intro Flashcards
epithelia function as a barrier
the epithelia separates the lumen from the basement membrane and the basolateral membrane
- stops things moving and mixing of body compartments
- allows selective movement across
what are epithelial cells joined by
junctional complexes - creates selective barrier
paracellular transport
substances can move between the cells
- utilise the junctional complexes
transcellular transport
move through the cell
transport through tight epithelia with tight junctions
no paracellular route
- restricted transport
- e.g. stomach, colon and kidney collecting duct
transport through leaky epithelia
high rate of transport including a paracellular route
- e.g. small intestine and kidney proximal tubule
what are Claudins
claudins are proteins in junctional complexes that allow for junction permeability
- type of claudin can affect what the junction allows through
main junctional proteins
occludins and claudins
subtypes of claudins
1 = tight (tight epithelia)
2 = monovalent cations (leaky)
10a = anions (kidney)
10b = cations (kidney)
16 = Mg 2+, Ca2+ (kidney)
barrier function of junctional complexes
mechanical integrity of epithelium
fence function of junctional complexes
maintaining polarity by separating apical and basolateral membranes
transcellular transport direction
unidirectional
- absorption and secretion
- substrate must cross 2 membranes
lipid transport
simple diffusion
water soluble substances transport
e.g. sugars, amino acids, ions
- carrier (protein) - mediated transport
what do all cells have
all cells have high potassium, low sodium and a negative Vm
- all cells express pumps, carriers and channels
