Cellular processes: glucose transport Flashcards
role of tight junctions
hold epithelial cells at luminal edges
- barrier restrict movement of substances
- can selectively allow ions into intercellular space
- fence: prevents the membrane proteins from diffusing in the plane of the bilayer
–> allows separation of epithelial cells into two distinct domains where proteins can be different in each domain
apical domain
(lumincal or mucosal) membrane that faces lumen of organ or body
basolateral domain
membrane that adheres to adjacent basement membrane and interfaces with blood
transcellular transport
transport via the cells accross two cell membranes
absorption: transport from lumen to blood
secretion: blood to lumen
rules:
- entry step for absorp. is apical, for secretion, it is basolateral
- electrochemical gradient: is entry or exit passive or active
- electroneutrality: movement of + or - ion will attract counter ion
- osmosis: net ion movement = osmolarity difference = water movement
paracellular transport
transport via the paracellular (intercellular space) only driven by the gradient set up by the movement of substances from trans cellular transport.
- determined by diffusion and junction tightness
epithelium funtion classifications
leaky - paracellular transport dominates because less tight junction strands
tight - more tight junction strands so more electrical resistance so transcellular dominates
epithelial mediation of absorption and secretion
in GI tract and kidney
proximal to distal, leaky to tight epithelium because absorption occurs early on.
glucose-galactose malabsorption syndrom
a mutation to the glucose symporter int he small intestine means that sugar is retained in the intestine lumen
- glucose come in but is not absorbed - increased osmolarity = water out of cells into lumen = diarrhoea (watery chyme)
glucosuria
glucose in urine
glucose symporter can’t absorb glucose fast enough during kidney filtering
