Intestinal Phase
Monday, 25 October 2021 9:20 AM
Intestinal secretions
- Pancreatic secretion
- Bile
- Small intestines secretion
- Brunner's gland secretion
Pancreatic secretion
- Pancreatic enzymes
□ Acini cells perform exocrine function
® Secrete enzymes
□ Duct cells
® Secrete bicarbonate
□ Digestion of protein
® Trypsin and chymotrypsin
□ Digest protein into peptides of various sizes
® Carboxypolypeptidase
□ Splits peptides into individual amino acids
® Serine proteases
□ Trypsin / chymotrypsin / elastase
□ All produced in the pancreas
□ Serine is the nucleophilic amino acid at the
enzymes active site
□ Similar pH around 8
□ Endopeptidases
® Cleave the peptide bonds within a
polypeptide
® Have specificities for different amino acids
at the P1 site, the amino acid after which
the enzyme cleaves
® Trypsin cleaves after basic amino acids e.g
lysine and arginine
® Chymotrypsin cleaves after aromatic amino
acids
® Elastase cleaves at bonds adjacent to
residents with small non polar chains
□ Digestion of carbohydrates
® Amylase
□ Hydrolyzes starches / glycogen / carbohydrates
, acids
® Elastase cleaves at bonds adjacent to
residents with small non polar chains
□ Digestion of carbohydrates
® Amylase
□ Hydrolyzes starches / glycogen / carbohydrates
into disaccharides
□ Digestion of fat
® Lipase
□ Hydrolyzes neutral fat into fatty acids and
monoglycerides
® Cholesterol esterase
□ Hydrolyzes cholesterol esters
® Phospholipase
□ Splits phospholipids into fatty acids
- Trypsin inhibitor
□ Prevents digestion of the pancreas itself
□ Serine protease inhibitor
- Bicarbonate ions
□ Neutralizes the HCL emptied into the duodenum from the
stomach
- Proteolytic digestion in the small intestines
□ Proteolytic enzymes secreted from the pancreas are inactive
precursors
® Activated when they reach small intestines
□ Conversion of the precursors to the active enzymes in the
lumen of the small intestines
® Trypsinogen converted to trypsin by enterokinase
□ Active trypsin then cleaves other precursors of proteolytic
enzymes and activates them
® Chymotrypsin / proelastase
- Hormonal control of pancreatic secretion by small intestines
□ By S cells in mucosa of duodenum and jejunum
® In response to increase acid in stomach
® Secrete secretin
® Increases pancreatic bicarbonate secretion
® Neutralizes acid
□ I cells in the mucosa of duodenum and jejunum
® In response to increase intestinal fatty acids and amino
acids
□ Increase cholecystokinin in small intestines
□ Increases plasma enzyme secretion
□ Increase digestion of fats / proteins
Biliary secretion
- Secreted by liver cells
- Concentrated / stored in gallbladder
Monday, 25 October 2021 9:20 AM
Intestinal secretions
- Pancreatic secretion
- Bile
- Small intestines secretion
- Brunner's gland secretion
Pancreatic secretion
- Pancreatic enzymes
□ Acini cells perform exocrine function
® Secrete enzymes
□ Duct cells
® Secrete bicarbonate
□ Digestion of protein
® Trypsin and chymotrypsin
□ Digest protein into peptides of various sizes
® Carboxypolypeptidase
□ Splits peptides into individual amino acids
® Serine proteases
□ Trypsin / chymotrypsin / elastase
□ All produced in the pancreas
□ Serine is the nucleophilic amino acid at the
enzymes active site
□ Similar pH around 8
□ Endopeptidases
® Cleave the peptide bonds within a
polypeptide
® Have specificities for different amino acids
at the P1 site, the amino acid after which
the enzyme cleaves
® Trypsin cleaves after basic amino acids e.g
lysine and arginine
® Chymotrypsin cleaves after aromatic amino
acids
® Elastase cleaves at bonds adjacent to
residents with small non polar chains
□ Digestion of carbohydrates
® Amylase
□ Hydrolyzes starches / glycogen / carbohydrates
, acids
® Elastase cleaves at bonds adjacent to
residents with small non polar chains
□ Digestion of carbohydrates
® Amylase
□ Hydrolyzes starches / glycogen / carbohydrates
into disaccharides
□ Digestion of fat
® Lipase
□ Hydrolyzes neutral fat into fatty acids and
monoglycerides
® Cholesterol esterase
□ Hydrolyzes cholesterol esters
® Phospholipase
□ Splits phospholipids into fatty acids
- Trypsin inhibitor
□ Prevents digestion of the pancreas itself
□ Serine protease inhibitor
- Bicarbonate ions
□ Neutralizes the HCL emptied into the duodenum from the
stomach
- Proteolytic digestion in the small intestines
□ Proteolytic enzymes secreted from the pancreas are inactive
precursors
® Activated when they reach small intestines
□ Conversion of the precursors to the active enzymes in the
lumen of the small intestines
® Trypsinogen converted to trypsin by enterokinase
□ Active trypsin then cleaves other precursors of proteolytic
enzymes and activates them
® Chymotrypsin / proelastase
- Hormonal control of pancreatic secretion by small intestines
□ By S cells in mucosa of duodenum and jejunum
® In response to increase acid in stomach
® Secrete secretin
® Increases pancreatic bicarbonate secretion
® Neutralizes acid
□ I cells in the mucosa of duodenum and jejunum
® In response to increase intestinal fatty acids and amino
acids
□ Increase cholecystokinin in small intestines
□ Increases plasma enzyme secretion
□ Increase digestion of fats / proteins
Biliary secretion
- Secreted by liver cells
- Concentrated / stored in gallbladder
