The pyloric sphincter is a tonically contracted ring of thickened circular smooth muscle at the gastroduodenal junction, palpable as a firm olive-shaped mass in hypertrophic pyloric stenosis. Pyloric opening is controlled by the coordination of vagal drive, enteric reflexes, gastric acid output, and duodenal feedback (cholecystokinin, secretin).
| Origin | Circular smooth muscle of the distal antrum of the stomach, which thickens progressively to form the pyloric sphincter ring at the gastroduodenal junction |
|---|---|
| Insertion | Continuous with the circular smooth muscle of the proximal duodenum (duodenal cap); the pyloric channel is surrounded by the sphincter ring and ends at the pyloric orifice |
| Nerve Supply | Vagus nerve (CN X) parasympathetic — promotes pyloric opening and gastric emptying; sympathetic via the coeliac plexus — promotes pyloric contraction; enteric nervous system (Auerbach's plexus) — intrinsic regulation of pyloric cycling |
| Blood Supply | Right gastric artery; gastroduodenal artery branches |
| Actions | Regulates the rate of gastric emptying by controlling the pyloric orifice diameter; opens intermittently to allow small boluses of chyme to pass into the duodenum in coordination with antral peristalsis and duodenal receptive relaxation; prevents duodenogastric reflux of bile and pancreatic juice |
|---|
Infantile hypertrophic pyloric stenosis (IHPS) is caused by progressive smooth muscle hypertrophy of the pyloric sphincter in infants 2-8 weeks old, producing projectile non-bilious vomiting, weight loss, and a palpable olive in the right hypochondrium. Ultrasound confirms the diagnosis (pyloric muscle thickness greater than 4 mm, canal length greater than 16 mm). Ramstedt pyloromyotomy divides the hypertrophied circular muscle longitudinally without opening the mucosa, immediately relieving the obstruction. In adults, pyloric stenosis from peptic ulcer disease or carcinoma requires endoscopic dilation or surgical bypass.
Progressive pyloric sphincter circular muscle hypertrophy in an infant 2-8 weeks old produces projectile non-bilious vomiting after feeds with a palpable right hypochondrial olive; ultrasound demonstrates pyloric muscle thickness greater than 4 mm and canal length greater than 16 mm; laparoscopic Ramstedt pyloromyotomy provides immediate definitive relief.
