Tonicity
Tonicity
Passive transport are means by which
molecules move because of their own
Inherent energy. The movement is random.
This random movement eventually produces
an equal distribution of the molecules
throughout an environment.
Tonicity
Diffusion is one type of passive transport.
If an area has a higher concentration of
a substance, this substance tends to move
toward areas of lesser concentration of that
substance until an even distribution of the
substance is achieved.
Tonicity
Original photograph
A drop of food coloring
diffuses from an
area of high
concentration (the drop)
to the area of low
concentration ( the rest
of the container).
Examples in our bodies would include the
movement of glucose, oxygen, and ions.
Tonicity
The tendency to move to an area of lesser
concentration is a pressure or concentration
gradient. This is true in all fluids; gases and
liquids.
No energy is required to be added in order
for this movement to occur.
Tonicity
Osmosis is a special type of diffusion.
Osmosis is the diffusion of water through a
semi-permeable or selectively permeable
membrane. Water molecules are small
enough to pass through the pores of the
membrane but other larger molecules can
not pass through the membrane.
Tonicity
Our cell membranes are selectively
permeable membrane.
Osmosis follows the same pressure gradient
as do molecules during diffusion; they move
from an area of high water molecule
concentration to an area of lower water
molecule concentration. This is referred to as
osmotic pressure.
Tonicity
Solution Types:
• Isotonic – A solution that has the same
Amount of solute as the solution it is
compared to.
• Hypotonic – A solution that has a lesser
concentration of solute than the solution it is
compared to.
• Hypertonic – A solution that has a greater
concentration of solute than the solution it is
compared to.
Tonicity - Isotonic
Red Blood Cells in an isotonic
solution. The amount of solute
in the cells is equal to the solution.
Public Domain image
From WikiMedia Commons
Osmosis is taking place.
Water enters and exits the cells
at an equal rate. There is no net
gain in cell volume or mass.
Tonicity - Hypotonic
Red blood cells in a hypotonic
solution. The amount of solute
in the cells is more than the
solution (less solvent).
Public Domain image
From WikiMedia Commons
The solution has more water
than the cells, a pressure
gradient exists. Water moves
by osmosis into the cells. The
cells swell and may burst.
Tonicity - Hypertonic
Red blood cells in a hypertonic
solution. The amount of solute
in the cells is less than the
solution (more solvent).
Public Domain image
From WikiMedia Commons
The solution has less water
than the cells, a pressure
gradient exists. Water moves
by osmosis from the cells. The
cells shrink and may get a
scalloped looking border.
Tonicity
Remember these are comparative strengths
based upon the amount of solute.
•
ISO means the same
•
HYPO means below
•
HYPER means greater
Solutes “suck”. A greater amount of solute
“sucks” the water to it.
Tonicity
Diffusion and osmosis are important
processes to cells and to our bodies. These
processes are part of a group of processes
that help our bodies maintain homeostasis a
stable internal environment. The body has
many homeostatic processes. Diffusion and
osmosis form the foundation for many of
them.
Tonicity
Diffusion can be used by our bodies to
deliver and remove molecule to and from
our cells.
Osmosis helps us maintain fluid and
electrolyte balances in our cells.
Tonicity
In a medical situation you might require a
transfusion of saline solution because of
sudden blood volume loss. A saline
transfusion (0.9% NaCl) is isotonic.
If you are in medical care for an extended
time and require many transfused medicines
an isotonic saline can be used to periodically
flush and rinse the catheter that has been
inserted into a blood vessel