13 + 14 Flashcards
13. Van’t Hoff`s law and the medical significance of osmotic pressure. Thermodiffusion, heat-transfer, general description of transport processes (Onsager`s linear relationships). 14. Transport across membranes: permeability coefficient and its dependence on material properties. Passive and active transport, facilitated diffusion.
What is osmosis?
The unidirectional matters flow, which takes place by means of diffusion
→ the phenomenon where solvent particles diffuse as a result of a concentration gradient. They will diffuse from an area of lower concentration to an area of higher concentration through a semipermeable membrane.
What is osmosis equilibrium?
Dynamic equilibrium is reached when the same amount of solvent diffuse into the bag and effluxes from it as a consequence of pressure difference
What is osmotic pressure?
the minimum pressure which needs to be applied to a solution to prevent the inward flow of its pure solvent across a semipermeable membrane
This is a model-experiment of the determination of osmotic pressure
→ Look at the model and describe what is going on (focus on c)
Due to the semipermeable membrane
- all the red molecules stay in compartment I
- black molecules reach a uniform distribution as a result of diffusion → They have equal amounts in both compartments
→ By using ideal gas law, we can determine the pressure in both compartments (remember, compartment I also contains red molecules beside black one)
→ Pressure difference between these compartments is the osmotic pressure
What is Van’t Hoff Law?
- The van’t Hoff theory describes that substances in dilute solution observe the ideal gas laws, resulting in the osmotic pressure.
c is the concentration of solute
R is the universal gas constant
T is the absolute temperature
Does Van’t Hoff Law apply for solutions with strong electrolytes?
NO
When will the osmotic phenomenon occur?
When there are solutions of different concentrations on the 2 sides of semi-permeable barrier
What is equilibrium pressure?
It is given by the difference between osmotic pressures of the 2 solutions of different nonpermiable solvents (cannot pas through) the barrier on the 2 sides
What is osmolarity?
“osmotic concentration” refers to the amount of solute particles per liter solvent (taking into consideration the number of dissociated ions if applicable.)
What are isotonic solutions?
The solutions in which osmotic pressure is equal in 2 different solutions
Examples of isotonic solutions with respect to mammalian cytoplasm
Solutions of 3.8% sodium citrate, 5.5% glucose, 0.15M (0.87%) NaCl solutions
Why is NaCl solutions a physiological solutions?
What is haemolysis?
- The rupture of red blood cells
Describe haemodialysis
- Treatment of patients with severe kidney disease
- Relies on osmotic phenomenon
By application of an “artificial kidney” instrument
→ The blood circulation is connected to cellophane-coil
→ blood is made to flow through it and then re-enters the vein of patient
→ The water-soluble metabolic compounds (protein-products, waste,…) exit the blood by osmosis (together with water), while essential plasma-proteins (albumin, globulin, etc.) and cellular elements of blood remain within
What is thermodiffusion?
- Diffusion that occurs due to a temperature gradient.
Based on the image below, describe the model of thermodiffusion and then give the expression for this.
- A container of volume V is filled with gas (particles with uniform mass) and divided by a wall along x axis
→ At start points, densities (n) on the 2 sides are equal
→ The temperature is higher on the left side than the right side
→ The speed of particles is higher on the left side than right side
→ More fast particles will cross the wall than slow one
What is Onsager-relation?
- A unified form of the laws of transport processes
- J = LX
- J - flux density
- L - Thermodynamic force exerted by the gradient of the corresponding intensive quantity
- L - conductive coefficient
Examples of laws describing different transports
- Fourier
- Ohm
- Fick
- Hagen Poiseuille
3 types of transport of substances across membranes
- Passive diffusion
- Facilitated diffusion
- Active transport
Which transport processes are considered as as passive transport
- Diffusion
- Facilitated diffusion (with the help of channel or carrier protein)
What is permeability coefficient?
- It its proportional to the ratio of diffusion coefficient to the total thickness of membrane bilayer
- It characterizes the transport across membrane
- Unit is m/s
Which molecules can cross the membrane by means of diffusion?
- Hydrophobic molecules such as O2 and N2
- Some small polar molecules such as H2O, urea, glycerine and CO2 molecules
Describe passive transport processes
materials can move according to the concentration gradient, its flux depends on the size, shape, and polarity of the molecule as well as on the temperature (gases, steroids, alcohol, water)
Describe active transport
materials move against concentration gradient, either utilizing directly the energy of ATP (primary active transport), or utilizing a chemical gradient built up by a primary transporter (secondary active transport), this can be further classified as symport or antiport
Describe facilitated diffusion
- Utilizing a carrier protein
- Binding site has access both on extracellular and on the intracellular sides
- At a given concentration gradient, the transport velocity is higher in the case of facilitated diffusion
- Follows Michaelis-Mentes kinetics, saturable and can be selectively inhibited
What are ion channels?
multisubunit transmembrane proteins, selective for given ions, their open/closed states are governed either by regulatory molecules (e.g. neurotransmitters, hormones) or by change in membrane potential
Comparison of transporters
