What Is the pH of the Stomach?

pH and Acidity of the Stomach

Acidity in human stomach, illustration

Your stomach secretes hydrochloric acid, but the pH of your stomach isn't necessarily the same as the pH of the acid!

pH of the Human Stomach

The pH of your stomach varies, from 1-2 up to 4-5. When you eat, the stomach releases enzymes called proteases as well as hydrochloric acid to aid in digestion. By itself, the acid doesn't really do much for digestion, but the proteases that cleave proteins work best in an acidic environment or low pH, so after a high-protein meal, your stomach pH may drop to as low as 1 or 2.

However, buffers quickly raise the pH back to 3 or 4. After the meal has been digested, your stomach pH returns to a resting level of about 4 or 5. Your stomach secretes acid in response to food, so first thing in the morning you can expect a slightly acidic stomach pH, but not an acidic level representative of pure hydrochloric acid.

Chemical Composition of Gastric Juice

The liquid inside your stomach is called gastric juice. It isn't just acid and enzymes, but a complex mixture of several chemicals. Take a look at the molecules, the cells that make them, and the function of the different components:

  • Water - Water doesn't affect the pH of the stomach, but it does serve to provide enough liquidity that food, enzymes, and acids can readily mix together. Some enzymes require water in order to function.
  • Mucous - Mucous (or mucus) is produced by cells in the mouth. esophagus, and stomach. It eases the passage of food through the gastrointestinal tract and protects the lining of the stomach from being attacked by acid. Neck cells also secrete bicarbonate, which buffers the acid and controls pH.
  • Hydrochloric Acid - This potent acid is secreted by the parietal cells of the stomach. It kills bacteria and other potential pathogens in food and converts the enzyme pepsinogen into pepsin, which breaks secondary and tertiary proteins into smaller, more easily digested molecules.
  • Pepsinogen - Pepsinogen is secreted by chief cells in the stomach. Once it's activated by low pH, it helps digest proteins.
  • Hormones and Electrolytes - Gastric juice also contains hormones and electrolytes, which aid in organ function, food digestion, and nutrient absorption. The enteroendocrine cells secrete multiple hormones.
  • Gastric Lipase - This is an enzyme made by chief cells in the stomach that aids in breaking up short-chain and medium-chain fats.
  • Intrinsic Factor - The parietal cells of the stomach secrete intrinsic factor, which is necessary for vitamin B-12 absorption.
  • Amylase - Amylase is an enzyme found primarily in saliva, where it acts to break down carbohydrates. It's found in the stomach because you swallow saliva as well as food, but it is inactivated by the low pH. Additional amylase is secreted into the small intestine.

The mechanical churning action of the stomach mixes everything together to form what is called chyme. Eventually, chyme leaves the stomach and processed to the small intestine so that the acid can be neutralized, digestion can proceed, and nutrients may be absorbed.