S1: How Molecules Move Around the Body - Passive Transport Flashcards
What two mechanisms transport molecules around the body?
Passive
Active
What is Passive Transport?
- Movement of molecules down a gradient
- Does not require energy
What is Active Transport?
- Movement of molecules against a gradient
- Requires energy (uses ATP)
List the four passive transport processes
Diffusion
Convection
Osmosis
Electrochemical flux
What is diffusion?
It is molecules going down their concentration gradient
e.g. O2 uptake from the lungs
What is convection?
It is molecules going down a pressure gradient
e.g. Blood flow from heart to blood vessels
What is osmosis?
Water going down concentration(pressure) gradient
e.g. Water uptake by cells
What is electrochemical flux?
Electrical and concentration gradient
e.g. Action potential in nerve
What is the equation for rate of transport?
Rate of transport (J) = Energy difference / Resistance to transport (R)
What is Darcy’s Law on blood flow?
Blood Flow = Pressure difference between arteries and veins/ Resistance produced by blood vessels
What is Brownian motion?
The random, un-directional thermal motion of molecules - in diffusion
List some properties of diffusion
- Brownian Motion
- No input from any other force
- Each molecules has a different properties
- Thermal Motion: Molecular Motion depends on absolution temperature (measured in kelvin)
What is absolute zero and how does this affect diffusion?
Absolute zero is 0K or 273 degrees.
At this temperature there is no kinetic motion
How fast is diffusion (equation)?
The time taken (t) for one randomly moving molecules to move a net distance (x) in one specific direction increases with the distance squared (x^2)
D= diffusion coefficient for molecule within the medium e.g. O2 in the water vs O2 in air
t=x^2/(2D)
How does distance affect rate of diffusion?
Speed of diffusion decreases with increasing distance
How is diffusion clinically important?
- Useful for transporting molecules over very short distances - Diffusion is very and an effective transport process on a cellular scale (nm and um)
- Not useful at transporting molecules over distances > mm - Diffusion is very slow at transporting molecules around the body
- Oxygen transport
- Limitations exposed in a heart attack - Infarcted area of cardiac muscle due to lack of O2 supply
What is Fick’s Law (Js)?
- Processing controlling diffusion
- ‘Steady state diffusion down a constant concentration gradient’
- Units: m/t(Js)
Js=-Concentration gradient x area(A) x diffusion coefficient of solute(D)/distance (x)
Concentration gradient= concentration difference/distance
What are the 4 factors of Fick’s law optimised in the body?
D= Solute size (small solutes diffuse faster)
A= Capillary density (areas of diffusion have high capillary and recruitment)
X= Distance between capillary and cell where diffusion is important is very small e.g. alveoli
Change in concentration changes according to metabolic activity
Why is Fick’s law negative?
Molecules move down a concentration gradient
What is D?
How does diffusion coefficient (D) change with different molecules?
D is greater for small molecules
D is smaller for large molecules
D is the ease of which a molecule moves through a solvent
How do different solutes diffuse through the cell membrane?
Lipid soluble solutes: Diffuses across all cell membrane and is rapid
Lipid insoluble solutes:
- It diffuses across a slow pore area via aqueous pores (gaps through capillary walls). It is slow.
- Enter via specific protein carriers in the membrane where they enter by facilitated diffusion until the carriers become saturated.
Give examples of lipid soluble solutes
Oxygen
Carbon Dioxide
Anaesthetics
Glycerol
Give examples of lipid insoluble solutes
Electrolytes (NaCl) Glucose Amino Acids Plasma Proteins Most therapeutic drugs
Give an example of a lipid soluble solute entering aqueous pores
Na+ through ion channel
Give an example of a lipid soluble solute entering protein carrier
Glucose in brain
Why can some molecules diffuse faster across the cell membrane?
The ability of a molecule to cross a membrane relates to its permeability.
