Animal Physiology – Hoorcollege
College 1 Osmosis:
Water and ion exchange between a cell/organism and its environment mainly depends on
physicochemical processes and membrane properties.
- Diffusion and osmosis
- Water balance and ion regulation
The tonic properties of a solution are always related to the permeability of a plasma membrane
The excretory organs serve to regulate the internal environment
Three basic processes play a role in urine formation: ultrafiltration, reabsorption and excretion
The way an animal gets rid of its N-containing waste products depends on the amount of water it has
at its disposal for this process.
Osmoregulation (or hydromineral regulation) encompasses those processes that regulate the water-
and ion balance of an organism or cell.
The total concentration of osmotically active particles per litre water is expressed in Osmoles (osmol)
and is referred to as osmolarity
- Osmoles per kg water is referred to as osmolality
Osmotical ‘problems’ are directly related to the ion concentrations outside (environment) and inside
(bodily fluids) of the animal or cell. → there is only a problem when there is a difference between
inside and outside, when there is no difference there is no need for the animal to reflux (because
there is no flux of water or ions).
- We therefore always speak of osmotic gradients.
Diffusion= random movement of particles as result of their thermal energy (temperature).
𝛥𝐶
Diffusion can be measured with Fick’s law: J = D ×
𝑋
- J= the net diffusion speed (amount per unit of time)
- ΔC= the concentration gradient across distance X
- D= diffusion coefficient (includes features like permeability of the membrane and particle
Mw)
- ΔC ≠ 0 → net diffusion.
o In this case there is a difference
between left and right. Then if you
remove the distributor, you will get a
net diffusion, and ΔC = 0 .
o Left and right concentration is the same, so therefore no net diffusion.
- Cell in a solvent (water), the cell has a dissolved
substance and the cell floats in the water. And
the membrane of the cell has a semipermeable
membrane, which is permeable for the water
and impermeable for the substance (particles).
o There is a concentration difference, so
water is going inside the cell. Because
there are more particles inside the cell than outside the cell. Water goes inside the
cell, to equalize this concentration difference.
o As a result this cell will swell and if the cell cannot swell as much as it should be, then
the cell will burst. And this is the first reason why an animal should osmoregulate.
o Hemolysis → red blood cell burst → in a hypotonic condition
- Or if the extracellular fluid becomes hyperosmotic → there are more dissolved particles
outside the cell, the water inside the cell will go out and the cell will shrink.
, o Under the microscope you see this with red blood cells in hypertonic condition, the
red cells will shrink.
- If there is no difference in concentration → there is no problem for the animal, and there will
be no change with the environment.
Now there is inside the cell a small capillary. There are particles inside the cell, so water will be
attracted inside the cell, but now water can go inside this capillary. Then you can measure the
pressure you need to counteract (tegenwerken) this process. Because you can push back the water.
- with van ‘t Hoff measure this pressure
o π = R × T × (n/V)
▪ π= osmotic pressure (Pa = N/m2)
▪ R= gas constant → 8.314 J/mol/K
▪ T= temperature in Kelvin
▪ (n/V)= number of particles (mol) per unit of volume (m3) → concentration of
the solute.
o The osmotic pressure is essentially the osmotic difference in pressure relative to the
surrounding solution.
o What is π for a solution of 39 g
glucose per litre?
o Pressure of water is 0, because
no particles in the water.
An osmotic gradient contains energy. Via
freshwater and seawater the difference between
these two, you can pressure and with this
pressure you get energy. But to make freshwater
from seawater is an energy-demanding process.
- π is determined by the concentration, but not the kind of dissolved substance.
Two solutions are isosmotic when they exert a similar osmotic pressure.
- So when they contain equal concentrations of osmotically active particles.
A solution is isotonic relative to a cell when that cell does not change its volume in the solution.
- Tonicity is, therefore, defined based on the response of cell in solution.
Isosmotic is not synonymous to isotonic.
- The 0.5 mol/l will divide itself in the blue one. Because the cell is permeable for urea.
- First compartment A is isosmotic relative to compartment B → the total concentration of A
(1) and B (1) is the same.
- When the urea is divided, the A is hypotonic relative to B → A has less particles (0.75) than B
(1.15). →water will move from A to B
- In the green side also urea will divide.
- A is hyperosmotic, because there are in total the most particles (1) compared to B (0.5).
- After urea is divided → isotonic, because in A and B both are 0.75 of urea.
, So osmolarity is the total concentration (activity) of osmotically active particles (n/V)
Tonicity is the part of the osmotic pressure caused by particles to which the cell membrane is
impermeable.
Seawater= 1000 mOsmol.
Fresh water= <20 mOsmol. → it can be 0.0 or below 20
Why do animals have to osmoregulate → why is hypertonicity a bad thing?
- Hypotonicity is ofcourse bad, because then the cells will burst and explode.
- Consequences of hypertonicity:
o Decrease in cell volume
o Increase in ion strength (cytoplasm becomes more concentrated)
▪ Then more consequences
• Macromolecular crowding; → proteins, DNA/RNA
cannot function as they should.
o Aggregation and accumulation
• Disruption of protein
function
o Folding errors
**** consequences of hypertonicity
When a cell is moved into a more-dilute solution, it initially
swell with water. The cell must reduce its content of dissolved entities to restore its original volume.
When a cell is moved into a more-concentrated solution, it initially loses water and shrinks. The cell
must increase its content of dissolved entities to restore its original volume.
Different Animals use different molecules to regulate their cell volume.
If a cell is placed from 300 mOsm (physiological
state where most cells are in) to a higher
concentration of solution then that cell will make
particles, in general it will make organic molecules
(amino acids/ureum/glycerol/TMAO). And it is the
other way round, placing in less mOsm, then the
cell will make less organic molecules.
