Flashcards in Digestion and Absorption Deck (74)
What is digestion?
The process by which ingested food is broken down chemically into absorbable molecules.
What is absorption?
Is the movement of nutrients, water and electrolytes from the lumen of the intestine into blood.
What are the 2 pathways of absorption?
Cellular path - the substances enter the intestinal epithelial cells via the apical (luminal
membrane) and are extruded via basolateral membrane to enter blood.
Paracellular path - substances move across the tight junctions, through the lateral interspaces into blood.
What must carbohydrates be digested to in order to be absorbed?
What are the monosaccharides that can be absorbed?
Fructose, Galactose and Glucose
What is amylose?
It is the straight chain polymer
What is amylopectin?
It is the branched chain polymer
What does trehalose break down to?
What does sucrose break down to?
1 Glucose 1 Fructose
What does lactose break down to?
1 Glucose 1 Galactose
Why can't cellulose be broken down?
It has beta-1,4 linkages which cannot be broken down in humans due to the lack of the enzyme
What is the function of the enzyme alpha-amylase?
Cleaves the α-1,4 linkages in carbohydrates
What is the result of digestion with pancreatic amylase?
It yields a mix of disaccharides, trisaccharides
What further digests the saccharides after the amylase does?
These disaccharides are further digested to monosaccharides by intestinal brush border enzymes:
- α-dextrinase (isomaltase)
What is unique about α-limit dextrins?
Alpha-dextrins have the α-1,6 linkage that
can only be broken with alpha-dextrinase
What is the function of SGLT1?
SGLT1 transports glucose and galactose against their concentration gradients by coupling their transport to that of Na+ (active process).
What is the function of GLUT5?
Transports fructose across the apical membrane and it does not require an Na+ ion
What is the function of GLUT2?
It transports glucose, galactose and fructose across the basolateral membrane
What is the function of sucrase?
What is the function of lactase?
What is lactose intolerance and what are symptoms of it?
Lack or deficiency of lactase in the brush border- lactose is not digested to glucose and galactose. If lactose is ingested (in milk or milk products), lactose remains undigested and unabsorbed in the intestinal lumen – and retains water causing osmotic diarrhea.
What is congenital lactose intolerance?
It is a lack of jejunal lactase and is much rarer than normal lactose intolerance. It can be dangerous so replacement with a sucrose/fructose diet may be necessary
What is glucose-galactose malabsorption?
It is due to a mutation in SGLT1 and a fructose diet is recommended
What enzyme starts protein digestion in the stomach?
What are endopeptidases?
They hydrolyze the interior peptide bonds of proteins
Example – pepsin, trypsin, chymotrypsin, elastase.
What are exopeptidases?
They hydrolyze one amino acid at a time from the C-terminal ends of proteins and peptides
Example - carboxypeptidases A&B.
What activates trypsinogen?
Enterokinase. It will then become trypsin and activate the other proteases.
Is pepsin in the stomach essential for protein digestion?
Pepsin is not essential for normal protein digestion, since in people whose stomach has been removed or who d not secrete gastric H+, have normal protein digestion and absorption.
Where does the major protein digestion occur?
In the small intestine with the pancreatic enzymes