Endo - Vasopressin Flashcards
What is the other name of AVP?
→ argenine vasopressin
→ anti-diuretic hormone
What is the main physiological action of AVP?
Stimulation of water reabsorption in the renal collecting duct
What impact does vasopressin have on urine?
Concentrates urine
What is another purpose of AVP?
→ Vasoconstrictor
→ stimulates ACTH release from anterior pituitary
By what mechanism does AVP concentrate urine?
→ acts on V2 receptors in kidney
→ after the cascade of proteins, aqua-porin 2 + transports the H2O from the urine into cells
→ aqua-porin 3 transports it back to plasma
How does vasopressin act as a vasoconstrictor?
Via v1 receptor
How does posterior pituitary show up on MRI?
“bright spot” but not visualised in all healthy individuals
What is the osmotic stimuli for vasopressin release?
Rise in plasma osmolality sensed by osmoreceptors
What is the non-osmotic stimuli for vasopressin release?
Decrease in atrial pressure sensed by atrial stretch receptors
What are the nuclei that respond to the osmotic stimuli?
→ organum vasculosum
→ subfornical organ
Where are the two nuclei located?
Around the 3rd ventricle “circum ventricular”
What makes the two nuclei good at responding to osmotic stimuli?
→ no blood brain barrier, neurones respond to change into systemic circulation
→ highly vascularised + has osmoreceptors
→ neurones project to the supraoptic nucleus - site of vasopressinergic neurones
How do osmoreceptors regulate vasopressin?
→ osmoreceptors respond to increase in extracellular Na+ causing water to exit
→ osmoreceptor shrinks
→ osmoreceptor firing increases
→ AVP released from hypothalamic neurones
How does the mechanism of non-osmotic stimulation of vasopressin work?
→ atrial receptors detect pressure in right atrium
→ inhibit vasopressin release via vagal afferent to hypothalamus
→ reduction in circulating volume e.g. haemorrhage, means less stretch of these atrial receptors
→ leads to less inhibition of vasopressin
Why is vasopressin released after a haemorrhage?
→ to restore some circulating volume
→ vasopressin release = increased water reabsorption in kidneys + vasoconstriction