water balance Flashcards
why do we need h20
1) universal solvent
2) chemical reactions
3) major component of cells and plasma
4) lubricant of joints, organs
what are 3 valuable features of water
1) high ability to absorb and retain heat
2) large amount of heat required to increase its temp
3) sweating carries a lot of heat away from the body
how many litres of water does the average body contain and where is it distributed
32-40 litres
intracellular fluid - 25L
interstitial fluid - 12L
extracellular fluid - 3L
what is the body made up of in terms of water, fat, protein, carbohydrates, minerals
water - 60% fat - 18% protein - 16% minerals - 5.2% carbohydrates - 0.7%
define simple diffusion
movement from an area of high concentration to an area of low concentration through a semipermeable membrane - passive
what factors effect diffusion - 5 things
1) temperature
2) molecular weight
3) steepness of concentration gradient
4) membrane surface
5) membrane permiability
define osmosis
diffusion of water from high concentration to low concentration - passive
what is a solution
a homogenous mixture of one or more dissimilar substances
usually a liquid (solvent) and a solute (electrolyte particle)
what are the 3 types of solution
1) aqueous - small molecules dissolve
2) colloids - proteins or other large molecules
3) suspensions - even larger molecules
define osmotic pressure and give an example
the force (thrust) of water movement into the higher concentration solution
or
the amount of hydrostatic pressure required to stop osmosis
e.g glucose can exert pressure by drawing water towards it
how can you measure concentration of solutes
g/L weight per volume
%
moles per L (moles =number of molecules present in a sample)
why moles
in physiology the number of molecules in solution is more important than % or weight
define osmolarity, what does osmolality effect
number of osmoles/L solution
e.g 500 osmoles more concentrated than 300 osmoles
osmolality effects osmosis
what does iso-osmotic mean, give an example
same osmolality
e.g concentration of electrolytes outside the cell is equal to that inside the cell - no movement - no change in shape of cell
what is tonicity
ability of a solution to affect the cell - depends on concentration and permeability of the membrane to the solute
HYPOtonic - low
HYPERtomic - high
describe what happens to a cell in a hypotonic solution
low concentration of solutes that do not cross the membrane - high water content - dilute
therefore cell would absorb water from outside and swell
describe what happens to a cell in a hypertonic solution
high concentration of electrolytes outside the cell means low concentration of water
water moves to try and equal it out so cell would lose water and shrivel
what do baroreceptors measure
pressure
what do osmoreceptors measure
concentration
what are the 4 treatments for dehydration
1) fluid therapy
2) Gelofusine - plasma expander (high osmotic pressure can draw liquid from interstitial fluid into cells - EMERGENCY
3) 5% glucose solution - isotonic
4) 0.9% saline - isotonic e.g post op fluid loss
what factors influence water movement
hydrostatic pressure = the force exerted on the membrane by water/fluid
in a resting cell this will be stable as intracellular = interstitial
water will always follow what?
solutes
electrolytes move across plasma membrane by ? then water follows by ?
diffusion
osmosis
what is the most dominant extracelluar ion and what is its normal range
Sodium (Na+)
around 0.5g / 135-145 mmol/L
