intro to epithelial transport Flashcards
two categories of epithelia based on function
absorptive and secretory
cardinal properties of epithelia
ability to translocate ions
asymmetry underlying the capacity for sectoral transport of ions, water and solutes
two surfaces of epithelia named
apical- facing lumen
basolateral- facing interstitium
how are the two faces separated?
tight junctions
importance of tight junctions
prevent paracellular transport, only enable transcellular
two types of epithelia
tight and leaky
tight epithelia explained
more selective, as solutes cannot move between cells
expression of transporters in membrane determine the absorptive activities of the epithelia, under close hormonal regulation
where are tight epithelia mainly found?
distally, such as the collecting duct, colon. found towards the end of the kidney tubules and GI tract
leaky epithelia explained
tight junctions have a less complex structure, forming an imperfect seal with a low resistance leak pathway for ions and water, a shunt pathway
relatively non-selective and allows bulk handling of isosmotic solutions
found proximally, proximal tubule of the renal tubule and GI tract
benefits of this balance of leaky and tight epithelia
unable initial bulk absorption followed by hormonally controlled selective absorption to adjust the composition of fluids
paracellular pathway defined
movement of molecules between cells, depending upon osmotic and hydrostatic and electrochemical gradients
transcellular pathway defined
through cells, depending on active transport
what happens when charged ions move across an epithelium?
charge separation, enabling a potential difference to be measured
what does the orientation of the PD depend upon?
which ions move and in which direction
the magnitude of the PD?
depends upon how easy it is for the ions to pass, therefore whether it is leaky or not
