stomach

Organ that forms the first cavity in the digestive system of animals. In mammals it is a bag of muscle situated just below the diaphragm. Food enters it from the oesophagus, is digested by the acid and enzymes secreted by the stomach lining. The wall of the stomach contracts to mix the food with the digestive juice to help digestion of protein. After a while, partly digested food is then passed into the small intestine (duodenum). Some plant-eating mammals have multi-chambered stomachs that harbour bacteria in one of the chambers to assist in the digestion of cellulose.

The gizzard is part of the stomach in birds.