and the digestive system . The large, hollow organs of the GI tract contain a layer of muscle that enables their walls to move.
This movement pushes food and liquid through the GI tract and mixes the contents within each organ. The muscle behind the food contracts and squeezes the food forward, while the muscle in front of the food relaxes to allow the food to move through the digestive system.
# . : Food starts to move through the GI tract when eating. The tongue pushes the food into the throat and a small flap of tissue, called the epiglottis, folds over the windpipe to prevent choking and the food passes into the esophagus.
# . : After swallowing, the process becomes automatic. The brain signals the muscles of the esophagus and peristalsis begins.
# . : When food reaches the end of the esophagus, a ring-like muscle called the lower esophageal sphincter relaxes and lets food pass into the stomach. This sphincter usually stays closed to keep the contents in the stomach from flowing back into the esophagus.
# . : After food enters the stomach, the stomach muscles mix the food and liquid with digestive juices. The stomach slowly empties its contents, called chyme, into the small intestine.
# . : The muscles of the small intestine mix food with digestive juices from the pancreas, liver, and intestine, and push the mixture forward for further digestion. The walls of the small intestine absorb water and the digested nutrients into the bloodstream. As peristalsis continues, the waste products of the digestive process move into the large intestine.
# . : Waste products from the digestive process include undigested parts of food, fluid, and older cells from the lining of the GI tract. The large intestine absorbs water and changes the waste from liquid into stool. Peristalsis helps move the stool into the rectum.
# . : The lower end of the large intestine, the rectum, stores stool until it is pushed out of the anus during a bowel movement.
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