Physiology 1 Flashcards
what is osmolarity
the concentration of osmotically active particles present in a solution
how do you calculate osmolarity in the body
concentration of a solution x the number of osmotically active particles present
what is the osmolarity of body fluids
300mosmol/l
what is tonicity
the effect a solution has on cell volume
what is an isotonic solution
one that causes no change in cell volume
what is a hypotonic solution
one that causes an increase in cell volume
Water moved from the solution into the cell
what is a hypertonic solution
one that causes a decrease in cell volume
(cell looses fluid by osmosis from inside to outside cell0
what is a fluid with an osmolarity <300
hypotonic
has less osmotically active particles in it than inside the cell so water moves into the cell
what is a fluid with osmolarity >300
hypertonic
more osmotically active particles are outside the cell than in so water leaves the cell via osmosis
why is the permeability of the cell membrane important in osmosis
because some cell membranes favour one solution over another
eg. urea and sucrose both have an osmolarity of 300 (so should be isotonic) however sucrose is isotonic and urea is hypotonic
this is because RBC membranes are v permeable for urea but not as much for glucose
what are the 2 main body compartments which hold water
intracellular fluid (2/3)
extracellular fluid (1/3)
what is the extracellular fluid made up of
interstitial fluid (80%)
plasma (20%)
lymph + trans cellular fluid (CSF,pleural) (negligible)
how do you measure the volume of fluid in a specific compartment
tracers
measure the distributed volume of a specific tracer in a body compartment
what tracer measures plasma volume
labelled albumin
what tracer measures total body water
3H3O
what fluid outputs does the body have no control over (insensible)
skin - diffusion of water across skin surface area
lungs - see it on cold day when you breath out vapour
what fluid outputs does the body control (sensible loss)
sweat
urine
faeces
eg. if dehydrated you can reduce amount of urine produced and if over hydrated you increase the amount of urine produced
what are the fluid inputs to the body
fluid intake
food intake
metabolism
how is water imbalance manifested (differences between water input and output)
osmolarity
why do you still produce urine (a concentrated urine) when you are v dehydrated
some metabolites being excreted need to be excreted in fluid
what ions are most abundant in the intercellular fluid
K+
what ions are most abundant in the extracellular fluid
Na+
CL_
HCO3-
(like the sea)
osmolarity of ECF and ICF are the same true/false
TRUE
if there are changes in salt conc in extracellular fluid it changes osmolarity causes water to move to try and restore the change - balances out
what are fluid shifts
movement of water between ICF and ECF in response to an osmotic gradient
maintain homeostasis
what are some challenges to homeostasis
gain or loss of water
gain or loss of NaCl
gain or loss of isotonic fluid (bc it changes ECF volume)
when does electrolyte balance occur
when rates of electrolyte gain = loss
do electrolyte concentration affect water balance?
YES
via changes in osmolarity
what are the two major contributors to the osmotic concentrations of ECF and ICF (electrolytes)
K+
Na+
what is the relationship between sodium and water
WATER FOLLOWS SALT
Why is it so vital to regulate Na
it is mainly present in the ECF so is a MAJOR determinant of ECF volume and therefore blood volume/pressure
where is 95% of the body’s k+
In the cells (intracellular fluid)
what can happen if there are small leakages or increased uptake of potassium into cell/out of cells
muscle weakness- paralysis
cardiac irregularities
