PHIS 206 Lecture Notes - Lecture 25: Motilin, Digestive Enzyme, Exopeptidase
2 May 2018
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Lecture 25: Digestive Secretions
Small Intestine
• Three Regions
o Duodenum (∼30 cm long)
o Jejunum (∼2.5 m)
o Ileum (∼3-4 m)
o Visually, the regions are similar, but do vary in types of glands, absorptive
abilities.
o Most digestion occurs in the duodenum, most absorption in the jejunum.
Small Intestine Mobility
• Segmentation
o A mixing motility that ensures excellent contact between food and digestive
enzymes
o Mixes all the food with the enzymes (mixing motility pattern)
• Peristalsis
o A propulsive motility that moves material in a caudad direction
MMC (Migrating Motility Complex)
• (Migrating Myoelectric Complex, Intestinal Housekeeper, or ”Interdigestive
Housekeeper”)
• Waves of contractions that occur between meals to move debris and bacteria forward
• Stimulated by the hormone motilin Feeding inhibits motilin release, and the MMC
• This only happens between meals → DOES NOT HAPPEN WHEN EATING
Enter Pancreas
• Pancreatic Secretions
o Most of the secretions in the small intestine come from the pancreas
o Cells of pancreas release bicarbonate (duct cells) and digestive enzymes (acinar
cells)
Pancreatic Enzymes
• Pancreatic Secretions
o Many pancreatic enzymes are released in an inactive form, to be activated by
trypsin (also released by pancreas in inactive form).
o This is a precaution against autodigestion.
o Unfortunately, this precaution can fail → Pancreatitis (inflammation of the
pancreas)
o Pancreatic Enzymes must function in a more alkaline environment. (Reason for
addition of HCO− 3 )
• Protein Digestion Enzymes
o Carboxypeptidase, Chymotrypsin, Endopeptidase Family, Exopeptidase Family
• Carbohydrate Digestion Enzymes
o Pancreatic Amylase (release in active form - no threat to pancreas)
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Document Summary
Small intestine: three regions, duodenum ( 30 cm long, jejunum ( 2. 5 m) Ileum ( 3-4 m) abilities: visually, the regions are similar, but do vary in types of glands, absorptive, most digestion occurs in the duodenum, most absorption in the jejunum. Small intestine mobility: segmentation, a mixing motility that ensures excellent contact between food and digestive enzymes, mixes all the food with the enzymes (mixing motility pattern, peristalsis, a propulsive motility that moves material in a caudad direction. Mmc (migrating motility complex) (migrating myoelectric complex, intestinal housekeeper, or interdigestive. Housekeeper : waves of contractions that occur between meals to move debris and bacteria forward, stimulated by the hormone motilin feeding inhibits motilin release, and the mmc, this only happens between meals does not happen when eating. Enter pancreas: pancreatic secretions, most of the secretions in the small intestine come from the pancreas, cells of pancreas release bicarbonate (duct cells) and digestive enzymes (acinar cells)
