Pituitary Flashcards
How does hormone secretion by the posterior pituitary become stimulated? and what hormones does it secrete?
Stimulated via a neuronal link with the hypothalamus. The posterior pituitary secretes vaspopressin and oxytocin
Name some examples of oxytocins actions? When is the rate of secretio highest?
Contraction of the womb during lactation and childbirth. Aiding in contraction of seminal vesicles of the testis and increase lipolysis in the adipocytes. Increased response during suckling and end of pregnancy.
How is the AVP precursor modified?
The post translational modification cleaves the signal peptide (N-terminus) and a glycoprotein (C-terminus).
AVP is released in response to…..
A decrease in plasma volume or increase in plasma osmolality
Describe the actions of AVP
AVP act on either V1R, to increase vascular resistance, or V2R, to increase blood volume, which both results in increased arterial pressure.
Name some conditions associated with inappropriate secretion of AVP
Syndrome of inappropriate antidiuresis (SIADH) and diabetic insipidus (cranial and nephrogenic)
Describe the biochemical characterisation of SIADH
Nomovolaemic (normal BP) hyponatraemia (low serum Na)
Name some causes of SIADH with the
It can be caused by drugs (NSAIDs, opiates), CNS disorders (stroke, trauma), or a hereditary defect in the AVP receptors.
How is SIADH diagnosed?
SIADH is diagnosed by exclusion
What is the criteria for diagnosing SIADH?
Euvolemic hyponatraemia Low serum osmolality (<275mOsm/kg) Urine sodium > 25mmol/L Urine osmolality >100mOsm/kg No renal, adrenal or thyroid disease
What is the treatment of SIADH?
Firstly attempt to remove the cause if possible (e.g. drugs). Restrict water intake (500-750mL/day), increase solute intake, using low dose loop diuretic with oral sodium chloride.
How does the AVP production biochemically present in diabetes insipidus?
The lack of AVP production causes polydipsia, or lack of response of AVP causing polyuria.
What happens when a patient with diabetes insipidus does not have free access to water?
Develop dehydration and hypernatraemia
What is the difference between cranial and nephrogenic DI?
Cranial: lack of AVP production
Nephrogenic: normal AVP production, but kidney does not respond
How can DI be assessed?
Typically use water deprivation test, where at 0800 the weight and urine + serum osmolality samples are taken. Commence fluid restriction. Hourly the patient is weighed and take urine and serums samples for osmolality. The test needs to be aborted if the fall in weight is greater than 5% or serum osmolality rise above 300mosm/kg (dangerously dehydrated)
When should a desmopressin test be administered?
The desmopressin test will be done following the water deprivation test if urine osmolality is still <750mosm/kg after 8h fluid restriction