Digestion Lecture Flashcards
Cell types in the small intestine
enterocytes
respon. for digestion, absorption, secretion
turnover rate 3-6 days
susceptible to irradiation and chemotherapy
Cell types in the small intestine
goblet cells
mucous secreting
produce physical, chemical and immunological barrier
Cell types in the small intestine
patneth cells
part of defense, secrete agents that destroy bacteria
forms of enterocyte membrane control
pinocytosis (at base of microvilli)
passive diffusion
active diffusion
facilitated diffusion
transporters on the apical membrane of the enterocyte designed for taking in monosaccharides via _____transport
SGLT 1 is a Glucose-Na cotransporter, Galactose-Na cotransporter; uses secondary transport (duh)
GLUT2 is a fructose transporter
transporters on the basolateral membrane of the enterocyte designed for taking in monosaccharides via _____transport
Glut2, it takes in everything (glucose, galactose, fructose)
where is lactase located
on the brush boarder. deficiency causes osmotic diarrhea
undigested lactose is fermented into methane and hydrogen gas, causing excess flatulence
Stomach: protein digesting enzymes
“endopeptidases”
pepsin, typsin, chymotrypsin, elastase
“endopeptidases”
degrade peptides from interior peptide bonds
Stomach: protein digesting enzymes
“exopeptidases”
carboxypeptidase A
carboxypeptidase B
degrade peptides beginning at C terminus
Trypsinogen
converted to trypsin by ENTEROpeptidase
trypsin converts the ENDOpeptidases into their active form
what are the inactive/active form of the endopeptidases?
trypsinogen—> trypsin
chymotrypsinogen –> chymotrypsin
Proelastase —> elastase
Pro-carboxypeptidase A and B –> A and B carboxypeptidase
where are proteases actives?
in the stomach AND the SI
autocatalysis
trypsin’s conversion of trypsinogen into trypsin
pancreatic enzymes digest one another
Protein in the stomach is digested to ___ by ____
amino acids and oligopeptides by pepsin
protein in the small intestines is digested to ______ by ______
amino acids, dipeptides, tripeptides, oligopeptides
oligopeptides are further degraded by peptidase on the brush border to amino acids, dipeptides and tripeptides
Amino acid transporters in the small intestine in the apical membrane
secondary a.a.-Na cotransporter
there are four: one for acidic a.a., neutral a.a., imino a.a.s, basic a.a’s
dipeptides/tripeptides have an H-Di/Tri cotransporter as well
Amino acid transporters in the small intestine in the basolateral surface
four transporters for each group of amino acids using facilitated diffusion
internally there’s a peptidase to degrade dipeptides and tripeptides to a.a.s
dipeptides and tripeptides can diffuse out of the cell
pancreatic preteases
trypsin, chymotrypsin, elastase, caeboxypeptidase A and carboxypeptidase B
after degrading proteins, what happens to pancreatic enzymes?
they degrade one another and are reabsorbed
cystinuria
defect or absence of Na-amino acid cotransporters
transporter for di-basic amino acids (cystine, lysine, arginine, and ornithine) are absent from small intestine and kidney
genetic disorder
amino acids are secreted into feces
Hartnup Disease
Cannot absorb neutral amino acids e.g. tryptophan
recessive genetic disorder
symptoms resemble those cause by pellagra
deficiency of niacin)
symptoms: diarrhea, mood changes, neurologic problems, res scaly skin photosensitivity short stature uncoordinated movements
urine has high concentration of neutral amino acids
Cystic fibrosis transporter mutations
associated with deficiency of amino acid transporters
CFTR transporter in the apical region of duct cells in pancreas
CFTR secretes chlorine, which moves back into the cell down a gradient, and pushing HCO3 into the duct lumen
CFTR mutations decrease bicarbonate secretion
pH elevation prevents activated trypsin from catalyzing the trypsinogen to trypsin conversion
ability to flush active enzymes from the duct may be lost
result– acute or recurrent peancreatits
Where are lipids digested?
in the stomach and small intestine
Triglycerides are digested via 3 enzymes
lingual lipase, gastric and prancreatic lipase
cholesterol esters are degrade by one important enzyme
cholesterol esterase hydrolase
phospholipids are degraded by
phospholipase A2
phospholipid —> lysolecithin-FA
what must occur initially for lipid digestion
solubilized, formed into micelles by bile and transported to the apical region of the enterocytes
pancreatic lipase
cholesterol ester hydrolase, phospholipase A2, and pancreatic lipase
