The stomach is a small, hollow bag with muscular walls. It is both a food mixer and acid bath that receives, holds and digests food. This pouch-like organ is actually small, but as you eat the stomach wall quickly stretches to hold up to 3 liters. The powerful muscles lining the stomach churn and mash food, breaking up fats and proteins.
When you see or smell food, tiny stomach glands secrete gastric juice, mostly comprised of hydrochloric acid with a touch of the enzyme pepsin. The acid breaks down food and kills germs. Every day your stomach produces vast amounts of gastric acid, strong enough to digest the stomach itself. This is why protective mucous lines the stomach walls.
The stomach’s churning and mixing with gastric juice converts food into a thick liquid called chyme. After several hours, the chyme passes from the stomach into the small intestine. Compared to other creatures, the human stomach is not too exciting. The blue whale’s stomach can hold 2,000 pounds of food. The cow’s stomach is divided into four distinct sections that hold grass-chomping microbes. The jellyfish’s gastric cavity converts food into a soupy liquid that’s transferred directly into its circulatory system. Leftovers are expelled back out of the jellyfish’s stomach the same way it came in. Or how about the python’s stomach, which can stretch enormously and hold a fully intact deer!