Physiology of the small intestine Flashcards
What glands in the small intestine secrete mucus?
Brunner’s glands
What is the function of motilin hormone?
Stimulates migrating motor complexes (MMCs) via both the enteric and autonomic nervous systems.
What is the function of Vasoactive intestinal peptide (VIP) hormone?
Increases blood flow to the GI tract
What is the function of CCK (cholecystokinin) and secretin?
Inhibits gastric motility and secretion and controls pancreatic and biliary secretion.
What are the main secretions of the small intestine?
Mucus, water and hormones
Name the hormones secreted by the small intestine.
Motilin Vasoactive intestinal peptide (VIP) Gastric inhibitory peptide (GIP) Cholecystokinin (CCK) Secretin
What cells (x2) in the pancreas secrete enzymes/alkali?
Acinar cells - enzymes (zymogens) (activated by membrane bound enterokinase)
Duct cells - alkali
How is HCO3- secreted from the pancreatic duct into the intestinal lumen?
(CO2 + H2O H2CO3 HCO3- + H+)
HCO3- secreted into duct lumen
H+ are pumped out of duct cells and released into the blood
How are fats digested in the small intestine?
1) Fats are emulsified by bile salts and phospholipids
2) Triglycerides are digested by pancreatic lipase to monoglycerides and fatty acids.
3) Held in micelles
How are fats absorbed in the small intestine?
1) Monoglycerides and fatty acids diffuse into epithelial cell
2) Reassembled into triglycerides
3) Packaged into chylomicrons
4) Leave intestinal villus via its lymph vessel (thoracic duct - LSV)
Describe how starch is converted to monosaccharides.
Pancreatic amylase converts starch to maltose. Brush border enzymes (maltase, sucrose and lactase) break down products to glucose, fructose and galactose. Absorbed into blood.
How are dissacharides formed from monosaccharides?
Glycosidic bond by eliminating water
Glucose, galactose and fructose are absorbed from the intestinal lumen via what transporters and exit into the blood via which transporters?
Glucose + galactose - SGLT-1
Fructsoe - GLUT5 (facilitated diffusion)
All exit into blood via GLUT2 (facilitated diffusion)
How are proteins absorbed in the small intestine?
1) proteins digested by: trypsin, chymotrypsin and carboxypeptidase
2) Further by: dipeptidase and aminopeptidase into tri/dipeptides and free AAs
3) Enter epithelial cells and usually hydrolysed to AAs by cytosolic peptidase
Di/tripeptides and free AAs are absorbed from the intestinal lumen via what transporters and exit into the blood via which transporters?
AAs - Na+-amino acid cotransporters
Di/tripeptides - H+-dependent co-transporters
Exit into blood by facilitated diffusion
