MR 2 Membrane Permeability Flashcards Preview

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Flashcards in MR 2 Membrane Permeability Deck (37):

What kinds of molecules can pass through membranes?

hydrophobic and small, uncharged, polar molecules


What kinds of molecules cannot pass through membranes?

Large, uncharged, polar molecules and ions


What is passive diffusion?

Dependent on permeability and concentration, rate of passive transport increasing linearly with increasing concentration gradient


What is faciliatated diffusion?

Where permeability of membrane for a substance increased by incorporation of a specific protein in the bilayer. Models include carrier molecules(ping-pong) and protein channels.


What is active transport?

Transport of ions or molecules against concentration and or electrical gradient, requiring energy from the hydrolysis of ATP


What type of free energy change do active processes have?



What are co-transporters?

Transporters that transport more than one molecule?


What is a uniport?

transports 1 molecule in 1 direction


What is a symport?

Transports more than one molecule in the same direction


What is an antiport?

Transports more than one molecule in opposite directions


What are the extra and intracellular Na+ concentrations?

outside- 145mM inside- 12mM


What are the extra and intracellular K+ concentrations?

outside- 4mM inside- 155mM


What are the extra and intracellular Ca2+ concentrations?

outside-1.5mM inside 10-7M= 0.1um


What are the extra and intracellular Cl- concentrations?

outside- 123mM inside- 4.2mM


What does Na+/K+ ATPase do?

antiport using energy from ATP to move 2K+ into the cell and 3Na+ out of the cell to form Na+ and K+ gradients necessary for electrical excitability and to drive secondary active transport


For what processes does the sodium potassium pump drive secondary active transport?

pH control regulation of cell volume Na+ absorption in epithelia Nutrient uptake e.g glucose from small intestine


What are K+ channels mainly responsible for?

Diffusion down conc grad set up by the sodium potassium pump, K+ moving out of cell, is mainly responsible for the resting membrane potential of -70mv


What does Plasma Membrane Ca2+-ATPase(PMCA) do?

Uses ATP to expel residual Ca2+ from the cell in exchange for H+ (antiport). high affinity, low capacity


What does Sarco(endo)plasmic Reticulum Ca2+-ATPase(SERCA) do?

Accumulates Ca2+ into SR/ER in exchange for H+ using ATP (antiport) High affinity, low capacity


What is secondary active transport?

Facilitated diffusion using a concentration gradient set up by an active transport process


What does the sodium calcium exchanger (NCX) do?

Expels 1 Ca2+ in exchange for 3Na+(antiport) via secondary active transport using the Na+ gradient set up by the sodium potassium pump. Responsible for removing most Ca2+. Activity is membrane potential dependent


Is NCX electrogenic?

Yes, current flows in direction of Na+ gradient


What happens in ischaemia relating to NCX?

ATP depleted Sodium potassium pump therefore inhibited Na+ accumulates in cell leading to depolarisation NCX reverses Na+ moves out and Ca2+ moves in High Ca2+ is toxic


What happens to CFTR in diarrhoea?

In gut epithelial cells its activated by protein kinase A, it pumps out more Cl- into the lumen causing water to follow causing diarrhoea


What are the acid extruders in cell pH control?

Na+/H+ exchanger (NHE) Na+ dependent Cl-/HCO3- exchanger (NBC- sodium bicarbonate cotransporter) note: uses Na+ grad


What is the alkali extruder?

Cl-/HCO3- exchanger (AE-anion exchanger) (Band 3)


What transporters cause alkali influx?

NBC Na+/HCO3- co transporter (symport)


How is cell volume regulated?

Transport of osmotically active ions e.g Na+, K+, Cl- or organic osmolytes (amino acids) in and out of cell causing water to follow


What are the mechanisms to resist cell swelling?

A image thumb

What are the mechanisms to resist cell shrinking?

A image thumb

Outline bicarbonate resorption by the proximal tubule

A image thumb

What transporter do loop diuretics block and where is this in the kidney?


thick ascending limb


What transporter to thiazides block and where in the kidney does this occur?

NCCT Na+/Cl- co-transporter

distal convoluted tubule


What protein does amiloride block and where in the kidney does this occur?

Epithelial sodium channel

distal convoluted tubule


Why do you get hypertension in hyperaldosteronism?

aldosterone stimulates the reuptake of ions in the cortical collecting duct by binding with glucocorticoid receptors so too many ions are taken back


How does spironolactone act?

glucocorticoid receptor antagonist blocking aldosterone from activating receptors in the cortical collecting duct and so reducing ion reuptake and hypertension.


What transporters raise intracellular Ca2+

Facilitated diffusion:

Receptor operated Ca2+ channels (ROC)

Voltage operated/gated Ca2+ channels (VOCC/VGCC)

IP3 gated Ca2+ channels

Ca2+ induced Ca2+ release (CICR)

Store operated Ca2+ channels (SOC)

Mitochondrial Ca2+ uniporters

Secondary active transport: NCX in reverse in depolarised cells