Hormones and the Digestive System
There are four main hormones that affect the digestive system. These are gastrin, secretin, cholecystokinin (CCK), and gastric inhibitory peptide (GIP).
The secretion of gastrin is stimulated by food arriving in stomach. Gastrin causes the gastric glands to secrete pepsinogen and hydrochloric acid. Pepsinogen helps with the digestion of protein. Hydrochloric acid kills bacteria in the food, and creates the optimal pH balance for gastric enzymes to function.
Secretin is secreted in the duodenum in response to the acidic chyme (i.e., food stuffs) entering the small intestine from the stomach. The primary target of secretin is the pancreas. Secretin stimulates the pancreas and bile ducts to release sodium bicarbonate to neutralize the acid. The sodium bicarbonate flows into the duodenum through the pancreatic duct. The secretion of secretin is turned off when the pH level in the duodenum returns to normal.
Cholecystokinin (CCK) is secreted in the duodenum in response to partially digested fat and protein (i.e., food stuffs) arriving from the stomach. CCK stimulates the release of digestive enzymes in the pancreas, and stimulates the contraction of the gall bladder to empty bile into the duodenum. The pancreatic enzymes and bile flow through ducts into the duodenum. The pancreatic enzymes assist in the breakdown of fats, proteins, and carbohydrates. Bile aids in the digestion and absorption of fats.
Gastric inhibitory peptide (GIP) produced in the duodenum decreases the stomach contractions churning the chyme, and slows the emptying of the stomach into the duodenum. This gives the small intestine more time to effectively digest the fats, proteins, and carbohydrates.