Disorders of Vasopressin Flashcards
What type of tissue is the posterior pituitary?
Neural tissue. anatomically continuous with hypothalamus.
What is the posterior pituitary made up of?
Hypothalamic magnocellular neurons, that are long and originate in the supraoptic and paraventricular hypothalamic nuclei.
What are the two main hormones in the posterior pituitary?
Arginine Vasopressin (AVP), Oxytocin.
What receptor does AVP act through in the kidney?
V2 receptor - stimulation of water reabsorption.
V1 receptor - vasoconstriction, ACTH release.
What is the main stimulus for the release of ACTH from the posterior pituitary?
CRH
Is it normal not to see the posterior pituitary (bright spot) in an MRI?
Yes, not visible in all healthy individuals.
What are the stimuli for Vasopressin release?
Osmotic - Rise in plasma osmolarity sensed by osmoreceptors.
Non-osmotic - Decrease in atrial pressure sensed by atrial stretch receptors.
What groups of cells sense plasma osmolarity?
Organum vasculosum
Subfornical organ
What is special about the Organum vasculosum & Subfornical organ?
- both nuclei which sit around the 3rd ventricle
(‘circumventricular’) - no blood brain barrier – so neurons can respond to
changes in the systemic circulation - highly vascularised
- neurons project to the supraoptic nucleus - site of
vasopressinergic neurons
How do Osmoreceptor’s regulate vasopressin?
Increase in extracellular Na+ Water flows out of Osmoreceptor Osmoreceptor shrinks Change in shape triggers osmoreceptor firing AVP release from hypothalamic neurons
Describe Non-Osmotic stimulation of vasopressin release?
Atrial stretch receptors detect pressure in the right atrium,
Inhibit vasopressin release via vagal afferents to hypothalamus,
Reduction in circulating volume eg haemorrhage means less stretch of these atrial receptors, so less inhibition of vasopressin.
What is the difference between diabetes mellitus and diabetes insipidus?
Symptoms that typically present due to diabetes mellitus, do so due to osmotic diuresis whereas in diabetes insipidus it is due to problems with vasopressin.
What are the two types of diabetes insipidus?
Cranial
Nephrogenic
What happens in Cranial diabetes insipidus?
Problem with hypothalamus &/or posterior pituitary
Unable to make arginine vasopressin
‘VASOPRESSIN INSUFFICIENCY’
What happens in Nephrogenic diabetes insipidus?
Can make arginine vasopressin (normal hypothalamus & posterior pituitary)
Kidney (collecting duct) unable to respond to it
‘VASOPRESSIN RESISTANCE’