PSC1002/L29 Stomach Flashcards
Give 3 functions of the small intestine.
Digestion
Nutrient absorption
Electrolyte absorption
Water absorption
Secretion
Which enzyme is involved in luminal digestion of starch-type polysaccharides?
Amylases
Which enzymes are involved in membrane digestion by disaccharidases? (3)
Maltase
Sucrase-isomaltase
Lactase
Why is amylase described as an endo-enzyme?
It can only break internal bonds so cannot produce monosaccharides
Give 2 transporters of the apical membrane.
SGLT1
Glucose, galactose
Na+ coupled, secondary active transport
Give a transporter of the basolateral membrane.
GLUT2
Facilitated diffusion
Give 3 types of protein digestion and their related enzymes.
Luminal digestion by gastric and pancreatic proteases
Membrane digestion by brush-border peptidases
Cytosolic digestion within epithelium of small peptides
Give 2 substances absorbed in the small intestine.
Amino acids
Peptides
Intact protein absorbed in antigenic quantities
Describe digestion by gastric pepsin. (2)
10-20% digestion
Endopeptidases
Describe digestion by pancreatic peptidases. (3)
E.g., trypsin
Endopeptidases and exopeptidases
Short peptides (2-6AA) and free amino acids
Describe protein digestion by membrane and cytosolic peptidases. (3)
Endo, exo or dipeptidases
Many different types
Free amino acids
What is acid microclimate used for?
Peptide absorption
H+ coupled di/tripeptide transport
What follows peptide absorption?
Cytosolic peptide digestion or export by unknown basolateral transporter
Give 3 drugs which utilise peptide carriers.
Angiotensin-converting enzyme (ACE) inhibitors
B-lactam antibiotics
Prodrugs (Val-acyclovir)
Give 3 types of amino acid transporters.
Neutral
Cationic
Anionic
Give the function of the apical membrane in amino acid absorption. (3)
Mainly coupled to ion uptake
Secondary active transport
Accumulation within epithelial cells
What is the role of the basolateral membrane in amino acid absorption?
Mainly facilitated diffusion
Give 3 key points in lipid digestion and absorption.
Low water solubility
Solubilisation
Digestion
Absorption
Re-esterification of fatty acids
Transport to blood
Describe triglycerides (dietary lipids).
Triesters of glycerol and long-chain fatty acids
Describe phospholipids (dietary lipids).
Subsitute 1 fatty acid chain with phospho-ester of organic base
Describe short chain fatty acids.
Minor - dairy
Describe lipid digestion. (5)
Detergent emulsification
Digestion by lipases produces micelles
Diffusion into epithelial cells
Resynthesis of triglycerides
Release as chylomicrons
Describe emulsification (stage 1) of lipid digestion. (3)
Begins with chewing, grinding and mixing of food
Increases oil-water interface area
Stabilised by bile salts and phospholipids
Describe digestion (stage 2) of lipids. (3)
Gastric and pancreatic lipases
Co-lipase
Triglycerides to 2 fatty acids and monoglyceride
What are micelles? (3)
Polymolecular aggregates 5nm
Monoglyceride, fatty acids, bile salts
Cholestrol and fat-soluble vitamins
Close approximation to enterocyte microvilli for absorption
Describe stage 3 of lipid digestion.
Diffusion down gradient
Describe stage 4 of lipid digestion.
Driven by re-esterification of fatty acids to triglycerides within epithelial cells
Describe stage 5 of lipid digestion.
Released across basolateral membrane as chylomicrons
How do digested lipids enter the blood?
Via lymph system
What other molecules follow the same route of absorption as lipids?
Fat soluble vitamins (A, D, E, K)
