Water Balance, Hyponatremia and Diabetes Insipidus Flashcards
What is the main effect of excess water on ADH secretion and thirst?
Decreased thirst and decreased ADH -> reduced intake and increased excretion
What is the main effect of deficit water on ADH secretion and thirst?
Increased thirst, increased ADH –> Increased intake and decreased excretion
What GPCR does ADH bind to on renal tubules?
V2.
What sodium disorder is found in diabetes insipidus?
Hypernatraemia.
What are the main causes of cranial diabetes insipidus?
- Tumours.
- Trauma.
- Infections.
- Idiopathic.
- Genetic - AR.
What are the main causes of nephrogenic diabetes insipidus?
- Osmotic diuresis - diabetes mellitus.
- Drugs.
- CKD.
- Metabolic e.g. hypercalcaemia and hypokalaemia.
Give 5 signs of diabetes insipidus.
- Excessive urine production (>3L/24h).
- Very dilute urine - <300 mOsmol/Kg.
- Severe thirst.
- Hypernatraemia.
- Dehydration.
What investigations might you do to determine whether someone has diabetes insipidus?
- Measure 24-hour urine volume - >3L/24h = suggests DI.
- Plasma biochemisty - hypernatraemia.
- Water deprivation test - urine will not concentrate when asked not to drink.
How is neurological diabetes insipidus treated?
Desmopression
Would you expect a patient with SIADH to be hypovolaemic, euvolaemic or hypervolaemic?
Euvolaemic.
Describe 5 features of the essential criteria for SIADH.
- Hyponatreamia (<135mmol/L).
- Plasma hypo-osmolality.
- High urine osmolality.
- Clinical euvolaemia.
- Increased urinary sodium excretion with normal salt and water intake.
What 3 diseases would be excluded in someone who you suspect could have SIADH.
1) Renal Disease
2) Hypothyroidism
3) Hypocortism
4) Recent diuretic use
Is SIADH associated with Hyponatraemia or Hypernatraemia?
Hyponatraemia <135mmol/L.
Is SIADH associated with plasma hypo-osmolality or hyper-osmolality?
Plasma hypo-osmolality <275mOsm/Kg.
Is SIADH associated with high or low urine osmolality?
High
