Digestion and Absorption process of GI Flashcards
Where does digestion start and end
begins in the stomach and ends in small intestine
Where does absorption take place
small intestine
2 main paths of absorption
cellular and paracellular
Cellular absorption
lumen –> apical membrane –> intestinal epithelial cell –> basolateral membrane –> bloof
Where are the transporters for cellular absorption
in membrane
Paracellular absorption
intestinal epithelial cell –> lateral intercellular space –> intestinal epithelial cell
2 types of digestive activity
cavital (luminal) digestion and membrane (contact) digestion
Cavital digestion
digestion from action of enzymes of salivary glands, stomach and pancreas
Membrane digestion
hydrolysis by enzymes of epithelial cells
Folds of Kerckring
longitudinal folds of small intestine
Function of villi and microvilli in small intestine
increase surface area
Where are the villi the longest and where are they the shortest
longest in duodenum and shorter in terminal ileum
Site of activity of digestive enzymes
microvillar surface
Barrier that allows some passage of nutrients, water, electrolytes
microvillar surface
Enterocytes
epithelial cells of intestine
Function of enterocytes
digestion, absorption, and secretion
Goblet cells
mucus-secreting cells
Function of goblet cells
physical, chemical and immunological protection
Paneth cells function
mucosal defense against infection and bacteria
What controls the flux of solutes and fluid between lumen and blood
enterocyte membrane
4 ways enterocytes move solutes and fluid
pinocytosis, passive diffusion, facilitated diffusion, and active trasport
Where does pinocytosis occur and whats its function
base of microvilli and used for uptake of protein
What movement takes place during absoprtion
transmural
Monosaccharides are absorbed by
enterocytes
Three end products of carbohydrate digestion
glucose, galactose, and fructose
What does lactose break into
glucose and galactose
What does sucrose break into
glucose and fructose
What breaks down starch
alpha amylase
What can starch break into
maltose, dextrins, maltotriose
Transport mechanisms for absorption of carbs
co-transport and facilitated diffusion
GLUT 2
gets glucose, galactose and fructose from intracellular into blood
SGLT1
takes glucose and galactose out of the lumen into intracellular
GLUT5
takes fructose from lumen to intracellular
What kind of transport is SGLT 1
secondary active transport
Where is the Na/K ATPase located on the cells for carb absorption
basolateral side
Lactose intolerance
failure to digest carb
Why does lactose intolerance occur
brush-border lactase is lacking
Result of lactose intolerance
osmotic diarrhea– undigested lactose remains in lumen and holds water
What happens to unabsorbed and undigested lactose
ferments into methane and hydrogen gas causing excess gas
How are proteins digested to absorbable forms
proteases in stomach and small intestine
Stomach protease
pepsinogen –> pepsin
Small intestine proteases
trypsinogen –> trypsin, chymotrypsinogen –> chymotrypsin, proelastase –> elastase, proccarboxypeptidase (A or B) –> carboxypeptidase (A or B)
Endopeptidases
pepsin, trypsin, chymotrypsin, elastase
Exopeptidases
carboxypeptidase A and B
What does protein breakdown into in the stomach
amino acids and oligopeptides
What does protein breakdown into in the small intestine
amino acids –> dipeptides and tripeptides, oligopeptides –> amino acids –> dipeptides and tripeptides
Function of trypsin
catalyzes hydrolysis of trypsinogen (autocatalysis)