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absorption of metabolites in the intestines (absorption of electrolytes…
absorption of metabolites in the intestines
cellular transportation
passive
(down the molecule's/item's concentration gradient)
diffusion
osmosis
simple
carrier-mediated (facilitated)
active
(against the molecule's/item's concentration gradient)
vesicular
endocytosis (includes receptor-mediated, pinocytosis, and phagocytosis)
exocytosis
carrier-mediated
nutrients are absorbed (brought back to blood) via movement from
GI lumen to the apical epithelial cell surface
, through the epithelial cell, and
exiting through its basal surface to capillary or lacteal
absorption of a carbohydrate
a Na+/K+ pump
(active = requires ATP)
establishes a Na+ gradient (with low Na+ inside the enterocyte)
then
glucose is able to enter the apical side with Na+
(secondary active transport)
fructose is able to enter the enterocyte via facilitated diffusion
absorption of proteins
a Na+/K+ pump on the basal surface of the enterocyte (
active transport)
establishes a Na+ gradient
then
amino acids enter the apical surface with Na+ (
secondary active transport)
dipeptides and tripeptides enter the apical surface with H+ (these are broken down into amino acids in the enterocyte)
absorption of lipids
breakdown products of lipids enter the enterocyte via simple diffusion through the plasma membrane and exit the basal surface to the lacteal
absorption of electrolytes
ileum
basolateral:
Cl- transporter
apical:
Cl-/HCO3- exchange
colon
apical:
Na+ (absorption) and K+ (secretion) channels
aldosterone increases Na+ abs. and K+ sec.
basolateral:
Na+/K+ ATPase
jejunum
(major site for Na+/water absorption)
apical:
Na+ dependent coupled transporters (glucose, amino acid, H+)
basolateral:
Na+/K+ ATPase and HCO3- transporter