Food that has been churned in the stomach and mixed with gastric juices and hydrochloric acid, is known as chyme. Rhythmic involuntary muscle contractions of the digestive tract, known as peristalsis, move chyme along to the small intestine. The structure that regulates the passage of chyme into the small intestine is called the pyloric sphincter or valve. As chyme with its acidic ph enters the duodenum, the upper portion of the small intestine,it becomes neutralized. By the time the chyme has been acted upon by bile and pancreatic juice, as well as intestinal juice, the process of digestion is complete inside the small intestine. Absorption of nutrients occurs by tiny projections in the intestinal lining known as villi, where they enter the circulation and are transported throughout the body.