The stomach, typically a bit less than a foot in length, functions as a reservoir for swallowed food. The volume of our stomach depends on the quantity of food therein. An empty stomach may have a volume of only 1 to 3 ounces (approximately 50 to 75 milliliters) whereas a full stomach can expand to volumes of 2 to 3 quarts (approximately 2 to 3 liters).
The stomach is a very muscular organ. It churns food and mixes it with stomach juice. Stomach juice contains hydrochloric acid (HCl), which renders the stomach a very acidic environment (pH 1.5 to 2.5). A proteindigesting enzyme is also found in stomach juices. The presence of this enzyme, along with the acidic environment, will begin protein digestion. On the average, our stomach may produce about 2 to 3 quarts (approximately 2 to 3 liters) of stomach juice daily. Beyond protein digestion, the acidic stomach juice also kills most bacteria in foods.
Our stomach is sealed at both ends by tight muscular enclosures called sphincter muscles. This prevents acidic juices from entering the esophagus at one end and also allows separation between the stomach and small intestine at the other end. If stomach juice is able to reflux into our esophagus it can produce a burning sensation commonly referred to as heartburn. This is why chronic heartburn is routinely treated with antacids, as they attempt to neutralize the acid in the stomach. Other drugs may be used that attempt to decrease acid production by the stomach
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