Physiology Of Thirst

Question 1

Hyponatraemia values?

Answer 1

Below 135, severe below 125

Question 2

Severe symptoms of hyponatraemia?

Answer 2

Confusion drowsiness seizures coma

Headache, nausea mood changes cramps and lethargy

Question 3

Hyponatraemia classified by extra cellular fluid volume status?

Answer 3

Hypovolaemia: renal loss, non-renal loss
normovalemia: hypothyroidism hypoadrenalism SIADH:

and hypervolaemia: renal failure, cardiac failure cirrhosis

Question 4

SIADH due to?

Answer 4

High na in urine but low plasma na and low plasma osmolality

Euvolaemic

Question 5

SIADH causes?

Answer 5

Neoplasia, neurological disorders, Lung diseases and endocrine disorders

Question 6

SIADH treatment

Answer 6

1. Fluid restriction Less than a 1 litre a day
2. Demeclocyline induces mild nephrogenic
3. Vasopressin antagonists vaptans

Question 7

Oligodndrocytes degeneration and CNS myelinolysis due to?

Answer 7

Rapid correction of hyponatraemia, particularly in alcoholics and malnourished

Question 8

Plasma osmolality?

Answer 8

285-295 mosmol/ kg

Question 9

Variation of urine output?

Answer 9

0.5-2l/ day

Question 10

Where are osmoreceptors?

Answer 10

Anterior wall of 3rd ventricle

Question 11

What do osmoreceptors do?

Answer 11

Osmoreceptor cells alter their volume by a transmembrane flux of water in response to changes in plasma osmolality

Question 12

Where is vasopressin synthesised?

Answer 12

Supraoptic and paraventricular nuclei of hypothalamus

Question 13

Where are osmoreceptors located?

Answer 13

Anterior wall of 3rd ventricle

Question 14

ADH action?

Answer 14

Via V2 receptors, cytoplasmic vesicles with aquaporins fuse with membrane,

Question 15

Causes of poluria and polydipsia?

Answer 15

Exclude diabetes mellitus

1. Cranial diabetes- lack of osmoregulated AVP secretion
2. Nephrogenic Diabetes- lack of response to renal tubule
3. Primary polydipsia-psychogenic

Question 16

Causes of cranial diabetes?

Answer 16

1. Idiopathic 27%
2. Genetic- 5% familial mutation of AVP gene
   DIDMOAD- diabetes insipidus diabetes melitus optic atrophy and deafness
   Recessive
3. Secondary- post surgical
   Traumatic -head injury
   Rare causes- tumours, sarcoidosis, meningitis

Question 17

Hypothalamic syndrome?

Answer 17

Disordered thirst and DI
Hyperphagia
Temperature and sleep disordered
Hypopituatarism

Question 18

Nephrogenic diabetes causes?

Answer 18

Idiopathic
Genetic- mutations of v2
Metabolic- high calcium and low K
Drugs lithium
Chronic kidney disease

Question 19

Water deprivation test?

Answer 19

Period of dehydration
Measure plasma and urine osmolalities and weight
Desmopressin injection
Measure again

Question 20

Treatment of cranial diabetes?

Answer 20

Desmopressin

Question 21

Nephrogenic diabetes treatment?

Answer 21

Thiazide diuretics and NSAIDs

Question 22

Classification of hyponatraemia causes?

Answer 22

Drugs-thiazide like diuretics
High conc glucose plasma lipids or proteins
Hypo, normo and hypervolaemia

Question 23

What is the range of plasma osmolality?

Answer 23

285-295 mosmol/kg