Physiology Of Thirst Flashcards
Hyponatraemia values?
Below 135, severe below 125
Severe symptoms of hyponatraemia?
Confusion drowsiness seizures coma
Headache, nausea mood changes cramps and lethargy
Hyponatraemia classified by extra cellular fluid volume status?
Hypovolaemia: renal loss, non-renal loss
normovalemia: hypothyroidism hypoadrenalism SIADH:
and hypervolaemia: renal failure, cardiac failure cirrhosis
SIADH due to?
High na in urine but low plasma na and low plasma osmolality
Euvolaemic
SIADH causes?
Neoplasia, neurological disorders, Lung diseases and endocrine disorders
SIADH treatment
- Fluid restriction Less than a 1 litre a day
- Demeclocyline induces mild nephrogenic
- Vasopressin antagonists vaptans
Oligodndrocytes degeneration and CNS myelinolysis due to?
Rapid correction of hyponatraemia, particularly in alcoholics and malnourished
Plasma osmolality?
285-295 mosmol/ kg
Variation of urine output?
0.5-2l/ day
Where are osmoreceptors?
Anterior wall of 3rd ventricle
What do osmoreceptors do?
Osmoreceptor cells alter their volume by a transmembrane flux of water in response to changes in plasma osmolality
Where is vasopressin synthesised?
Supraoptic and paraventricular nuclei of hypothalamus
Where are osmoreceptors located?
Anterior wall of 3rd ventricle
ADH action?
Via V2 receptors, cytoplasmic vesicles with aquaporins fuse with membrane,
Causes of poluria and polydipsia?
Exclude diabetes mellitus
- Cranial diabetes- lack of osmoregulated AVP secretion
- Nephrogenic Diabetes- lack of response to renal tubule
- Primary polydipsia-psychogenic
Causes of cranial diabetes?
- Idiopathic 27%
- Genetic- 5% familial mutation of AVP gene
DIDMOAD- diabetes insipidus diabetes melitus optic atrophy and deafness
Recessive - Secondary- post surgical
Traumatic -head injury
Rare causes- tumours, sarcoidosis, meningitis
Hypothalamic syndrome?
Disordered thirst and DI
Hyperphagia
Temperature and sleep disordered
Hypopituatarism
Nephrogenic diabetes causes?
Idiopathic Genetic- mutations of v2 Metabolic- high calcium and low K Drugs lithium Chronic kidney disease
Water deprivation test?
Period of dehydration
Measure plasma and urine osmolalities and weight
Desmopressin injection
Measure again
Treatment of cranial diabetes?
Desmopressin
Nephrogenic diabetes treatment?
Thiazide diuretics and NSAIDs
Classification of hyponatraemia causes?
Drugs-thiazide like diuretics
High conc glucose plasma lipids or proteins
Hypo, normo and hypervolaemia
What is the range of plasma osmolality?
285-295 mosmol/kg
