Osmosis
Osmosis
• When the diffusing substance is water,
and when the diffusion takes place
through a semi permeable membrane the
process is called osmosis.
• Also the movement of water down a
concentration gradient from an area of
high solvent concentration (weak solution)
to an area of low solvent concentration
(stronger solution.)
Osmosis
• Consider 2 salt solutions, (one dilute and the
other concentrated) separate by a semi
permeable membrane.
• The 2 solutions will tend to equalize in
concentration. i.e. the dilute one will tend to
become more concentrated whereas the
concentrated one will tend to become more
dilute they do this by for example a process
called osmosis.
• Diffusion is movement of substances from a
region of higher concentration to a region of
lower concentration.
Isotonic solutions.
• Two solutions with the same solute
concentrations are said to be isotonic
• The normal salt concentration of blood in the
body is approximately 0.9% NaCl.
• This is also known as physiologic saline.
• Therefore blood and physiologic saline solutions
are isotonic i.e. they have the same salt
concentration.
• Also a 5.5% glucose solution is isotonic with
body fluids.
Osmosis
• Suppose a Red blood cell were placed in a
small amount of physiologic saline? What
will happen?
Hypotonic solution
• A hypotonic solution is one that contains a lower
solute concentration than that of another
solution
• Distilled water and tap water are hypotonic
compared to blood.
• Suppose a red blood cell is placed in water
(hypotonic) the salt concentration of blood is
greater than that of water. Therefore osmosis
will take place.
• Water moves into the cells
• Leading to Hemolysis.
• Thus hypotonic solutions are not used for blood
transfusion.
Hypertonic solution
• Is one that contains a higher solute
concentration than that of another solution.
• For example 5% NaCl is an example of
hypertonic solution when compared with blood.
• Suppose a red blood cell is placed in a
hypertonic solution, what will happen ?
• It would shrink because water moves out of the
cell
• Saline cathartics such as magnesium sulfate,
milk of magnesia, and magnesium citrate are
absorbed slowly and incompletely.
• When ingested they form a hypertonic solution
and water moves out from tissue spaces.
Reverse osmosis
• When water and a salt solution are
separated by a semi permeable
membrane, If the pressure greater than
the osmotic pressure is applied to the salt
solution side of the membrane, the entire
process will be reversed
• This process is called Reverse Osmosis.
Osmosis
• This continues until the solution is isotonic
with body fluids.
• The additional water in large intestine
produces watery stool that is easily
evacuated.
Diffusion
• Also known as passive transport
• Is process whereby a substance moves
from an area of higher concentration to an
area of lower concentration.
• The greater the difference in concentration
the faster the rate of diffusion.
• No external source of energy is needed.
Diffusion
• Gases will diffuse into one another.
• When a bottle of ether is opened, the odor can
soon be detected from a distance
• Diffusion of gases takes place faster than
liquids.
• Another example is in loss of perspiration in the
body.
• Here the moisture flows from an area of high
concentration (skin) to one of lower
concentration (the air )
• The higher the moisture content of the air, the
slower the rate of evaporation of moisture from
the skin
Diffusion across the cell membrane
Factors affecting diffusion across a
plasma membrane.
• The greater the lipid solubility of the
diffusing particle the more permeable the
membrane will be.
• Smaller particles will generally diffuse
faster than large ones.
• O2, H20 and CO2 will rapidly diffuse
across the lipid bilayer
Facilitated diffusion.
• Allows diffusion of large , membrane –
insoluble compounds such as sugars,
amino acids.
• Is also a passive process.
• Substances bind to transport proteins
• Rate of movement depends on the
number of available transporter.
Facilitated diffusion