Gastric Juice: Definition, Function, Production, Mechanism and Composition of This Digestive Fluid

It is a digestive fluid, acidic and thin, watery, and secreted by glands in the mucous membrane of the stomach.


As soon as you put food in your mouth, your stomach releases gastric juice. This liquid mixture will help dissolve food once it reaches the stomach and begins digestion.

How does your body make gastric juice?

The food that you chew and swallow is called a bolus. This mixes with gastric juices secreted by special glands found in the stomach lining.

They include the cardiac glands in the upper part of the stomach, the oxyntic glands in the main body of the stomach, and the pyloric glands in the antrum or the lowest part of the stomach.

Each of the glands contains cells that produce specific components called gastric juices.

Neck cells secrete bicarbonate and mucus, parietal cells secrete hydrochloric acid, central cells secrete pepsinogen, and enteroendocrine cells secrete various hormones.

However, not all glands in the stomach contain all types of cells.


Functioning or general mechanism of the stomach and gastric juice

The stomach is a muscular hollow organ. It takes food from the esophagus (or food tube), mixes it, breaks it down, and then passes it to the small intestine in small portions.

The entire digestive system comprises a muscular tube that runs from the mouth to the anus. The stomach is an enlarged pouch-like section of this digestive tract.

It is located on the left side of the upper abdomen and is shaped like a large coma, with its bulge pointing to the left.

The shape and size of the stomach vary from person to person, depending on things like people’s sex and build and how much they eat.

When the esophagus leads to the stomach, the digestive tract is generally kept closed by the muscles of the esophagus and the diaphragm. When you swallow, these muscles relax, and the lower end of the esophagus opens, allowing food to enter the stomach.

If this mechanism is not working correctly, acidic gastric juice could enter the esophagus, leading to heartburn or inflammation.

The upper left part of the stomach near the opening curves up towards the diaphragm. This part is called the fundus. It is usually filled with air that enters the stomach when you swallow.

In the most significant part of the stomach, called the body, food is stirred and divided into smaller pieces, mixed with acidic gastric juice and enzymes, and pre-digested.

At the stomach’s exit, the stomach’s body narrows to form the pyloric canal, where partially digested food passes in portions to the small intestine.

The stomach wall comprises several mucous membrane layers, connective tissue with blood vessels and nerves, and muscle fibers. The muscle layer only has three different sublayers.

The muscles move the stomach contents with such force that the solid parts of the food are crushed and ground and mixed into a smooth food pulp.

The inner mucous membrane (lining) has ample folds visible to the naked eye. These folds run toward the stomach’s outlet, providing “pathways” along which fluids can flow rapidly through the stomach.

If you look at the mucous membrane under a microscope, you can see many tiny glands. There are three different types of glands. These glands produce digestive enzymes, hydrochloric acid, mucus, and bicarbonate.

The ph of gastric juice

Your stomach secretes hydrochloric acid, but the pH of your stomach is not necessarily the same as the pH of the acid.

The pH of your stomach varies from 1-2 to 4-5. When you eat, your gut releases enzymes called proteases and hydrochloric acid to aid digestion.

Acid alone doesn’t help digestion much, but protein-cutting proteases work best in an acidic or low-pH environment, so after a protein-rich meal, the pH of the stomach can drop to 1 or 2.

However, buffers quickly raise the pH to 3 or 4.

After the food has been digested, the pH of your stomach 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 acid level representative of pure hydrochloric acid.

Chemical composition of gastric juice

Gastric juice is composed of digestive enzymes, hydrochloric acid, and other essential substances to absorb nutrients: about 3 to 4 liters of gastric juice are produced per day.

Hydrochloric acid in gastric juice breaks down food, and digestive enzymes break down protein.

Acid gastric juice also kills bacteria. Mucus covers the stomach wall with a protective layer. Along with the bicarbonate, this ensures that the hydrochloric acid does not damage the stomach wall.

Hydrochloric acid is a strong acid secreted by parietal cells and reduces the pH of your stomach to about.

Hydrochloric acid converts pepsinogen to pepsin and breaks down various nutrients apart from your food. It also kills bacteria that come along with your food.

Pepsinogen is secreted by the primary cells, and when it is in the presence of hydrochloric acid, it is converted to pepsin. Pepsin breaks down tertiary and secondary protein structures to facilitate the further work of digestive enzymes in the small intestine.

Gastric lipase is another digestive enzyme produced by significant cells. Helps break down short and medium-chain fats.

Amylase is also found in gastric juices, but the stomach does not produce it. This enzyme comes from saliva and travels along the bolus to the stomach.

Amylase breaks down carbohydrates, but it doesn’t take long to work in the stomach because the acidity stops it. But that’s okay; your small intestine produces more amylase later on.

Intrinsic factor is secreted by parietal cells and is necessary for your body to absorb vitamin B-12. This is essential for healthy nervous system function and blood cell production.

Finally, the gastric juice or juices contain water and mucus. Mucus is secreted by neck cells and helps coat and protect the stomach lining from the acidic environment.