Water & Sodium Flashcards
What percentage of body weight is water?
60%
What percentage of body weight is intercellular fluid?
40%
What percentage of body weight is extracellular fluid?
20%
What is interstitial fluid?
Surrounds the cells, but does not circulate
What is plasma?
Circulates as the fluid component of the blood
What is the main contributor to ECF osmolality and volume?
Sodium
What is the predominant cation in ICF?
Potassium
What is haemolysis?
When water enters blood cells causing them to expand and burst
What is the normal plasma osmolality?
275-295 mmol/kg
What are causes of water depletion?
Reduced Intake
Vomiting
Diarrhoea
Diuresis/Diuretics
Sweating
Give consequences of dehydration
Thirst
Dry mouth
Inelastic skin
Sunken eyes
Raised haematocrit
Weight loss
Confusion - brain cells
Hypotension
What is hyponatraemia?
Excess water
What are consequences of hyponatraemia?
Cerebral overhydration
Headaches
Confusion
Convulsions
What is hydrostatic pressure?
Pressure difference between plasma and interstitial fluid
Water moves from plasma into interstitial fluid
What is oncotic pressure?
Pressure caused by the difference in protein concentration between the plasma and interstitial fluid
Water moves from interstitial fluid into plasma
What is oedema?
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
What is serous effusion?
Excess water in a body cavity
What is pathogenesis?
Increased fluid leakage into interstitial spaces OR
Impaired reabsorption of fluid
How much fluid does the normal pleural space contain?
10mL of fluid
What is essential for pleural effusions to not occur?
Balance between:
- hydrostatic and oncotic forces in the visceral and parietal pleural vessels.
- lymphatic drainage.
What is transudate?
Fluid pushed through the capillary due to high pressure within the capillary.
Low protein content
What is exudate?
Fluid that leaks around the cells of the capillaries caused by inflammation &↑permeability of pleural capillaries to proteins.
High protein content
Why is pleural fluid protein measured?
Measured to differentiate between exudative (eg malignancy, pneumonia) and transudative (eg LVF, cirrhosis, hypoalbuminaemia, peritoneal dialysis) effusions.
Do exudates or transudates have higher protein level?
Exudates
What is hypernatraemia?
(↑ Na+)
Water deficit:
Poor intake
Osmotic diuresis
Diabetes insipidus
Sodium excess:
Mineralocorticoid (aldosterone) excess
Salt poisoning
What is hyponatraemia?
(↓ Na+)
Artefactual
Sodium loss
Diuretics
Addison’s disease
Excess water
IV fluids (iatrogenic)
SIADH
Excess water ++ and sodium +
Oedema
