Vasopressin

Question 1

When is vasopressin released?

Answer 1

High plasma osmolality and hypotension

Question 2

High plasma osmolality is detected… what happens

Answer 2

Magnocellular neurones of SON depolarised
Vasopressin released
Increased water resorption in the distal nephron and collecting duct

Question 3

Describe how the body transmits the message that there is hypotension to the hypothalamus

Answer 3

Baroreceptors detect
Decreased firing of atrial stretch receptors
Less signals transmitted via CN 9 and 10 to hypothalamus (these signals normally inhibit vasopressin release)

Question 4

What happens if the circulating volume is low but of low osmolality?

Answer 4

Volume is preserved over tonicity so vasopressin is released in spite of hyponatraemia

Question 5

Where is vasopressin synthesised?

Answer 5

Magnocellular neurosecretory neurones of the supra-optic nucelus
Paraventricular nucelus

Question 6

Where is vasopressin stored?

Answer 6

Posterior pituitary

Question 7

Where are V1 and V1a vasopressin receptors found and what occurs as a result of their activation?

Answer 7

Vascular smooth muscle (increased vasoconstricive effect in muscle, skin and fat relative to coronary, cerebral and mesenteric)
Platelets - thrombosis is facilitated
Kidneys - vasoconstriction of efferent arterioles so increased renal perfusion

Question 8

Where are V2 receptors found and what happens if they are activated by vasopressin?

Answer 8

Kidneys

AQP2 channels inserted into apical membrane of collecting duct to increase intravascular volume

Question 9

Where are V3/V1b receptors found and what happens when vasopressin activates them?

Answer 9

Anterior pituitary

ACTH is secreted leading to increased plasma cortisol (thought to increase successful defibrillation and chance of ROSC)

Question 10

What is coronary perfusion pressure

Answer 10

Difference in diastolic aortic pressure and end diastolic LV pressure
It’s the pressure gradient that drives coronary blood pressure