in volume, discharge or ADH release
->this is because urea is an ineffective osmole idk gal these slides confuse me
What is the amount of urine produced dependant on?
ADH
Amount of solute to be excreted
Okayyyyy so lets say there was 2400mOsmoles of solute to be excreted, how much urine would be produced?
2 litres
-> maximum urine concentration is 1200-1400mOsmol/L hence why two litres will be produced
Ingestion of hypertonic solutions, like seawater, can cause death. Why?
Increases solute load to be excreted meaning increased urine flow, leading to dehydration and potentially death
->okay just for interest but if you were stuck in the middle of the sea, drinking seawater would actually quicken death!
By addition of aquaporins into the luminal membrane, what effect does this have on permeability of the collecting ducts?
Increases the permeability towards water of the collecting ducts
If ADH is present, how does this effect the permeability of the collecting duct?
ADH increases the permeability for water
What amount/concentration of urine does the presence of ADH produce?
Smaller volume of highly concentrated urine
In the absence of ADH, what happens to the collecting duct’s permeability to water?
Collecting ducts become impermeable to water in absence of ADH
What happens to urine concentration/amount in the absence of ADH?
Larger volume of more dilute urine compensating for water excess as cannot be removed without ADH
So…. what happens to urine if there is excess water?
Want to get rid of water so more dilute, higher quantity of urine
So…. what happens to urine if there is water deficit?
Water wants to be conserved so higher concentration but less quantity of urine
How is urea concentration effected by the presence of ADH?
Presence of ADH means there is movement of water out of the collecting ducts, this greatly concentrates urea remaining in the ducts
In an anti-diuretic situation with high levels of ADH, what happens to urea?
Reabsorbed from the collecting duct into the interstitium where it reinforces the interstitial gradient in the loops of Henle
Why is it important that the urea is reabsorbed from the tubule?
If it remained in the tubule, it would exert osmotic effects to hold water in the tubule and reduce potential for rehydration
As well as osmolarity being a trigger for ADH release, what else has an effect?
ECF volume
If there is increased ECF volume, what happens to the ADH secretion?
Decreased ADH secretion
If there is decreased ECF volume, what happens to the ADH secretion?
Increased ADH secretion
By decreasing ADH, does this promote diuresis or anti-diuresis?
Diuresis
->and vice versa
Control of ADH secretion is linked to the rate of discharge of the stretch receptors in low and high pressures of the circulation.
Where would you find low pressure receptors?
Left and right atria
Great veins
Control of ADH secretion is linked to the rate of discharge of the stretch receptors in low and high pressures of the circulation.
What are the high pressure receptors?
Carotid and aortic arch baroreceptors
Low pressure receptors are sometimes known as volume receptors, why is this?
They monitor the return of blood to the heart and the ‘fullness’ of the circulation
Which receptors are mostly affected by a moderate decrease in ECG volume?
Atrial receptors
What is the subsequent effect of decreased ECF volume on receptor discharge and ADH release?
Decreased ECF -> Decreased Atrial receptor discharge -> Increased ADH release
List some stimuli which can increase release of ADH.
Pain, emotion, stress, exercise, smoking, morphine.
List some stimuli which can decrease release of ADH.
Alcohol
What causes diabetes insipidus?
ADH deficiency
What happens if we don’t have ADH?
Go into a massive diuresis situation
Gal, what is diuresis?
Increased or excessive production of urine
Peripheral diabetes inspipius?
When the collecting duct is insensitive to ADH
Central diabetes insipidus?
Hypothalamus areas synthesising ADH may become damaged or diseased
What can cause damage to the hypothalamic areas synthesising ADH, in turn causing central diabetes insipidus?
Tumours
Meningitis
What are the characteristics of diabetes insipidus?
Passing of very large volumes or dilute urine, often >10L / day
Polydipsia
How can central diabetes insipidus be treated?
Giving ADH
Why can’t ADH be given to treat peripheral diabetes insipidus?
Thirst mechanism required for survival
->idk
What is the average urine output for a day?
1.5L
What is the osmolality of final urine?
50-1200mOsm
In the loop of Henle, how much fluid passes through the Bowman’s capsule each day?
180L
In the loop of Henle, how much fluid passes through the end of the proximal tubule each day?
54L
In the loop of Henle, how much fluid passes through the end of the loop each day?
18L
What is the osmolarity of the fluid in the Bowman’s capsule?
300mOsmoles
What is the osmolarity of the fluid in the end of the proximal tubule?
300 mOsmoles
What is the osmolarity of the fluid in the end of the loop of Henle?
100 mOsmoles
