5. Neurohypophysis Disorders Flashcards
Mechanism of vasopressin
Binds to V2 receptors in collecting duct cells
adenylyl cyclase -> cAMP -> activates PKA
Leads to synthesis of AQP2
Aggraphores migrate and insert onto apical membrane
Water can flow in and go into the blood via AQP3/4 channels in basolateral membrane
How is vasopressin secretion regulated?
Osmoreceptors in organum vasculosum
Project to PVN + SON in hypothalamus
High EC Na -> osmoreceptor shrinks -> increased firing to hypothalamus
What are the types of diabetes insipidus?
Cranial = Absence/lack of ADH Nephrogenic = Kidneys are resistant to ADH
What drug can cause nephrogenic DI?
Lithium
Signs/symptoms of DI?
Polyuria + polydipsia
Hypo-osmolar (diluted) urine
Dehydration -> death
Possible disruption to sleep
What is psychogenic polydipsia?
Polydipsia + polyuria BUT ability to secrete vasopressin is NORMAL
Usually seen in patients who have been asked to drink a lot by doctors, or due to anti-cholinergic drugs causing dry mouth
What would you expect to see in plasma osmolality of psychogenic polydipsia and DI patients?
PPD - LOW osmolality
DI - HIGH osmolality (less water)
Biochemical features of DI
Hypernatraemia
Raised urea
Increased plasma osmolality
Dilute (hypo-osmolar) urine
Treatment of cranial DI
Desmopressin (DDAVP)
Treatment of nephrogenic DI
Thiazide diuretics (possible increase in proximal tubule water reabsorption)
What is SIADH
Syndrome of Inappropriate ADH (i.e. HIGH ADH)
Signs of SIADH
Generally symptomless
Initial raised urine osmolality, low urine volume
HYPOnatraemia
What happens if plasma Na drops to <120mM
Weakness, poor mental function, nausea
What happens if plasma Na drops to <110mM
Confusion -> Coma -> DEATH
Causes of SIADH
CNS (stroke, tumour) Pulmonary disease (pneumonia) Malignancy (lung small cell) Drugs (SSRIs, carbamazepine) Idiopathic
