1.3.2. Hormones of the Digestive System

α-Amylase

This refers to an enzyme that acts on starch and α-linked polysaccharides, hydrolyzing them mainly into dextrins and maltose in the mouth.

Lingual Lipase

This refers to an enzyme that acts on triglycerides, producing diglycerides and free fatty acids.

Pepsin

This refers to a proteolytic enzyme, activated from pepsinogen in the presence of hydrochloric acid, that breaks protein peptide bonds to form peptides and amino acids.

Gastric Lipase

This refers to an enzyme that hydrolyzes triglycerides into diglycerides and free fatty acids in the stomach.

Lipase

This refers to an enzyme that digests fat in the presence of bile salts, producing monoglycerides and fatty acids, which are incorporated into micelles in the small intestines.

Cholesterol Esterase

This refers to an enzyme that acts on sterols such as cholesterol, producing cholesterol-related products and fatty acids that become incorporated into micelles.

Pancreatic α-Amylase

This refers to an enzyme that acts on starch and dextrins, producing dextrins and maltose.

Trypsin

This refers to a proteolytic enzyme activated from trypsinogen that breaks interior peptide bonds of proteins and polypeptides.

Chymotrypsin

This refers to a proteolytic enzyme activated from chymotrypsinogen that hydrolyzes interior peptide bonds of proteins and peptides.

Carboxypeptidase

This refers to an enzyme activated from procarboxypeptidase that removes amino acids from the terminal end of polypeptides.

Ribonuclease and Deoxyribonuclease

These refer to enzymes that hydrolyze RNA and DNA, respectively, into mononucleotides.

Elastase

This refers to an enzyme that acts on fibrous protein such as elastin, producing peptides and amino acids.

Enterokinase

This refers to an intestinal enzyme that activates trypsinogen to form trypsin.

Aminopeptidase and Dipeptidase

These refer to enzymes located in the enterocyte cytosol that cleave amino acids from the amino end of proteins or split dipeptides.

Sucrase

This refers to an enzyme that hydrolyzes sucrose into glucose and fructose.

α-Dextrinase (Isomaltase)

This refers to an enzyme that hydrolyzes dextrins/isomaltose to form glucose.

Maltase

This refers to an enzyme that hydrolyzes maltose to form glucose.

Lactase

This refers to an enzyme that hydrolyzes lactose into glucose and galactose.

Nucleotidases

These refer to enzymes that hydrolyze nucleic acids/nucleotides into smaller nucleotide components and phosphates.

Nucleosidase and Phosphorylase

These refer to enzymes that act on nucleosides, producing purines, pyrimidines, and pentose phosphate.

Gastrin

This refers to a hormone released mainly from G cells of the gastric mucosa and duodenum in response to peptides, amino acids, caffeine, antral distention, some alcoholic beverages, and vagal stimulation. It stimulates HCl and pepsinogen secretion and increases gastric antral motility.

Secretin

This refers to a hormone released from S cells of the duodenum in response to acid entering the small intestine. It increases pancreatic water and bicarbonate secretion, decreases duodenal motility, and increases mucus output.

Cholecystokinin (CCK)

This refers to a hormone released from I cells of the duodenum in response to peptides, amino acids, fats, and HCl. It stimulates pancreatic enzyme secretion, contracts the gallbladder, slows gastric emptying, and increases colonic motility.

Gastric Inhibitory Peptide / Glucose-Dependent Insulinotropic Peptide (GIP)

This refers to a hormone released from K cells of the duodenum and jejunum in response to glucose and fat, producing reduced intestinal motility.

Motilin

This refers to a hormone released from M cells of the duodenum and jejunum during interdigestive periods and alkaline duodenal pH, promoting gastric emptying and GI motility.

GLP-1

This refers to a hormone released from L cells of the small intestine and colon in response to glucose, fat, and short-chain fatty acids. It prolongs gastric emptying, inhibits glucagon release, and stimulates insulin release.

GLP-2

This refers to a hormone released from L cells of the small intestine and colon in response to glucose, fat, and short-chain fatty acids. It stimulates intestinal growth and promotes nutrient digestion and absorption.