Pyloric sphincter

The pyloric sphincter is a thickened ring of circular smooth muscle located at the distal end of the pyloric canal, marking the junction between the stomach and the first part of the duodenum (gastroduodenal junction). It surrounds the pyloric orifice and functions as a physiological valve that regulates the passage of chyme from the stomach into the duodenum.

The pyloric sphincter remains tonically contracted and relaxes intermittently to allow small amounts of well-mixed chyme to enter the duodenum. It also prevents the reflux of duodenal contents, including bile and pancreatic secretions, back into the stomach. Its activity is controlled by neural and hormonal mechanisms, including the enteric nervous system and gastrointestinal hormones.

Innervation

• Parasympathetic: Vagus nerve.

• Sympathetic: Greater splanchnic nerves via the coeliac plexus.

Clinical correlate

• In congenital hypertrophic pyloric stenosis in infants, the hypertrophy of the pyloric sphincter causing gastric outlet obstruction, classically presenting with projectile non-bilious vomiting in infants.