L23: Mucosal Digestion Flashcards
digestion breaks down complex nutrient molecules while absorption refers to the transport of simple molecules across the _______
intestinal epithelium
much of enzymatic digestion and all of the absorption takes place on?
the surface of intestinal epithelial cells
surface extension of the small intestine occurs at what 4 levels
- GI tract elongation
- plica circulares (mucosal folds)
- villi (epithelial projections)
- brush border (Microvilli on surface of villi)
what is the glycocalyx
apical membrane covered with glycoproteins of enterocytes
what is the mucosal barrier between the lumen and aprical membrane composed of
- microvilli/glycocalyx
- mucus
- water
what are the two phases of carbohydrate digestion
- luminal phase - enzymes from salivary glands and pancreas breakdown large polymeric molecules
- membranous phase - “brush border digestion” small polymers are broken down into monomeric molecules that can be asborbed. Enzymes are bound to the epithelium, are part of the glycocalyx
what is enteritis
distruction of the epithelial lining; villi are destroyed
what enzyme is in the oral cavity and hydrolyzes starch to smaller polysaccharides
alpha amylase
in the stomach, ___-___% of starches are converted to maltose
30-40
what are the forms of carbohydrates
- fiber (indigestible by mammals)
- sugars
- starches
- glycogen
bacterial hydrolases in the rumen/cecum/colon ferment fiber into __?
VFAs
T/F: fiber cannot be degraded by luminal or mucosal hydrolases in the small intestine
T
T/F: fiber remains in the lumen and provides bulk to the feces; helps in fluid retention and aids in passage
T
during the luminal phase of protein digestion, proteins are broken down into ?
peptides & amino acids
where does protein luminal phase digestion occur and via what enzymes
begins in stomach w/ gastric enzymes and HCl, is completed in duodenum by pancreatic enzymes
what is the membranous phase of protein digestion and whay enzymes are involved
further breakdown of amino acids
peptidases in the apical membrane of enterocytes
in protein digestion, luminal and membrane bound ______ facilitate the breakdown to di and tripeptides and amino acids
peptidases
what occurs during lipid digestion
triglycerides are hydrolyzed into monoglycerides and FFAs
what lipids can be found in the diet
- triglycerides (FAs, glycerol)
- cholesterol
- phospholipids
- lipid soluble vitamins A, D, E, K
fats are generally not water soluble whereas ______ enzymes are
lipolytic
primary vs secondary bile acids
primary bile acids (Cholic and chenodeozycholic acid) are synthesized by theliver
secondary bile acids are the result of bacterial actions in the colon
some bile acids are conjugated with _____ or _____ in the liver
taurine or glycine
what are micelles
small sized droplets containing FFA and bile acid
- act as lipid ‘shuttles’ and increase lipid solubility in chyme
what are the 4 steps of fat digestion in the SI
- emulsification by bile salts
- hydrolysis of triglycerides
- micelle formation
- micelle content absorbed in jejunum
carbohydrate digestion ends with … in the membranous phase
monomers (glucode, fructose, galactose)
protein digestion ends with…
di and tripeptides and amino acids
where is enterokinase located and what does it do
in the brush border, activates trypsin from trypsinogen
what enzyme is responsible for the inital minimal digestion of fat digestion in the oral cavity
lipase
where does fat emulsification occur
stomach and small intestine
the initial emulsification of fat in the stomach occurs with HCl, whereas the finalization of emulsification in the small intestine uses…
bile acids + phospholipids
insufficient synthesis and secretion of enzymes from 90% of pancreas
Exocrine pancreas insufficiency (EPI)
produced by epithelial cells in the glycocalyx in duodenum
