What's in the Stomach's Gastric Juice?

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The food you chew and swallow (called a bolus) mixes with the gastric juices secreted by special glands found in the lining of your stomach. They include the cardiac glands at the top part of the stomach, the oxyntic glands in the main body of the stomach and the pyloric glands, located in the antrum or the lowest part of the stomach.

Each of the glands contains cells that make specific components that together are called the gastric juices.

Neck cells secrete bicarbonate and mucous, parietal cells secrete hydrochloric acid, chief cells secrete pepsinogen, and enteroendocrine cells secrete various hormones. Not all stomach glands contain every type of cell.

Breaking Down the Gastric Juices

Gastric juice is made up of water, electrolytes, hydrochloric acid, enzymes, mucus and intrinsic factor. Hydrochloric acid is a strong acid secreted by the parietal cells, and it lowers the pH of your stomach to around 2. Hydrochloric acid converts pepsinogen into pepsin and breaks various nutrients apart from the food you eat. It also kills bacteria that comes along with your food.

Pepsinogen is secreted by chief cells, and when it's in the presence of hydrochloric acid, it's converted to pepsin. Pepsin breaks apart tertiary and secondary protein structures to make it easier for the digestive enzymes in the small intestines to work later.

Gastric lipase is another digestive enzyme made by the chief cells.

It helps break down short and medium chain fats.

Amylase is also found in gastric juices, but it isn't made by the stomach, it comes from saliva and travels with the bolus into the stomach. Amylase breaks down carbohydrates, but it doesn't have much time to work on the stomach because the acidity stops it.

But that's okay, your small intestine makes more amylase later on.

Intrinsic factor is secreted by parietal cells and is necessary for your body to absorb vitamin B-12, which is essential for healthy nervous system function and blood cell production. Finally, the gastric juices contain water and mucus. The mucus is secreted by the neck cells and helps coat the protect your stomach lining from the acid environment.

Your stomach muscles squeeze and churn to mix the bolus with the digestive juices. The liquidy mixture is called chyme, and when it's ready, your stomach squirts the chyme into the small intestine where digestion and absorption of food continues.

Sources:

Gropper SS, Smith JL, Groff JL. "Advanced Nutrition and Human Metabolism." Sixth Edition. Belmont, CA. Wadsworth Publishing Company, 2013. 

Smolin LA, Grosvenor, MB. "Nutrition: Science and Applications." Third Edition. Wiley Publishing Company, 2013.

United States Department of Health and Human Services, National Digestive Diseases 
Information Clearinghouse (NDDIC). "Your Digestive System and How It Works." 

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