The pylorus, derived from the Greek word for “gatekeeper,” is the final, narrow segment of the stomach. This muscular junction acts as a precise physiological valve, connecting the stomach to the small intestine. It serves as a regulatory mechanism, controlling the exit point for partially digested food and ensuring its controlled delivery to the next stage of digestion.
Anatomical Location in the Digestive System
The pylorus is situated in the upper portion of the abdominal cavity, generally lying in the epigastric region, slightly to the right of the body’s midline. It marks the precise boundary where the stomach terminates and connects directly to the duodenum, the first, short, C-shaped segment of the small intestine. This position allows the pylorus to govern the transit of material from the highly acidic stomach environment into the more delicate environment of the intestine.
Structural Components of the Pylorus
The pylorus is anatomically and functionally divided into three distinct parts. The Pyloric Antrum is a wider, funnel-shaped area that connects the main body of the stomach to the terminal section. The antrum functions as a mixing chamber, where stomach contractions push the liquified food toward the exit.
Following the antrum is the Pyloric Canal, a short, narrow passage leading directly to the opening into the small intestine. The third component is the Pyloric Sphincter, a strong, thickened ring of smooth muscle that encircles the end of the canal. This sphincter muscle is responsible for physically opening and closing the passage between the stomach and the duodenum. In an adult, the circular muscle layer forming this sphincter can be up to 8 millimeters thick, reflecting its strength.
The Primary Role of Gastric Emptying
The function of the pylorus is to regulate gastric emptying, which is the measured release of chyme (partially digested food) into the small intestine. The sphincter remains tightly closed most of the time, only opening intermittently to allow small amounts to pass through. During strong stomach contractions, only a small volume, typically around 3 milliliters of chyme, is squirted into the duodenum.
This slow release mechanism is necessary because the chyme is highly acidic. The small intestine can only neutralize and process it effectively in small, manageable batches. The slow transit allows the pancreas to secrete bicarbonate, a base that neutralizes the stomach acid, preventing damage to the intestinal lining.
The pylorus also acts as a filter, allowing only liquids and very small particles to pass, while retaining larger, undigested food particles for further breakdown. Signals from the duodenum, such as the presence of fat, acid, or high osmolarity, cause the sphincter to contract and remain closed. This controlled, one-way transit also prevents the backflow of intestinal contents into the stomach.