1: Sodium and water balance

Question 1

How is [Na⁺] calculated?

Answer 1

[Na⁺] = mmol Na⁺ / L H₂O

Question 2

What is the reference range of [Na⁺]?

Answer 2

135 - 145 mmol/L

Question 3

What level of Na⁺ indicates hyponatraemia?

Answer 3

< 120 mmol/L

Question 4

What are the two possible mechanisms of hyponatraemia?

Answer 4

Decrease in [Na⁺]

OR

Increase in [H₂O]

Question 5

___ follows sodium everywhere it goes.

Answer 5

Water

Question 6

What are the symptoms of hyponatraemia caused by a decrease in sodium concentration?

Answer 6

“Dry” symptoms:

Tachycardia

Postural hypotension

Dry mucuous membranes

Reduced urine output

Decreased level of consciousness

Question 7

What is the main symptom of hyponatraemia due to increase in water concentration?

Answer 7

Increase in ECF and ICF volume, producing peripheral oedema

Question 8

The volume of the ECF is ___ the volume of the ICF.

Answer 8

half

Question 9

The volume of the ICF is ___ the volume of the ECF.

Answer 9

double

Question 10

In terms of the ICF and ECF, where is

a) water
b) sodium found?

Answer 10

a) Water is found in both ECF and ICF

b) Sodium is only found in ECF (by action of sodium-potassium pump)

Question 11

How are the two types of hyponatraemia treated?

Answer 11

Too much water ⇒ Fluid restrict

Too little sodium ⇒ Give sodium

Question 12

How is sodium homeostasis maintained?

Answer 12

Mineralocorticoids (aldosterone)

Question 13

Which gland produces mineralocorticoids like aldosterone?

Answer 13

Zona glomerulosa of the adrenal cortex

Question 14

How do mineralocorticoids maintain sodium homeostasis?

Answer 14

Cause sodium reabsorption in the distal convoluted tubules of the kidneys

Question 15

Which mineralocorticoid causes sodium retention in response to hypotension?

Answer 15

Aldosterone

RAAS

Question 16

What happens when mineralocorticoids are produced in excess?

Answer 16

Sodium retention > Water retention > Hypernatraemia/volaemia

Question 17

What happens when mineralocorticoids are deficient?

Answer 17

Sodium loss > Water loss > Hyponatraemia/volaemia

Question 18

How is water homeostasis maintained?

Answer 18

ADH

Question 19

Which gland secretes ADH?

Answer 19

Posterior pituitary

Question 20

How does ADH maintain water homeostasis?

Answer 20

Promotes water reabsorption in the collecting ducts of the kidneys

Question 21

What is the concentration of urine also known as?

Answer 21

Urine osmolality

Question 22

ADH excess produces ___ urine and therefore a (high/low) urine osmolality.

Answer 22

ADH excess

concentrated urine

high urine osmolality

Question 23

ADH deficiency produces ___ urine and therefore a (high / low) urine osmolality.

Answer 23

ADH deficiency

dilute urine

low urine osmolality

Question 24

What condition causes ADH excess, excess water reabsorption and hyponatraemia?

Answer 24

SIADH

Question 25

What level of Na⁺ indicates hypernatraemia?

Answer 25

> 160 mmol/L

Question 26

What can cause an increase in sodium levels leading to hypernatreamia?

Answer 26

Conn’s syndrome

IV drugs

Near-drowning

Question 27

What can cause water loss leading to hypernatraemia?

Answer 27

Diabetes insipidus

Profuse vomiting (e.g DKA)

Inadequate H₂O intake

Question 28

How is water loss hypernatreamia treated?

Answer 28

Give water

Question 29

How is hypernatraemia caused by sodium excess treated?

Answer 29

Loop diuretics

(To cause natriuresis)