pylorussfincter

The pyloric sphincter, also called the pylorus, is a thick ring of smooth muscle at the distal end of the stomach that forms a functional gateway between the stomach and the duodenum. It sits at the junction of the gastric antrum and the first part of the small intestine and regulates the passage of gastric contents into the small bowel while limiting backflow.

Anatomy and control: The sphincter is part of the pyloric region and works together with the pyloric canal to mediate opening and closing of the gastric outlet. Its tone and opening are modulated by the autonomic nervous system, particularly vagal (parasympathetic) input that promotes relaxation for gastric emptying and sympathetic input that can increase constriction. Hormones such as gastrin and cholecystokinin also influence motility and meal-related regulation.

Physiology: During a meal, coordinated rhythmic antral contractions propel small amounts of chyme toward the pylorus. The sphincter periodically opens to allow chyme to enter the duodenum in a controlled, regulated manner, and immediately constricts to prevent large, rapid emptying. This makes gastric emptying a pulsatile process influenced by meal composition, osmolarity, and duodenal feedback.

Clinical relevance: Hypertrophy of the pyloric muscle in infants causes hypertrophic pyloric stenosis, presenting with projectile, nonbilious vomiting and dehydration; treatment is surgical pyloromyotomy. In adults, pyloric dysfunction or stenosis from peptic disease, scarring, or tumors can cause gastric outlet obstruction and may require endoscopic dilation or surgical intervention.