How the Digestive System Works

Digestion Process

Hormones control the regulation of the entire digestive process -- some even regulate your appetite. The hormones produced in the mucosa cells of the stomach and small intestines work by stimulating these organs and their digestive juices.

The three hormones responsible for the digestion of your sandwich are gastrin, secretin and cholecystokinin (CCK).


  • Gastrin gives the stomach the signal to produce acid. It also plays an important role in the growth of the stomach, small intestine and colon lining -- which, as you now know, is needed for absorbing nutrients and excreting digestive juices.
  • Secretin communicates with all the major digestive accessory organs. In the pancreas, a call from secretin causes the excretion of those helpful digestive juices. Then secretin calls the stomach, causing it to produce pepsin, an enzyme used to digest protein. Secretin's final call is the liver, which then produces more of that much-needed bile.
  • CCK talks to the little organs: the pancreas and the gallbladder. With the help of this hormone the pancreas grows and produces more enzymes. Once the gallbladder hears from CCK, it knows to release all the bile it has been storing for the liver.

As we mentioned, a few hormones also work to encourage you to start and stop eating that food. The first of these is ghrelin, which both the stomach and small intestine produce when there is no food in them. So, when ghrelin levels run high, your appetite is stimulated. Peptide YY, a hormone made in the gastrointestinal tract, works in an opposite manner. Once you finish that sandwich, it's excreted to quell your hunger.


Not surprisingly, nerves are involved in digestion regulation.

  • Extrinsic nerves are based in the unconscious part of the brain and in the spinal cord, and they need the help of the chemicals acetylcholine and adrenaline. Acetylcholine works with hormones to encourage the stomach and pancreas to make more digestive juices. But its main function involves the movement of the digestive organs. Once released by an extrinsic nerve, acetylcholine causes these organs' muscles to contract and move food through that long digestive tract. Adrenaline, on the other hand, relaxes these muscles when no food is in the system.
  • Intrinsic nerves are embedded all along the digestive tract, from the esophagus to the colon. These nerves don't get their signal from the brain but instead jump into action when your food stretches the walls of the various hollow digestive organs. Depending on the amount of stretching, these nerves release an abundant amount of substances that can either speed up or slow down the digestive process.