The pylorus is the opening at the lower end of the stomach that leads into the duodenum, forming the gateway through which digested food leaves the stomach. The term is also used for the surrounding region, including the muscular pyloric sphincter that regulates flow through the opening. Chyme passes through the pylorus in small, controlled spurts rather than as a continuous stream, allowing the small intestine to receive manageable amounts for further digestion and absorption. Disorders of the pylorus, such as narrowing from ulcers or congenital thickening in infants, cause obstruction with vomiting and weight loss. The plural of pylorus is pylori, a form most often met in anatomical and medical writing rather than in everyday nutrition discussion.