Endo - Disorders of vasopressin

Question 1

action of vasopressin ?

(there are three actions)

Answer 1

• also known as anti diuretic hormone
• stimulates water reabsorption in renal collecting duct
• concentrating urine
• acts thru V2 recep in kidney
• acts via V1 recep to vasoconstrict
• stimulates ACTH release from ant pit

Question 2

what does post pit look like on MRI?

if not visualised what does it mean?

Answer 2

Question 3

What is osmolality ?

Answer 3

conc of sodium in serum

low osmolality -more dilute- more water

Question 4

stimuli for vasopressin release ?

Answer 4

osmotic

• inc plasma osmolality detected by osmoreceptors

Non osmotic

• decr atrial pressure sensed by atrial stretch recep

Question 5

Vasculature of osmotic stimulation?

Answer 5

Two nuclei which sit at 3rd ventricle :

• organum vasculosum
• subfornical organ

no blood brain barrier - neurones resond to changes in systemic circ

highly vascularised

neurones project to supraoptic nucleus - site of vasopressinergic neurons

Question 6

how do osmoreceptors regulate vasopressin

Answer 6

1. inc in extracellular Na
2. osmoreceptors shrink
3. inc osmorecep firing
4. AVP release form hypothalamic neurones

Question 7

how do atrial strech recep regulate vasopressin release ?

Answer 7

• atrial strech recep detect pressure in right atrium
• inhibits vasopressin release via vagal afferents to hypoth
• reduction in circ volume eg haemorrhage –> less inhib

Question 8

why is vasopressin released after haemorrhage

Answer 8

• via kidney V2 recep increased water reabsorption - restores some circulating volume
• via V1 recep vasoconstriction