What structure regulates the passage of chyme into the small intestine?

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.