Esophagus As you swallow that bite of pie, muscles in your mouth and throat propel it to your upper esophagus, the tube that connects your throat to your stomach. Muscles in the wall of your esophagus create synchronized waves — one after another — that propel the pie into your stomach. In this process, called peristalsis, muscles behind the bolus of pie contract, squeezing it forward, while muscles ahead of it relax, allowing it to advance without resistance. When the bolus reaches the lower end of your esophagus, pressure from the food signals a muscular valve — the lower esophageal sphincter — to relax and let the food enter your stomach.

Stomach After entering your stomach, the pie is broken down further. With its powerful muscles, the stomach begins churning and mixing the food into smaller and smaller pieces. Gastric juices, rich in acid and enzymes, pour out of glands that line your stomach. The acid and enzymes help break down food into a thick, creamy fluid called chyme. Once the chyme is well mixed, waves of muscle contractions propel it through the pyloric valve and into the first section of your small intestine (duodenum). The pyloric valve releases less than an eighth of an ounce of chyme at a time. The rest is held back for more mixing.