College 1 Osmosis:
Water and ion exchange between a cell/organism and its environment mainly depends on
physicochemical processes and membrane properties.
- Diffusion and osmosis
- Water balance and ion regulation
The tonic properties of a solution are always related to the permeability of a plasma membrane
The excretory organs serve to regulate the internal environment
Three basic processes play a role in urine formation: ultrafiltration, reabsorption and excretion
The way an animal gets rid of its N-containing waste products depends on the amount of water it has
at its disposal for this process.
Osmoregulation (or hydromineral regulation) encompasses those processes that regulate the water-
and ion balance of an organism or cell.
The total concentration of osmotically active particles per litre water is expressed in Osmoles (osmol)
and is referred to as osmolarity
- Osmoles per kg water is referred to as osmolality
Osmotical ‘problems’ are directly related to the ion concentrations outside (environment) and inside
(bodily fluids) of the animal or cell. → there is only a problem when there is a difference between
inside and outside, when there is no difference there is no need for the animal to reflux (because
there is no flux of water or ions).
- We therefore always speak of osmotic gradients.
Diffusion= random movement of particles as result of their thermal energy (temperature).
𝛥𝐶
Diffusion can be measured with Fick’s law: J = D ×
𝑋
- J= the net diffusion speed (amount per unit of time)
- ΔC= the concentration gradient across distance X
- D= diffusion coefficient (includes features like permeability of the membrane and particle
Mw)
- ΔC ≠ 0 → net diffusion.
o In this case there is a difference
between left and right. Then if you
remove the distributor, you will get a
net diffusion, and ΔC = 0 .
o Left and right concentration is the same, so therefore no net diffusion.
- Cell in a solvent (water), the cell has a dissolved
substance and the cell floats in the water. And
the membrane of the cell has a semipermeable
membrane, which is permeable for the water
and impermeable for the substance (particles).
o There is a concentration difference, so
water is going inside the cell. Because
there are more particles inside the cell than outside the cell. Water goes inside the
cell, to equalize this concentration difference.
o As a result this cell will swell and if the cell cannot swell as much as it should be, then
the cell will burst. And this is the first reason why an animal should osmoregulate.
o Hemolysis → red blood cell burst → in a hypotonic condition
- Or if the extracellular fluid becomes hyperosmotic → there are more dissolved particles
outside the cell, the water inside the cell will go out and the cell will shrink.
, o Under the microscope you see this with red blood cells in hypertonic condition, the
red cells will shrink.
- If there is no difference in concentration → there is no problem for the animal, and there will
be no change with the environment.
Now there is inside the cell a small capillary. There are particles inside the cell, so water will be
attracted inside the cell, but now water can go inside this capillary. Then you can measure the
pressure you need to counteract (tegenwerken) this process. Because you can push back the water.
- with van ‘t Hoff measure this pressure
o π = R × T × (n/V)
▪ π= osmotic pressure (Pa = N/m2)
▪ R= gas constant → 8.314 J/mol/K
▪ T= temperature in Kelvin
▪ (n/V)= number of particles (mol) per unit of volume (m3) → concentration of
the solute.
o The osmotic pressure is essentially the osmotic difference in pressure relative to the
surrounding solution.
o What is π for a solution of 39 g
glucose per litre?
o Pressure of water is 0, because
no particles in the water.
An osmotic gradient contains energy. Via
freshwater and seawater the difference between
these two, you can pressure and with this
pressure you get energy. But to make freshwater
from seawater is an energy-demanding process.
- π is determined by the concentration, but not the kind of dissolved substance.
Two solutions are isosmotic when they exert a similar osmotic pressure.
- So when they contain equal concentrations of osmotically active particles.
A solution is isotonic relative to a cell when that cell does not change its volume in the solution.
- Tonicity is, therefore, defined based on the response of cell in solution.
Isosmotic is not synonymous to isotonic.
- The 0.5 mol/l will divide itself in the blue one. Because the cell is permeable for urea.
- First compartment A is isosmotic relative to compartment B → the total concentration of A
(1) and B (1) is the same.
- When the urea is divided, the A is hypotonic relative to B → A has less particles (0.75) than B
(1.15). →water will move from A to B
- In the green side also urea will divide.
- A is hyperosmotic, because there are in total the most particles (1) compared to B (0.5).
- After urea is divided → isotonic, because in A and B both are 0.75 of urea.
, So osmolarity is the total concentration (activity) of osmotically active particles (n/V)
Tonicity is the part of the osmotic pressure caused by particles to which the cell membrane is
impermeable.
Seawater= 1000 mOsmol.
Fresh water= <20 mOsmol. → it can be 0.0 or below 20
Why do animals have to osmoregulate → why is hypertonicity a bad thing?
- Hypotonicity is ofcourse bad, because then the cells will burst and explode.
- Consequences of hypertonicity:
o Decrease in cell volume
o Increase in ion strength (cytoplasm becomes more concentrated)
▪ Then more consequences
• Macromolecular crowding; → proteins, DNA/RNA
cannot function as they should.
o Aggregation and accumulation
• Disruption of protein
function
o Folding errors
**** consequences of hypertonicity
When a cell is moved into a more-dilute solution, it initially
swell with water. The cell must reduce its content of dissolved entities to restore its original volume.
When a cell is moved into a more-concentrated solution, it initially loses water and shrinks. The cell
must increase its content of dissolved entities to restore its original volume.
Different Animals use different molecules to regulate their cell volume.
If a cell is placed from 300 mOsm (physiological
state where most cells are in) to a higher
concentration of solution then that cell will make
particles, in general it will make organic molecules
(amino acids/ureum/glycerol/TMAO). And it is the
other way round, placing in less mOsm, then the
cell will make less organic molecules.
