SIADH Flashcards
What does SIADH stand for
Syndrome of Inappropriate Anti-Diuretic Hormone (SIADH)
What is the definition of Syndrome of Inappropriate Anti-Diuretic Hormone (SIADH)
Characterised by excess release of ADH leading to retention of water and hyponatraemia
ADH = Causes water
a) reabsorption
b) excretion
a) reabsorption
Define plasma osmolality
Refers to the concentration of dissolved particles in a body of fluid.
If plasma osmolality is high what does this mean?
Means there are more particles or less fluid.
What is the function of ADH excess
ADH excess results in reduced diuresis - water excretion and urinary output are reduced
This leads to an increase in total body water which dilutes the sodium concentration causing hyponatraemia.
What is the other name for Anti-Diuretic Hormone (ADH)
Vasopressin
What produces ADH
Produced in the hypothalamus
Where is ADH stored and secreted
Posterior pituitary gland
ADH is released in response to what?
Rising plasma osmolality
ADH stimulates water reabsorption from where?
The collecting ducts and distal convoluted tubule in the kidneys
How does ADH cause water reabsorption
ADH stimulates water reabsorption from the collecting ducts and distal convoluted tubule in the kidneys
ADH stimulates the insertion of aquaporin-2 channels onto the luminal membrane, allowing the free entry of water
Define paraneoplastic syndrome
When autoimmune disorders are triggered by tumours.
Give examples of autoimmune conditions that can cause paraneoplastic syndrome
Cushing’s syndrome
SIADH
Lambert-Eaton syndrome
Hyperparathyroidism
Name some causes of SIADH
Either the posterior pituitary is secreting too much ADH or ADH is being produced somewhere else e.g. small cell lung cancer
- Malignancy – small cell lung cancer (paraneoplastic syndrome)
- Recent major surgery
- CNS – stroke, SAH, head injury
- Infection – TB, pneumonia
- Drugs – sulfonylureas, SSRIs
