Anatomy of the digestive system in adults, human digestive system. The digestive system begins with the oral cavity and the salivary glands as well as the thoracic esophagus in the thorax. Then it continues in the abdomen with the abdominal esophagus followed by the stomach to the right of the drawing followed by the duodenum. The pancreas appears transparent behind the duodenum and the stomach, and to the left of the picture is the liver. Below these organs, the small intestine in the center is surrounded by the large intestine made up of the ascending colon on the left, the transverse colon from left to right, and the descending colon on the right ending in the rectum.