Water Transport and Osmosis Flashcards
water mass in body
- 60% of total body weight
- 70kg-42 liters of water
- ICF is 2/3 of that-28 L, 40%
- ECF is 1/3- 14 L, 20%
ICF maintenance
- osmosis
- optimal concentration of solutes means optional function of cells
ECF distribution
- extravascular- 75 % of ECF- 11L
- intravascular- 7% of body weight- 5L (25% of ECF (plasma))
intravascular distribution
- hematocrit
- 55% blood volume is plasma (3L)
- 45 % cellular (2L)
- plasma is 25% of ECF
movement of water across membrane
- facilitated diffusion through aquaporins-RBC and kidney, aqueous humor in eye and CSF in brain
- fluid exchange in lung and formation of bile
- formation of interstitial fluid in all muscle
- can be unmediated too
osmosis
- process of net movement of water caused by a concentration difference between two compartments
- goes to a side with a higher concentration of solute (higher osmolarity)
- particle numbers, not size
- high water chemical potential means low osmolarity
osmotic pressure
- amount of pressure that would have to be applied to force water back to its original chamber
- DF of water from chemical gradient (in lower Osm compartment)
- hydrostatic pressure developed in right compartment that is equal and opposite DF and leads to no net movement of water is equal to the osmotic pressure difference between the solutions
hydrostatic pressure
- force of gravity down on water molecules
- hydrostatic pressure gradient from gravity opposes the DF from the chemical gradient of water in the low Osm compartment
osmotic pressure 2
- water will flow from lower osm to higher in a U tube until solute concentrations is almost equal and the hydrostatic pressure formed by the rising water opposes the remaining osmotic pressure
- magnitude of osmotic pressure is related to solute concentration
- osmotic pressure higher in more concentrated solutions
- difference in osmotic pressure is a DF- drives water from low osm to high osm
edema
-increase hydrostatic- intra to extra
or decrease osmotic- blocks intra to extra
low osmotic pressure
- lower osmolarity
- higher water concentration
high osmotic pressure
- higher osmolarity
- lower water concentration
osmosis goes from
- lower osmotic pressure to higher osmotic pressure
- because gradient is a DF and gradient goes from high to low, so water goes the other way
- higher osmotic pressure on one side pulls water to that side
isotonicity
- same osmolarity
- nothing happens to cell
hypotonicity
- lower osmolarity outside cell
- water comes into the cell
hypertonicity
- higher osmolarity outside the cell
- water leaves the cell
add water to plasma
- increase ECF volume
- decreases ECF osm
- water moves into ICF and increases ICF volume and decreases osm
add isotonic solution to plasma
- increases ECF volume without changing osm
- no effect on ICF volume and osm
adding hypertonic saline to plasma
- increases ECF osm
- water leaves ICF into ECF
- decreases ICF volume and increases ICF osm
- increases ECF volume
response to cell shrinking
- cell is normal 300 osm/ so is plasma
- plasma osm to 450- water out of cell
- now both osm are 450 but cell lost volume
- activates two ion transporters which bring ions into cell, osm increases in cell
- water follows the ions in
- volume restored but osm not
sweat
100 osm
- Na and Cl diffuse back and just water leaves
- ECF osm increases
- water flows from cells and cellular volume decreases and osmolarity increases-which then can pull more water back
- we also have other mechanisms like thrist
response to cell swelling
- osm normal 300
- plasma drops to 200 osm
- water comes into cell
- ion transporters put ions out of cell
- water follows
- volume restored but osm remains 200
movement of fluid during dehydration
- sweat comes from blood
- fluid drawn from blood (plasma) to form sweat
- fluid lose by the blood leads to loss by rest of ECF (ECF osm increases)
- ECF osm draws water from ICF
- cell volume decreases and triggers water retention by kidneys