Absorption Flashcards
What are the roles of crypt and villi in the small intestine?
Crypts- secretion
Villi- Absorption
What part of the small intestine absorbs?
Villi
What part of the small intestine secretes?
Crypts
What happens to glucose at the small intestine?
Absorbed without digestion by the villous epithelial cells into the bloodstream
What happens to sucrose at the small intestine?
Brush-border hydrolysis of oligomer to monomers glucose and fructose before being Absorbed by the villous epithelial cells into the bloodstream
What happens to proteins at the small intestine?
Luminal hydrolysis of polymer to monomer amino acid then Absorbed by the villous epithelial cells into the bloodstream
What is an oligomer
a molecule with a small number of monomers unlike a polymer which has large number of monomers
What are the only sugars allowed to be absorbed by villous epithelial cells?
Glucose
Fructose
Galactose
What enzyme breaks down sucrose?
Sucrase
What is sucrose broken down into?
Fructose
Glucose
What happens to peptides at the small intestine?
Absorbed into villous epithelial cell
Intracellular hydrolysis into amino acids before being absorbed into the bloodstream
What happens to peptides at the small intestine?
Luminal hydrolysis into mono-glyceride and fatty acids followed by intracellular resynthesis into triglyceride an then absorbed into lacteals of the lymphatic system
What is the difference between peptide and protein?
peptide is 2-50 amino acids
Protein is more than 50 amino acids
How is starch converted into simple sugars
alpha- amylase begins the process of carbohydrate digestion into maltose maltotriose and alpha-limit dextrins
These are further converted by maltase lactase and sucrase-isomaltase into one or both glucose and fructose
What is carbohydrate- starch initially digested into?
maltose maltotriose and alpha-limit dextrins
What is sucrase-isomaltase
two enzyme complex
Where are maltase lactase and sucrase-isomaltase located?
embedded in the apical membrane of the villous epithelial cells
What does maltase convert?
Maltose
Maltotriose
What is maltose broken down into?
Two glucoses
What converts alpha-limit dextrins
isomaltase of the sucrase-isomaltase
What is alpha-limit dextrins broken down into?
maltose maltotriose
What is lactose broken down into?
Galctose and glucose
What maltotriose broken down into?
Three glucoses
How is glucose absorbed by the bloodstream (process)
going to be transported across the apical membrane of the villous epithelial cell by transporter SGLT1 using the sodium concentration gradient across the cell membrane set up by the action of the sodium potassium ATPase
sodium moves down a favorable electrochemical gradient bringing glucose into the cell
Transported across basolateral membrane by GLUT2 facilitated diffusion
What is SGLT1
Na+-coupled glucose transporter
What is GLUT 2
Glucose transporter 2- facilitated diffusion
How is galactose absorbed by the bloodstream (process)
going to be transported across the apical membrane of the villous epithelial cell by transporter SGLT1 using the sodium concentration gradient across the cell membrane set up by the action of the sodium potassium ATPase
sodium moves down a favorable electrochemical gradient bringing galactose into the cell
Transported across basolateral membrane by GLUT2 facilitated diffusion
How is fructose absorbed by the bloodstream (process)
going to be transported across the apical membrane of the villous epithelial cell via transporter GLUT5 by facilitated diffusion
Transported across basolateral membrane by GLUT2
What is GLUT 5
Glucose transporter 5 - facilitated diffusion pathway
What transporter does glucose use to travel across apical membrane of the villous epithelial cells?
SGLT1
What transporter does galactose use to travel across apical membrane of the villous epithelial cells?
SGLT1
What transporter does fructose use to travel across apical membrane of the villous epithelial cells?
GLUT2
From most to least what parts of the small intestine carry out sugar absorption
duodenum> jejunum» ileum
How amino acids go across apical membrane(Digestion and Absorption of Proteins)
Seven mechanism
Some sodium dependant
sodium independent
How dipeptides and tripeptides go across apical membrane(Digestion and Absorption of Proteins)
Coupled to protons to travel across apical membrane via a symporter (cotransporter)
Protons are moving down a favorable gradient across the apical membrane
As proton comes in so does peptide
Digestion and Absorption of Proteins (mechanisms of breaking down protein)
Proteins by proteases are converted into sections of amino acids e.g (dipeptide, amino acids,etc)
Either travel across apical membrane in specific mechanism
Or longer peptides broken down at apical membrane to produce amino acids and then transported
Ways of digesting and absobing proteins(Digestion and Absorption of Proteins)
Luminal enzymes (proteases) digest proteins to amino acids before absorption by villus epithelial cells.
Luminal enzymes digest proteins to peptides, but enzymes in the apical membrane (brush border enzymes) of villus epithelial cells digest the peptides to amino acids before absorption by villus epithelial cells.
Luminal enzymes digest proteins to peptides, which are absorbed by villus epithelial cells and then digested within the cell (intracellular enzymes) to amino acids.
Digestion and Absorption of Proteins- Source of H+ ions
Sodium proton exchanger exploit the sodium concentration gradient setup by the sodium potassium ATPase
secondary active transport
acidifies unstirred layer on the apical lumen facing membrane of the villus epithelial cells
What type of transporter is sodium proton exchanger?
Antiporter
What is secondary active transport?
. Secondary active transport uses the energy stored in these gradients to move other substances against their own gradients.
How amino acids go across basal lateral membrane(Digestion and Absorption of Proteins)
3 sodium independant mechanisms
From most to least what parts of the small intestine carry out amino acid and peptide absorption?
duodenum> jejunum» ileum
What form are fats in when they are being digested and absorbed?
triglycerides
Digestion and Absorption of Fats
Triglyceride first converted to emulsion droplets by bile salts Become smaller droplets Pancreatic lipase breaks down into fatty acid and monoglyceride Combined with phospholipid and cholesterol into bile salt micelle Transported into unstirred layer next to brush border partly by diffusion, partly by the non propulsive movements within the small intestine Diffusion of fatty acids and monoglyceride (phospholipids and cholesterol) out of bile micelle cross into the apical lumen facing membrane within the villous epithelial cells within the smooth endoplasmic reticulum resynthesis of fat within chylomicron Chylomicron formation(emuslion droplets)
What does production of emulsion droplets depend on>
heavily on mechanical activity within the gastrointestinal tract
when and why are emulsion droplets made smaller?
Increase the surface area so that lipase can work on it
Happens in stomach and small intestine when churning up
Where can lipase work?
between lipid environment of the emotion droplet and the aqueous environment of the small intestine so needs emulsion droplets not raw triglyceride
cross the basal lateral membrane by exocytosis
delivered into the central lacteal
What do triglycerides break down into
Fatty acids
Monoglyceride
What does fatty acid and monoglyceride with phospholipids and cholesterol make?
Bile salt micelle
What is a bile salt micelle
Combination of
phospholipids, cholesterol
fatty acid and monoglyceride
Where do phospholipids and cholesterol involved in digestion of fats come from ?
liver
How is chylomicron formed?
With phospholipids and cholesterol
What is emulsion?
Emulsion is a key preliminary step reducing size of lipid droplets and increasing greatly the oil-water interface
From most to least what parts of the small intestine carry out amino acid and peptide absorption?
jejunum>duodenum»_space; ileum
