Tonicity

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Tonicity
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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.

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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.

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Tonicity
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).
Original photograph
Examples in our bodies would include the
movement of glucose, oxygen, and ions.
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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.

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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.

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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.

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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.

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Tonicity - Isotonic
Red Blood Cells in an isotonic solution. The
amount of solute in the cells is equal to the
solution. Osmosis is taking place. Water enters
and exits the cells at an equal rate. There is
no net gain in cell volume or mass.
Public Domain image From WikiMedia Commons
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Tonicity - Hypotonic
Red blood cells in a hypotonic solution. The
amount of solute in the cells is more than the
solution (less solvent). 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.
Public Domain image From WikiMedia Commons
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Tonicity - Hypertonic
Red blood cells in a hypertonic solution. The
amount of solute in the cells is less than the
solution (more solvent). 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.
Public Domain image From WikiMedia Commons
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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.

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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.

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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.

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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