Posterior Pituitary Flashcards
Where is the pituitary located
Under the optic chiasm and hypothalamus in the brain
What are the 2 nucleus found in the posterior pituitary
The paraventricular nucleus and the supraoptic nucleus
Where does the posterior pituitary originate
From neuronal tissue- large numbers of glial type cells
What hormones does the posterior pituitary secrete
Vasopressin
Oxytocin
What is the function of vasopressin
It is an anti diuretic hormone which controls water secretion into urine
Where is vasopressin primarily secreted from in the posterior pituitary
The supraoptic nuclei
What is the function of oxytocin
Expression of milk from the glands of the breast to the nipples and promotes the onset of labour
Where is oxytocin primarily secreted from in the posterior pituitary
The paraventricular nuclei
What percentage of the human body is fluid
60%
How much of the 60% fluid sits in the extracellular
33% or 14L which is divided into intravascular at 3.5L and interstitial at 10.5L
How much of the 60% fluid makes up the intracellular fluid
66% or 28L
Where does vasopressin act upon in the nephron
The collecting tubule
What is the mechanism of action for vasopressin
Vasopressin binds to the membrane receptor which activates cAMP which is a secondary messenger system. This inserts aquaporin-2 water pores into the apical membrane meaning more water is absorbed by osmosis into the blood
Where are osmoreceptors found
In the hypothalamus
What doe osmorecptors detect
The change in osmolarity
What do baroreceptors located
Carotid sinus and aortic arch
What do baroreceptors detect
Change in pressure
What happens when you are dehydrated to restore osmolality
Loss of body water increases plasma osmolality which causes increased thirst and increased in AVP neurone firing, this leads to the release of AVP and increased fluid intake, this causes water reabsorption and the restoration of osmolality and circulating sodium concentration
What can affect osmolality
Sodium
Potassium
Chloride
Bicarbonate
Urea
Glucose at high concentrations
Alcohol
Methanol
Polyethylene glycol/mannitol
How can you suppress vasopressin release and thirst
Drinking rapidly
What is polyuria
Large volumes of urine
What is polydypsia
Large volumes of drinking
What is cranial diabetes insipidus
Lack of vasopressin
What is nephrogenic diabetes insipidus
Resistance to vasopressin
What are the 2 types of diabetes insipidus
Cranial and nephrogenic
What can cause cranial diabetes insipidus
Destruction of the hypothalamus
Interruption of the connection of hypothalamus to pituitary
Why could a person get cranial diabetes insipidus
Idiopathic
Tumours
Trauma
Infection
What can caused nephrogenic diabetes insipidus
Osmotic diuresis
Drugs
Chronic renal failure
Post-obstructive uropathy
Metabolic- hypercalcaemia/hypokalaemia
How can you manage cranial diabetes insipidus
Treat any underlying condition
Desmopressin
How can you manage nephrogenic diabetes insipidus
Avoid drugs
High/very high dose of desmopressin
Hydrochlorothiazide
What is SIADH
Syndrome of anti diuretic hormone secretion
Producing ADH when you shouldn’t be producing it
Too much AVP when it should not be being secreted which causes low blood concentration so low osmolality. This causes urine to be inappropriately concentrated and plasma sodium will be low
Patient must be euvolaemia
When does vasopressin start to be secreted
When plasma osmolality gets to 280
How is SIADH managed
Fluid restriction
Sometimes demeclocycline
Vaptans- V2 receptor antagonists
Hypertonic saline
Potential risk of central pontine myelinolysis
