Water and Sodium Flashcards
what is the distribution of water in the body?
60% of mass = water
20% Extracellular (more interstitial - less intravascular)
40% intracellular
7% plasma
interstitial fluid + plasma = what?
extracellular fluid
what does isotonic mean?
osmolality is the same
what part of the brain watches plasma osmolarlity?
the hypothalamus
what does ECF contain?
sodium, chloride, bicarbonate, glucose, urea,
what does ICF contain?
predominantly potassium
what is the equation for plasma osmolality?
2[Na] + 2[K] + urea + glucose mmol/L
what effect on plasma osmolality does alcohol have?
alcohol increases plasma osmolality
what is normal ECF osmolality?
275-295 mmol/kg
why is water not given intravenously?
water is hypotonic vs cells - would cause haemolysis of blood cells
what happens when someone is deprived of water?
there is an increase in ECF osmolality.
water moves from ICF to ECF - and the hypothalamus activates the ‘thirst centre’
releases ADH from posterior pituitary
renal water retention (less wee)
what controls ECF volume?
the renin-angiotensin-aldosterone system
what is renin?
a kidney enzyme that acts on the protein angiotensin to form angiotensin 1
what synthesises aldosterone?
the adrenal cortex
what does aldosterone do?
promotes sodium reabsoprtion and potassium secretion
what is angiotensin 2?
a vasoconstrictor
what happens when there is excess water in the body?
ECF osmolality decreases.
water moved into the ICF, and ADH is inhibited from the posterior pituitary gland.
what is volume overload?
ECF volume expansion
what can volume overload cause?
heart failure, loss of intravascular fluid into interstitial space low effective circulation volume renal sodium retention + water retention loss of plasma protein
what is oedema?
the accumulation of extra interstitial fluid - which disrupts filtration and osmotic forces.
what is hydrostatic pressure?
the pressure exerted by fluid in equilibrium - caused by the heart
what is oncotic pressure?
a form of pressure caused by proteins in fluid - mostly albumin
how does oncotic pressure work?
proteins in capillaries can’t move across the well and thus pull water back into circulation
what is serous effusion?
excess water in a body cavity
what is pathogenesis?
increased fluid leakage into interstitial space or impaired reabsorption of fluid.
what is venous oedema?
a blockage at one end which pushes water into the interstitial fluid
what is lymphatic oedema?
when the lymphatic system is blocked and water builds up in the interstitial fluid
what is hypalbuminaemic oedema?
low proteins, so can’t reabsorb the water as there are no proteins to pull the water back in.
what is pleural effusion?
when the balance between hydrostatic and oncotic forces in the visceral and parietal pleural vessels is off so the pleural space becomes filled with more fluid.
what is transudate?
when the fluid is pushed through the capillary due to high pressure within the capillary - low protein in the extravascular fluid
