Water & Sodium

Question 1

What percentage of body weight is water?

Answer 1

60%

Question 2

What percentage of body weight is intercellular fluid?

Answer 2

40%

Question 3

What percentage of body weight is extracellular fluid?

Answer 3

20%

Question 4

What is interstitial fluid?

Answer 4

Surrounds the cells, but does not circulate

Question 5

What is plasma?

Answer 5

Circulates as the fluid component of the blood

Question 6

What is the main contributor to ECF osmolality and volume?

Answer 6

Sodium

Question 7

What is the predominant cation in ICF?

Answer 7

Potassium

Question 8

What is haemolysis?

Answer 8

When water enters blood cells causing them to expand and burst

Question 9

What is the normal plasma osmolality?

Answer 9

275-295 mmol/kg

Question 10

What are causes of water depletion?

Answer 10

Reduced Intake
Vomiting
Diarrhoea
Diuresis/Diuretics
Sweating

Question 11

Give consequences of dehydration

Answer 11

Thirst
Dry mouth
Inelastic skin
Sunken eyes
Raised haematocrit
Weight loss
Confusion - brain cells
Hypotension

Question 12

What is hyponatraemia?

Answer 12

Excess water

Question 13

What are consequences of hyponatraemia?

Answer 13

Cerebral overhydration
Headaches
Confusion
Convulsions

Question 14

What is hydrostatic pressure?

Answer 14

Pressure difference between plasma and interstitial fluid

Water moves from plasma into interstitial fluid

Question 15

What is oncotic pressure?

Answer 15

Pressure caused by the difference in protein concentration between the plasma and interstitial fluid

Water moves from interstitial fluid into plasma

Question 16

What is oedema?

Answer 16

Excess accumulation of fluid in interstitial space

Disruption of the filtration and osmotic forces of circulating fluids

Obstruction of venous blood or lymphatic return

Inflammation;↑capillary permeability

Loss of plasma protein

Question 17

What is serous effusion?

Answer 17

Excess water in a body cavity

Question 18

What is pathogenesis?

Answer 18

Increased fluid leakage into interstitial spaces OR

Impaired reabsorption of fluid

Question 19

How much fluid does the normal pleural space contain?

Answer 19

10mL of fluid

Question 20

What is essential for pleural effusions to not occur?

Answer 20

Balance between:
- hydrostatic and oncotic forces in the visceral and parietal pleural vessels.
- lymphatic drainage.

Question 21

What is transudate?

Answer 21

Fluid pushed through the capillary due to high pressure within the capillary.

Low protein content

Question 22

What is exudate?

Answer 22

Fluid that leaks around the cells of the capillaries caused by inflammation &↑permeability of pleural capillaries to proteins.

High protein content

Question 23

Why is pleural fluid protein measured?

Answer 23

Measured to differentiate between exudative (eg malignancy, pneumonia) and transudative (eg LVF, cirrhosis, hypoalbuminaemia, peritoneal dialysis) effusions.

Question 24

Do exudates or transudates have higher protein level?

Answer 24

Exudates

Question 25

What is hypernatraemia?

Answer 25

(↑ Na+)
Water deficit:
Poor intake
Osmotic diuresis
Diabetes insipidus

Sodium excess:
Mineralocorticoid (aldosterone) excess
Salt poisoning

Question 26

What is hyponatraemia?

Answer 26

(↓ Na+)
Artefactual

Sodium loss
Diuretics
Addison’s disease

Excess water
IV fluids (iatrogenic)
SIADH

Excess water ++ and sodium +
Oedema