Water Transport/ Osmosis Flashcards
What accounts for most of the mass of the cell, and the human body?
Water accounts for 60% of body weight.
Where are the two places that water resides in the human body?
intracellular and extracellular
How is ICF volume maintained?
It is maintained within narrow limits by solute transport mechanisms that drive water into, or out of, the cell via osmosis
What two compartments is extracellular fluid volume distributed to?
intravascular and extravascular
How is ECF volume maintained? Why is maintenance so important?
It is regulate within normal limits by balancing the excretion of water by the kidneys to match the consumption of water.
This is essential for blood pressure regulation
How is water transported across the membrane?
Simple diffusion and by specific channels called Aquaporins (facilitated diffusion)
What is the definition of osmosis?
the net movement of H20 by a concentration difference of water between two compartments
Water moves “down” its concentration gradient (usually via aquaporins)
Is H20 more likely to flow to an area of low osmolarity or high osmolarity?
To an area of high osmolarity because high osmolarity indicates high solute concentration.
What is the main factor driving the net diffusion of water accross a semipermeable membrane?
solute and water concentration gradients
What is osmotic pressure?
It is the amount of pressure that would have to be applied to force water back into its original chamber before osmosis occurred to equillibrate the two chabers
What is hydrostatic pressure?
Pressure due to the force of gravity that is generated when water flows from one chamber to the next in order to equillibrate the chambers
(see page 73 of notes for picture)
What opposes hydrostatic pressure gradient in the vascular compartment?
The hydrostatic pressure gradient that drives fluid from the vascular compartment is opposed by the osmotic pressure gradient that results from the presence of impermeable protein solutes in the plasma
What causes edema?
the imbalance of the opposing forces (hydrostatic pressure and osmotic pressure).
What is the osmolarity of plasma in human blood?
300mOsm/L
What is ICF contribution to Total Body Weight?
40%
What is the ECF contribution to Total Body Weight?
20%
What is isotonicity?
ECF and ICF osmolarity both equal 300mOs/L.
No concentration gradient exists, and therefore there is no net movement of water.
What is hypotonicity?
When ICF osmolarity > ECF osmolarity.
There is more solute inside the cell and water enters the cell in order to equillibrate the two compartments
What occurs to cells in a hypotonic solution?
They swell due to the influx of water and can lyse.
What is hypertonicity?
When ICF osmolarity < ECF osmolarity.
There is more solute outside the cell and water leaves the cell in order to equillibrate the two compartments.
What occurs to cells in a hypertonic solution?
They shrink due to the efflux of water and can crenate.
Explain the response to cell shrinking:
- An increase in extracellular osmolarity sets up a gradient
- The cell shrinks as water leaves the cell
- Shrinkage activates two ion transporters and ions enter the cell.
- Via osmosis, water enters the cell and returns omolarity to normal (ICF=ECF)
Explain the response to cell swelling:
- A decrease in extracellular osmolarity sets up a gradient
- The cell swells as water enters the cell
- Swelling activates two ion transporters and ions leave the cell
- Via osmosis, water exits the cell and returns omolarity to normal (ICF=ECF)
Are the transporters activated during cell shrinkage response the same as the transporters activated during the cell swelling response the same?
No, they are different ion transporters
