Disorders of Vasopressin Flashcards
The posterior pituitary is composed of what type of tissue and is anatomically continuous with what structure?
neural tissue, anatomically continuous with the hypothalamus
What type of neurons are found in the posterior pituitary and what do they contain?
Hypothalamic magnocellular neurons containing either oxytocin or AVP
describe the structure of the neurones in the posterior pituitary
long, originating in supraoptic and paraventricular nuclei. nuclei-stalk-posterior pituitary
What is the other name for vasopressin?
Anti-diuretic hormone (ADH)
What are the physiological actions of ADH/ vasopressin?
Stimulation of water reabsorption in the renal collecting duct to concentrate urine through the V2 receptor in the kidney. vasoconstrictor through V1 receptors, stimulates ACTH release from anterior pituitary.
How does Vasopressin concentrate urine?
AVP binds to V2 receptor in the collecting duct. this stimulates an intracellular cascade, promoting the movement of aquaporin-2 into the apical membrane. Water moves out of cell via aquaporin-3 on basolateral membrane into plasma creating more concentrated urine.
What happens when AVP binds to V2 receptors to promote aquaporin-2 movement into the apical membrane?
AVP binds to V2, a G-coupled receptor. the G protein unit binds with adenylate cyclase producing c-AMP which activates protein kinase A, protein kinase a causes transcription and insertion of aquaporin-2 into membrane.
How is the posterior pituitary visualised on an MRI?
visualized as a bright spot however not visualized in all healthy individuals so absence could be normal variation
what are the two types of stimulus for vasopressin release?
osmotic and non-osmotic
what is the osmotic stimuli for the release of vasopressin?
rise in plasma osmolality sensed by osmoreceptors
What structures are involved in the osmotic stimulation of vasopressin release?
Organum vasculosum and subfornical organ. both nuclei which sit around the 3rd ventricle.
what features of the organum vasculosum and subfornical organ aid them in the stimulation of vasopressin release?
are circumventricular, have no blood brain barrier so neurons can respond to changes in the systemic circulation. are highly vascularised. nuerones project to the supraoptic nucleus, the site of vasopressinergic neurons
Describe the process of the osmotic stimulation of vasopressin release
increase in extracellular Na+, causes water to move out of osmoreceptors. this causes osmoreceptor shrinkage resulting in increased osmoreceptor firing to supraoptic nuclei. AVP is released from hypothalamic neurons
what is the non-osmotic stimuli for vasopressin release?
decrease in atrial pressure sensed by stretch receptors
outline the process of non-osmotic stimulation of vasopressin release
atrial stretch receptors detect pressure in right atrium and act to inhibit vasopressin release via vagal afferents to hypothalamus causing a reduction in circulating volume. A lower pressure results in less inhibition of vasopressin release resulting in increased water resorption and vasoconstriction
why is vasopressin released following a haemorrhage? what other system will play an important role in control of BP?
to increase water reabsorption in the kidney and vasoconstriction. the renin-angiotensin system will also be important through detection via the juxtaglomerular apparatus.
Outline the physiological response to water deprivation
plasma osmolality increases causing stimulation of osmoreceptors. This causes the feeling of thirst and increases AVP release. Water reabsorption from the renal collecting ducts increases reducing the volume of urine but increasing the urine osmolality. This results in a reduction in plasma osmolality
What is the foundational difference between diabetes insipidus and diabetes mellitus?
diabetes insipidus is due to an issue with vasopressin not insulin/glucose
what is the cause of diabetes insipidus?
a problem with the hypothalamus and/or posterior pituitary resulting in the inability to make AVP
what are the two types of diabetes insipidus?
Cranial diabetes insipidus - Vasopressin insufficiency. a problem with the hypothalamus or posterior pituitary so that AVP isnt produced. Nephrogenic diabetes insipidus - Vasopressin resistance. the kidneys are unable to respond to vasopressin
what are the hallmark symptoms of diabetes insipidus?
polyuria, nocturia, polydipsia, thirst.
is diabetes insipidus or diabetes mellitus more common?
diabetes mellitus
is CDI or NDI more common?
CDI
What are the causes of cranial diabetes insipidus?
Acquired: traumatic brain injury, pituitary surgery, pituitary tumours, metastasis to the pituitary gland, granulomatous inflammation of pituitary stalk, autoimmune.
congenital
