Water balance, diabetes Insipidus and hyponatraemia

Question 1

what is the volume of extracellular fluid in the body?

Answer 1

1/3 of total body water
14L

Question 2

what is the volume of intravascular fluid in the body?

Answer 2

1/4 ECF 3.5 L

Question 3

what is the volume of interstitial fluid in the body?

Answer 3

3/4 ECF 10.5 L

Question 4

what is the volume of intracellular fluid in the body?

Answer 4

2/3 total body water 28L

Question 5

what controls the release of vasopressin ( ADH)?

Answer 5

osmoreceptors
baroreceptors

Question 6

when and where do osmoreceptors control the release of vasopressin ADH ?

Answer 6

in hypothalamus controls release day to day

Question 7

when and where do baroreceptors control the release of vasopressin ADH ?

Answer 7

in brainstem and great vessels release ADH in emergencies

Question 8

define osmolality

Answer 8

concentration per kilo – in plasma very similar to osmolarity but concentration slightly different.

Question 9

what are the causes of cranial diabetes insipidus- lack of vasopressin?

Answer 9

Idiopathic
Trauma
Tumours
Genetic
Vascular – aneurysms, infarction

Question 10

how are cranial diabetes insidious managed

Answer 10

Treat any underlying condition
Desmopressin
Tablets
Nasal spray
Injection

Question 11

define hyponatraemia

Answer 11

serum sodium <135mmol/l

Question 12

define severe hyponatraemia

Answer 12

serum sodium <125mmol/l

Question 13

what is the normal serum sodium range?

Answer 13

137-144 mmol

Question 14

signs and symptoms for hyponatraemia

Answer 14

Headache
Lethargy
Anorexia and abdominal pain
Weakness
Confusion/ hallucinations

Question 15

what tests can you do to test for hyponatraemia?

Answer 15

Plasma osmolality
Urine osmolality
Plasma glucose
Urine sodium
Cortisol

Question 16

what ions does the ECF contain?

Answer 16

large amounts of
sodium
chloride
bicarbonate ions

Question 17

what ions does the ICF contain?

Answer 17

contains potassium, magnesium and phosphate ions

Question 18

During conditions of water excess there is?

Answer 18

1. there is a fall in plasma osmolality, and an influx of water into the cells, increasing the intracellular water content.
2. This reduces thirst and suppresses the release of vasopressin, decreasing water intake and increasing water excretion by the kidney, respectively.
   3.This decreases the amount of water within the body, correcting the water excess.1

Question 19

During conditions of water deprivation there is?

Answer 19

fall in plasma osmolality, and a decrease in cellular hydration.1,2
This stimulates thirst and the release of vasopressin, increasing water intake and reducing water excretion by the kidney.
This increases the amount of water within the body, correcting the water deficit.

Question 20

what is the main driver for fluid intake ?

Answer 20

thirst

Question 21

what are the main drivers of variable water excretion by kidney ( urine output)?

Answer 21

Glomerular filtration rate (GFR)
Vasopressin (AVP)

Question 22

what influences urine concentration and dilution?

Answer 22

Glomerular filtration rate
Sodium reabsorption
Water reabsorption
Vasopressin

Question 23

how does vasopressin directly control water excretion in the kidneys

Answer 23

by binding to the v2 receptor

Question 24

what does the coupling of vasopressin to v2 receptors stimulate?

Answer 24

stimulates an intracellular signalling cascade, leading to the insertion of aquaporins (AQPs) into the apical membrane of the renal collecting duct principle cells

Question 25

what affects osmolality?

Answer 25

sodium, potassium, chloride, bicarbonate, urea and glucose present at high enough concentrations to affect osmolality alcohol, methanol, polyethylene glycol or manitol - exogenous solutes that may affect osmolality

Question 26

what is cranial diabetes insidious

Answer 26

lack of vasopressin AVP deficiency uncommon but life threatening

Question 27

what is nephrogenic diabetes insipidus?

Answer 27

resistance to action of vasopressin app resistance not common but life threatening

Question 28

name 3 diseases associated with the posterior pituitary

Answer 28

cranial diabetes insipidus nephrogenic diabetes insipidu syndrome of anti-diuretic hormone secretion – SIAD