Physiology - GI Flashcards
What do gastric secretions contain?
HCl, pepsin, mucous, water
What does water do to bolus
turns it into chyme
liquidy consistency
What are the 3 structures that make up the SI?
duodenum, jejunum and ileum
What is digestion?
conversion of complex dietary substances to a form that can be absorbed
What are the 2 commonly digestive processes in the SI, and which enzymes is it mediated by?
luminal - pancreatic enzymes secreted into duodenum
membrane - enzymes situated at the brish border of epithelial cells
What are enterocytes?
Type of epithelial cells that lines the inner surface of the SI
- have microvilli on their surface + imp role in absorption of nutrients
Absorption
process by which absorbabl products of digestion are transferred across apical + basolateral membranes of enterocytes
General mechanism of digestion + absorption
What requires no breakdown in digestion
glucose
Eg of molecule that undergoes luminal hydrolysis of polymer to monomer
proteins –> AA
Eg of molecule that undergoesbrushborder hydrolysis
oligomer to monomer
Eg of molecule that undergoes** intracellular hydrolysis**
peptide breaksdown to AA intracellularly
Eg of molecule that undergoes luminal hydrolysis + intracellular resynthesis
triacylglycerol -> glycerol + fatty acids -> triacylglycerol
properties of amylose
- polysaccharide
- straight chain
- a-1,4 linkages
properties of amylopectin
- polysacccharide
- branched
- a-1,4 and a-1,6 linkages
properties of glycogen
- polysaccharide
- brandched
- a-1,4 and a-1,6 linkages
linkage in sucrose
glucose + fructose a-1,2 linkage
linkage in lactose
glucose + galactose b-1,4 linkage
Where is a amylase produced?
salivary glands + pancreas
What is the role of alpha amylase?
- break down of internal alpha 1,4 linkages but not terminal alpha 1,4 linkages
What can alpha amylase not cleave?
- cannot cleave alpha 1,6 linkages at branch points in amylopectin or 1,4 linkages adjacent to branch points
What are the products of alpha amylase?
linear glucose oligomers (maltotriose + maltose) and alpha limit dextrins
Oligosaccharides are __________ proteins with a ____ domain that faces the ____ of the GI tract
integral membrane, catalytic, lumen
What linkage is cleaved by oligosaccharidases in maltose, maltoriose and alpha limit dextrins to yield glucose
alpha 1,4 linkages
What degrades the alpha 1,4 linkages in straight chain oligomers (up to 9 monomers in length)?
maltase
role of sucrase
hydrolyses sucrose to glucose and fructose
role of isomaltase
only enzyme that splits the branching of a-1,6 linkages of alpha limit dextrins
glucose and galactose absorbed by what transportoe?
SGLT1 - secondary active transport mediated
fructose is absorbed by what?
GLUT5 - via facilitated diffusion
exit of all monosaccharides is mediated by what?
facilitated diffusion - GLUT2
What criteria’s must be met for substrate to be transported via SGLT1?
- hexose in d conformation
- one that can form a pyranose ring
What is the mode of operation of SGLT1?
In general, pepsin cleaves what to what
proteins into peptides
not imp for protein digestion
is pepsin an endo- or exopeptidase?
endo
What are the 5 pancreatic proteases?
- elastase (endo) –> oligopeptides
- trypsin (endo) –> oligopeptides
- chymotrypsin (endo) –> oligopeptides
- carboxypeptidase A (exo) –> single AA
- carboxypeptidase B (exo) –> single AA
brush border peptidases
numerous, have affinity for larger oligopeptides, either endo/ exopeptidases
cytoplasmic peptidases primarily hydrolyse what?
dipeptides + tripeptides
