1b Disorders of Vasopressin Flashcards
What is the physiological action of vasopressin?
Stimulation of water reabsorption into the renal collecting duct = concentrates the urine
Which receptor does AVP work through?
V2 receptor in the kidney
How does AVP work as a vasoconstrictor?
Via the V1 receptor
Describe how AVP concentrates the urine?
- AVP binds to V2 receptor on basolateral membrane
- This triggers intracellular cascade resulting in the movement of aquaporin-2 molecules onto the apical membrane
- this allows the movement of water from the urine into the blood, therefore concentrating it
What is the bright spot on an MRI of the pituitary?
Posterior Pituitary
What are the two stimuli for vasopressin release?
Osmotic and Non-osmotic
Describe how the osmotic stimuli for vasopressin release works?
rise in plasma osmolality detected by osmoreceptors
Describe how the non-osmotic stimuli for vasopressin works?
decrease in atrial pressure sensed by atrial stretch receptors
What are the names of the nuclei from which AVP is released?
Organum vasulosum and subfornical organ
What enables the organum vasculosum and subfornical oragn to respond to changes in systemic circulation?
Highly vascularised and no blood brain barrier
Where do the neurones of the organosum vasculosum and subfornical organ project to?
the supraoptic nuclei
Describe how osmoreceptors regulate vasopressin?
- Increase in extracellular sodium
- Therefore movement of water out the osmoreceptor by diffusion
- Osmoreceptor shrinks
- This increases osmoreceptor firing
- More osmoreceptor firing leads to more AVP release from the hypothalamic neurones
Describe how the non-osmotic stimulation of Vasopressin works?
- stretch receptors in atrium detect pressure and INHIBIT RELEASE
- Therefore when the volume drops, the stretch receptors are stretched less, so LESS INHIBITION OF VASOPRESSIN
What might trigger the non-osmotic stimulation of Vasopressin Release?
Major haemorrhage
What are the benefits of vasopressin release following major haemorrhage?
- Increase the circulating volume
- Restore the blood pressure which will have dropped
How doe AVP trigger an increase in blood volume following haemorrhage?
Increased water absorption in the kidney via V2 receptor, therefore increasing blood volume and hence pressure as well
Which receptors does AVP initiate vasoconstriction through?
V1 receptors
What is the physiological response to water deprivation?
- Increased plasma concentration
- This stimulates the osmoreceptors to fire, leading to AVP release
- This stimulates water reabsorption from the renal collecting ducts
- Urine volume decreases, and the concentration of the urine increases as more water is kept
- This reduces the plasma concentration