Pylorus

Overview

The pylorus is the distal part of the stomach that connects to the duodenum. It acts as a regulated gateway for chyme—the partially digested food—to enter the small intestine. The pylorus includes the muscular pyloric sphincter, which controls the rate of gastric emptying and prevents reflux of intestinal contents. Its strategic role in digestion makes it a critical anatomical and physiological structure.

Location

The pylorus is located at the terminal end of the stomach, in the right upper quadrant of the abdomen. It lies:

• Inferior to the liver and anterior to the L1 vertebra (also known as the transpyloric plane)

• Between the body of the stomach and the first part of the duodenum

It is positioned slightly to the right of the midline, and its precise location can vary slightly depending on stomach filling and body position.

Structure

The pylorus consists of two main anatomical parts:

• Pyloric antrum: The wider, proximal part that connects to the body of the stomach and serves as a chamber for food mixing

• Pyloric canal: The narrower, distal part that leads to the duodenum and houses the pyloric sphincter

Histologically, the pylorus features:

• Thick circular muscle layer: Forms the pyloric sphincter to control gastric outflow

• Mucosal glands: Predominantly mucus-secreting cells and G cells that release gastrin

• Rich vascular supply: From the right gastric and right gastroepiploic arteries

Function

The pylorus serves both mechanical and regulatory functions:

• Acts as a valve: Controls the passage of chyme from the stomach into the duodenum

• Regulates gastric emptying: Opens and closes rhythmically to allow properly digested food to pass in controlled amounts

• Mixes and grinds food: The pyloric antrum contributes to mechanical digestion by churning food into chyme

Physiological Role(s)

The pylorus plays essential roles in digestive physiology:

• Timing of digestion: Ensures that only suitably processed chyme is released into the small intestine for further digestion and absorption

• Hormonal regulation: Gastrin, secreted by G cells in the pyloric mucosa, stimulates acid secretion and enhances pyloric motility

• pH control: Delays gastric emptying until the duodenum is ready to neutralize acidic contents with bicarbonate-rich pancreatic juice

• Prevents duodenogastric reflux: The sphincter prevents bile and pancreatic enzymes from flowing backward into the stomach

Clinical Significance

The pylorus is commonly involved in several medical conditions:

• Pyloric stenosis: Most commonly seen in infants (congenital hypertrophic pyloric stenosis), it leads to gastric outlet obstruction and projectile vomiting

• Peptic ulcer disease: Ulcers in the pyloric region can cause scarring and narrowing of the canal, leading to obstruction

• Gastroparesis: Delayed gastric emptying, often due to diabetes or vagal nerve dysfunction, can affect pyloric function

• Pylorospasm: Spasmodic contraction of the pyloric sphincter may cause intermittent vomiting or delayed emptying

• Pyloroplasty: A surgical procedure to widen the pyloric canal, used in chronic obstruction or gastroparesis management

• Gastric cancer: Tumors near the pylorus may obstruct outflow and require partial or total gastrectomy

The pylorus is routinely evaluated during upper GI endoscopy and imaging studies (e.g., barium swallow, ultrasound) when symptoms like nausea, vomiting, or early satiety are present.