Solute Exchange Flashcards
function of cell membrane (5)
Semi-permeable – allow movement of water
Provide support and protection
Cell-to-cell recognition – e.g. immune system
Controls what enters or leaves the cell – e.g. ion movement in nerves
Regulates cell function – e.g. Insulin-mediated glucose uptake
describe phospholipid bi-layer
where does it form bi-layer?
which part is polar and non-plar? where?
Consists of two layers of amphipathic phospholipids
Phosphate head is polar (hydrophilic) - outer
Fatty acid tails is non-polar (hydrophobic) - inner
Form bilayers in solution
describe capillaries
diameter?
link to arterioles?
thickness?
permeability?
where? (2) higher density where?
Capillaries: Smallest diameter blood vessels Extension of inner lining of arterioles Endothelium only – 1 cell thick Semi-permeable
Vessels that connect terminal arterioles to venules
Found near every cell in the body but higher density in highly active tissue (muscles, liver, heart, kidneys and brain)
exchange at capillaries
what are the two different exchanges?
how do they take place? and what is exchanged at the different exchnages?
Solute exchange (passive diffusion, filtration) : O2, glucose, amino acids, hormones, drugs
Fluid exchange (flow down pressure gradients) : regulation of plasma and interstitial fluid volumes
passive transport
relation to gradient?
energy?
example of molecules?
Movement of molecules DOWN a gradient
Concentration / Pressure / Osmosis
Does Not require energy
Simple (O2/CO2) or facilitated (ions, glucose)
active transport
relation to gradient?
energy?
example?
Movement of molecules AGAINST a gradient Requires energy (uses ATP) e.g. ATP-dependent pumps, endocytosis, exocytosis
4 passive transport processes
type of gradient? example?
1) DIFFUSION
Concentration gradient
e. g. O2 uptake from lungs into blood
2) CONVECTION
Pressure gradient
e. g. Circulation
3) OSMOSIS
Osmotic pressure (water) gradient
e. g. water uptake by cells
4) ELECTROCHEMICAL FLUX
Electrical and Concentration gradient
e. g. ion flow during an action potential in a nerve
What controls the rate of solute transport? (3)
Properties of passive diffusion
Properties of solutes and membranes (Fick’s law)
Properties of capillaries
Ultimately
Together these parameters form the concept of permeability
Properties of passive diffusion (3)
what is it great for?
Does not require energy (no ATP)
Molecules move randomly
Move from area of high to low concentration
Great for transport of lipid-soluble solutes very short distances, e.g. O2, CO2
why is passive trasnport effective only for short distances?
time taken for a molecule to move net distance equation?
Time taken (t) for one randomly moving molecule to move a net distance (x) in one specific direction increases with the distance squared
t = x2 / 2D
D = diffusion coefficient for molecule within the medium e.g. D for O2 in water vs. O2 in air are different
properties of solute affecting transport (3)
Concentration gradient
Size of the solute
Lipid solubility of solute (lipophilic, lipophobic nature)
properties of membrane affecting transport (4)
Membrane thickness/composition
Aqueous pores in the membrane
Carrier-mediated transport
Active transport mechanisms
Properties of solutes and membranes (Fick’s law)
eqaution?
what are the 4 factors?
- How much of a substance is transported per time? -
Solute movement - mass per unit time m/t (Js)
determined by 4 factors
Js = - D A Conc grad / x
D = Diffusion coefficient of solute – ease through solvent
A = Area
DC / x = Concentration gradient (C1-C2) across distance x
negative value : flowing ‘down’ a concentration gradient
3 types of capillairies
how does permeabilty change?
continous capillaries
fenestrated capillaries
discontinous capillaries
(more permeable from continous to discontinous hence more leaky)
continous capillaries
describe permeability and structure (2)
example where?
Moderate permeability
Tight gaps between neighbouring cells
Constant basement membrane
e.g. blood-brain barrier
