Digestive Secretion List
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For the Digestive System page, see Anatomy/Digestive System
Various parts of the digestive tract secrete many enzymes and fluids. This page is a comprehensive list of those secretions, their source, and their functions.
- Enzymes speed up digestive processes to make digestion faster.
- Hormones can stimulate digestion, and the release of hormones into the organs.
- Mucus can protect the inner wall of organs, as well as lubricating them for movement.
|Hormone Name||Produced By||Secreted By||Method of Stimulation||Effect||Notes (if applicable)|
|Cholecystokinin (CCK)||L-cells in the mucosal epithelium of the small intestine||Duodenum||Fatty acids and peptides||Causes release of digestive enzymes and bile from the pancreas and gallbladder, respectively; slightly decreases gastric secretion; causes contraction of the gallbladder & relaxation of the hepatopancreatic ampullar sphincter; strongly decreases gastric motility; hunger suppressant||Induces drug tolerance to opioids and is implicated in the pain hypersensitivity during opioid withdrawal; peptide|
|Gastric Inhibitory Peptide (GIP)||K cells, found in the mucosa of the duodenum and jejunum||K cells, found in the mucosa of the duodenum and jejunum||n/a||Induces insulin secretion; has significant effect on fatty acid metabolism||Does NOT neutralize stomach acid (that's secretin); absence of GIP receptors correlated with resistance to obesity|
|Gastrin||G cells in the antrum of the stomach, duodenum, and pancreas||G cells of the duodenum and in the pyloric antrum of the stomach||Distension; partially digested proteins, autonomic stimulation, ingestion of alcohol or caffeine – release inhibited by stomach pH of 2 (negative feedback) & somatostatin, secretin, gastroinhibitory peptide, vasoactive intestinal peptide, glucagon, calcitonin||Stimulates secretion of gastric acid (HCl) by the parietal cells in the stomach; causes a minor increase in gastric motility; stimulates parietal cell maturation & fundal growth; induces pancreatic secretions & gallbladder emptying||Peptide; found primarily in big (34), little (17), & mini (14) forms, with numbers referring to amino acid count. Optimum pH 5-7|
|Motilin||M cells in the small intestine, esp. duodenum & jejunum||M cells in the small intestine, esp. duodenum & jejunum||Alkaline pH in the duodenum||Increases the migrating myoelectric complex component of GI motility; stimulates the production of pepsin; increases release of pancreatic polypeptide & somatostatin; "housekeeper of the gut" – improves peristalsis in the small intestine & clears the gut to prepare for the next meal||n/a|
|Secretin (SCT)||Cytoplasmic secretory granules of S-cells, in the mucosa of the duodenum & (in smaller numbers) the jejunum||Duodenum||Low duodenal pH (2-4.5) – release inhibited by H2 antagonists||Regulates pH of duodenal contents; increases watery bicarbonate solution from pancreatic & bile duct epithelium; triggers increased release from pancreas following oral glucose intake; inhibits gastrin release from stomach from G cells; stimulates pepsin secretion from chief cells & release of glucagon, pancreatic polypeptide, somatostatin||Used in medical field, esp. in pancreatic function tests (increases pancreatic secretions); first hormone identified|
|Enzyme Name||Source||Substrates||Products||Notes (if applicable)|
|Aminopeptidase||Small intestine||Amino acid at amino end of peptides||Amino acids & peptides||n/a|
|Carboxypeptidase||Pancreatic acinar cells||Amino acid at carboxyl end of peptides||Amino acids & peptides||Activated from procarboxypeptidase by trypsin; optimum pH varies|
|Chymotrypsin||Pancreatic acinar cells||Proteins||Peptides||Activated from chymotrypsinogen by trypsin; optimum pH 7.8|
|Deoxyribonuclease||Pancreatic acinar cells||DNA||Nucleotides||n/a|
|Dipeptidase||Small intestine||Dipeptides||Amino acids||n/a|
|Elastase||Pancreatic acinar cells||Proteins||Peptides||Activated from proelastase by trypsin|
|Gastric lipase||Stomach chief cells||Triglycerides||Fatty acids & monoglycerides||Optimum pH 4-5|
|Lactase||Small intestine||Lactose||Glucose & galactose||n/a|
|Lingual lipase||Lingual glands in tongue||Triglycerides (fats & oils) & other lipids||Fatty acids & diglycerides||Optimum pH 4.5-5.5|
|Nucleosidases & phosphatases||Small intestine||Nucleotides||Nitrogenous bases, pentoses, phosphates||n/a|
|Pancreatic amylase||Pancreatic acinar cells||Starches||Maltose, maltotriose, α-dextrins||Optimum pH 6.7-7.0|
|Pancreatic lipase||Pancreatic acinar cells||Triglycerides emulsified by bile salts||Fatty acids & monoglycerides||Optimum pH 8.0|
|Pepsin||Stomach chief cells||Proteins||Peptides||Activated from pepsinogen by pepsin & HCl; optimum pH 1.5-1.6|
|Ribonuclease||Pancreatic acinar cells||RNA||Nucleotides||n/a|
|Sucrase||Small intestine||Sucrose||Glucose & fructose||n/a|
|Salivary amylase||Salivary glands||Starches||Maltose, maltotriose (trisaccharide), α-dextrins||Optimum pH 6.7-7|
|Trypsin||Pancreatic acinar cells||Proteins||Peptides||Activated from trypsinogen by enterokinase; optimum pH 7.8-8.7|
- Saliva is a fluid secreted by the salivary glands. It moistens and lubricates and has an optimum pH of 6.5-7.5.
- Lysozyme is an enzyme secreted by the salivary glands. It kills bacteria.
- Mucus is a fluid secreted by the foveolar cells in the stomach. It protects the stomach wall.
- Chymosin is a fluid secreted by the chief cells of the stomach. It coagulates milk and has an optimum pH of 3.5.
- Hydrochloric acid is a fluid secreted by the parietal cells of the stomach. It kills bacteria, activates pepsinogen -> pepsin, and lowers the pH of the stomach. Its acidity denatures proteins, aiding in protein digestion. It has a pH of 1.
- Intrinsic factor is an enzyme (glycoprotein) secreted by the parietal cells of the stomach. It assists in the absorption of vitamin B12 by protecting the acid-intolerant substance as it goes through the stomach. It has an optimum pH of 7.
- Bile is a fluid consisting primarily of bile salts and bilirubin produced by the hepatocytes of the liver and secreted by the gallbladder. It assists in the digestion of lipids and has an optimum pH of 7.5-8.8.
- Bicarbonate ions are secreted by the pancreas. They are alkaline and are employed to control pH levels.