Block 2 Lecture 17 Flashcards
(28 cards)
what are the two sides to a plasma membrane
basolateral and apical
where is the basolateral side located
the blood side of the layer and is exposed to ISF
where is the apical side located
outside of the body such as the lumen of intestines)
what is an exception to the apical side of the membrane
choroid plexus where the apical side is exposed to the cerebrospinal fluid
what are the principle barrier epithelia that line organs that have large surfaces exposed
GI tract, kidney nephron, and liver (other significant are choroid plexus, retina and exocrine glands)
what are the 2 types of pathways for transport
paracellular = between adjacent cells transcellular = across individual cells
what happens in paracellular transport
molecules move through tight junctions
what are tight junctions
a complex of proteins that attach cells to one another
what are the functions of tight junctions
- ) barrier that reduces free diffusive movement of molecules via the paracellular pathway.
- ) provides a barrier to prevent mixing of molecules between basolateral and apical membranes
where are tight junctions located in between cells
typically closer to the apical side
what size molecules can pass through tight junctions
any molecule less than 4A (glucose is slightly larger)
what do claudins do
establish the permselective character of tight junctions and form aqueous pores of about 4A
claudins that form pores that contain a surplus of cationic residues in the postulated pore forming region have been found to favor the paracellular movement of what?
anions such as Cl-
claudins that form pores that contain a surplus of anionic residues in the postulated pore forming region have been found to favor the paracellular movement of what?
cations such as Na+
what are zymogens released by in the pancreas?
secretagogues
what are the 4 types of secretagogues
CCK, ACh, VIP, and secretin (CCK and ACh most important)
how do CCK and ACh work
by binding to the G protein coupled CCK receptor or the muscarinic ACh receptor which activates protein kinase C (PKC) producing an increase in intracellular Ca2+
how does VIP and secretin work
they bind to different receptors that stimulate PKA to release zymogens
what “help” zymogen granule release (SSC)
SNARE proteins, Rab proteins, and synaptotagmin
what do SNARE proteins do
there are more than 60 SNARE proteins expressed in cells to get right vesicles to fuse in right place. there are v-SNARES and t-SNARES
what do Rab proteins do
they are small G proteins the bind and hydrolyze GTP that help assemble SNARE fusion complex. there are about 70 Rabs which aid in targeting specificity
what are synaptotagmins proteins and what do they do
they are integral membrane proteins in vesicle membranes. they bind Ca2+ and once activated can stimulate the fusion event in exocytosis. 15 synaptotagmins involved in vesicle fusion in different cell types
why is SSC energetically unfavorable
because when vesicle membranes and plasma membrane get close to each other they repel because they are both negatively charged
what happens in acinar cells of the exocrine pancreas
- ) driven by Na,K ATPase in basolateral membrane
- ) Na+ gradient drives accumulation of Cl- from blood into acinar cells via Na,K, 2Cl cotransporter
- ) Cl- moves from acinar cells into lumen through apical Cl- channel because of inside negative membrane potential
- ) trans epithelial secretion of Na+ relies on paracellular pathway. Cl- moving into lumen makes it negative providing electrical force to support paracellular diffusion of Na+ through tight junction
- ) increase in NaCl in lumen supports osmotically driven flux of water via aquaporins
