What is the role of the stomach in digestion?

Lawrence S. Friedman, MD
The stomach can be likened to a storage and processing facility, where the food is prepared for digestion.

This food warehouse can accommodate anything from a light afternoon snack to a five-course meal. Without this large storage capacity, people would have to eat small, frequent meals, and they'd be unable to drink large quantities of liquids at any given time.

But the stomach doesn't just hold food: muscles in the lower stomach also mix that food into a soft mush. This process is aided by the liquids we drink and by saliva, hydrochloric acid, and the enzyme pepsin. Hydrochloric acid and pepsin, produced by the glands that line the stomach, help break down proteins into their constituent amino acids. The stomach mucosa has a defense system, including an overlying layer of mucus and bicarbonate, to protect itself. After mixing, a once-palatable meal is reduced to a thick liquid called chyme.

The other important function of the stomach is delivering the resulting chyme to the small intestine in amounts it can handle. The involuntary contractions that push stomach contents along are governed by nerves in the stomach wall, which transmit electrical impulses to the brain. The nerves that carry impulses from the gastrointestinal (GI) tract, called visceral nerves, recognize stretching, pulling, or expansion (distension) of the muscles in the walls of the digestive tract. Pain can result when these sensations are excessive.
Lionel M. Bissoon, MD
Sports Medicine

The stomach is truly the gateway to good health for several reasons; once food enters the stomach it will secrete acid to accomplish the following:

  • Stomach acid digests food and prepares if for absorption.
  • Stomach acid will stimulate the production of mucus to protect the stomach wall from being damaged by the strong hydrochloric acid produced by the parietal cells.
  • Acid will sterilize the food, thus, killing bacteria, fungus, bacteria and parasites.
  • Acid will stimulate the production of Intrinsic Factor, which will attach to Vitamin B-12 and protect it form being destroyed by the acid.
  • The production of stomach acid will close the pyloric valve that will prevent undigested food from going into the intestines.
  • As part of digestion, the acid produced by the stomach will prepare the nutrients to be absorbed i.e. nutrients has to be exposed to acid before it can be absorbed in the intestines.
  • The stomach also produces an enzyme called Pepsinogen which when activated will start to digest protein in the stomach.

There are other actions of the stomach but the above are very critical for digestion of and absorption of nutrients.

Dr. Michael Roizen, MD
Internal Medicine
As food enters your stomach from your esophagus, your stomach mixes it up. Your stomach serves as your body's washing machine—mixing foods with acids, breaking apart foods into different nutrients. As you age, you not only have less digestive fluid in your stomach, but the fluid you do have has less acidity. That may seem like a good thing, but it means your body has a weakened ability to jackhammer out the proteins it needs for normal functioning. That's one of the reasons why pharmaceuticals have very different effects as you age.

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International bestselling authors of YOU: The Owner's Manual and YOU: On a Diet give you all the tools and know-how to stay young and defy the ageing process. Drawing lively parallels between your...

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.