Gradients (all about the SOLUTE)

The plasma membrane of a cell lets water pass freely. Water will flow toward the side that has the most dissolved molecules (called solutes). Said another way, water will flow from a hypotonic solution toward a hypertonic solution until both sides of the membrane reach equilibrium.

a HYPERTONIC solution has more solutes than cell cytosol (H2O flows OUT of cell)

- cytoplasm of the cell has a lower solute concentration than the extracellular medium

a HYPOTONIC solution has less solutes than cell cytosol (H2O flows INTO the cell)

- cytoplasm of the cell has a higher solute concentration than the extracellular medium

- too much inflow, cell my lyse

- “Kaplan Exclusive!”: Look how the O in hypotonic looks like a SWOLLEN cell!

an ISOTONIC solution has the same solute concentration on both sides.

If a cell is in a Hypertonic solution, the cell will shrink.

If a cell is in a Hypotonic solution, the cell will expand.

If the cell is in an Isotonic solution, the cell will remain the same.

If the cell is Hypertonic with respect to the medium, it will expand, this infers that the solution it is in, the medium, is Hypotonic.

If the cell is Hypotonic with respect to the medium, it will contract(shrink), this infers that the solution it is in, the medium, is Hypertonic.

Good student-Doc thread on urine hypertonicity relative to blood: http://forums.studentdoctor.net/archive/index.php/t-833556.html