VI- Digestion and Absorption Flashcards
where Ca absorbed at
duodenum only
where iron absorbed at
duodenum only
where carbs absorbed at
duodenum and jejunum
where fats absorbed at
entire small intestine
where protein absorbed at
entire small intestine
where bile salts absorbed at
terminal ileum only
where vit B12 absorbed at
terminal ileum only
carb digestion pathway
- polysaccharides digested by a-amylase @ lumen of intestine
- oligosaccharides dig by carb-ases @ brush border
- monosaccharides dig/transported by SGLT1 and GLUT5 @ brush border
substrates of SGLT1
- glucose
- galactose
coupled to sodium
substrate of GLUT5
fructose
substrates of GLUT2
all 3 monosaccharides
-glucose, galactose, fructose
protein digestion pathway
- protein from diet dig by pepsin @lumen of the stomach
- oligopeptides and amino acids dig by trypsin @lumen of intestine + peptidase @brush border
- absorbed as oligos and AAs
amino acid absorption mechanism
nutrient-sodium coupled transporter
-highly functional during fed state
oligopeptide absorption mechanism
- transport across membrane by H+ linked cotransporters like PEPT1
- further dig to AAs by intracellular peptidases
lipid digestion pathway
- lipids aka triglycerides and cholesterol get emulsified @lumen of stomach
- FFAs, cholesterol, tri/diglycerides more emulsified with bile + pancreatic lipase + co-lipase @ lumen of duodenum
effects of CCK
- gallbladder for contraction by Ach
- pancrease for acinar secretion
- stomach for reduced emptying
- sphincter of oddi to relax by Ach
all lead to protein, carb, lipid digestion
emulsification process
emulsion lipid droplet reduced in size by lipases and bile acids until micelle formed
colipase function
required for activation of pancreatic lipase
-anchors lipase to emulsion droplets
fat soluble vitamins
vit A, D, E, K
also partition into micelles with lipids
B12 absorption
- B12-IF through intestine
- IF receptors in ileum uptake to blood
- B12-transcobalamin through blood to liver
methods of iron uptake
- heme associated endocytosis
- transferrin receptor mediated
- divalent cation transporter 1 DCT1
all require ferrous form of iron
how iron is reduced
low pH in stomach OR associated with vitamin C OR reductase at brush border
calcium absorption mechansim
thru Ca channel on duodenum apical membrane
-requires vit D for transcription
lactose intolerance
an absorption disorder so def in lactase = lactose in lumen broken down by bacteria instead so gas and cramping/bloating
-unabsorbed lactose in lumen causes water retention = diarrhea
