Membrane Transport Flashcards
(29 cards)
Total Body Water of a 70kg human and the divisions
TBW = 42L
Plasma = 3 L
Interstitial = 13 L
Intracellular = 25L (majority)
Relative concentrations of Na+, K+ and Cl- across membrane
Na+ has greater EXTRACELLULAR conc, gradient leads in
K+ has greater INTRACELLULAR conc, gradient leads out
Cl- has greater EXTRACELLULAR conc, gradient leads in
what is the fraction of blood made up of red cells called
hematocrit
what does the concentration gradient of charged particles lead to
an electrochemical gradient
why do plasma proteins affect solute distribution between plasma and interstitial fluid
because of the volume they occupy and the charge they carry
what are the 5 ways in which small molecules can cross cell membranes
passive diffusion
aqueous diffusion
facilitated diffusion
active transport
endocytosis
what type of molecules can pass directly through a membrane by passive diffusion
lipophilic molecules (e.g. steroids)
what type of proteins form aqueous pores that facilitate diffusion
aquaporins
passive vs aqueous diffusion
passive does not require a vehicle
aqueous is a molecules that cannot pass through the membrane but their conc gradient allows them to enter the cell
what causes the conformational change in facilitated diffusion
chemical reaction (binding) between molecule and carrier protein
why doesn’t facilitated diffusion require energy
net 0 change in energy because the conformational change causes a downhill movement down a concentration gradient
what are the two types of active transport
primary active transport: hydrolysis of ATP
secondary active transport:
coupling movement of an uphill movement to a downhill movement
what determines the flux of a given charged solute
the electrochemical potential energy difference
which two types of transport are subject to Michaelis - Menten kinetics
facilitated diffusion and active transport as they involve a finite number of proteins so can be saturated and plateau
how to determine the electrochemical potential energy difference for a molecule carrying a charge
chemical potential energy difference + electrical potential energy difference
what determines the driving force of a charged solute across a membrane
electrochemical potential energy difference
when is flux 0
in a state of equilibrium (at equilibrium potential / Ek)
how to calculate the Ex of an ion
61.5log10[X]o/[X]i
how to calculate the driving force of a charged particle
(membrane voltage) - Ex
positive is outward and negative is inward
what is the equilibrium potential of a charged particle
potential at which there is not net movement of a given ion
when to use Fick’s Law
to determine the flux of an electrically neutral solute
how does the pKa and local pH affect the pharmacology of a drug
pKa = pH at which 50% of drug is ionised
unionised form can permeate the membrane
If a drug is ionised it will carry a hydration shell and be prevented from crossing the membrane
what are the principal sites of carrier mediated transport
blood brain barrier
gastrointestinal tract
placenta
renal tubule
biliary tract
what is the blood brain barrier
protective barrier of endothelial cells and capillaries which must be crossed to enter the brain. Prevents toxins entering the CNS
