It is a small constriction at the lower end of the stomach that directly opens into the duodenum. The aperture generally marks the end of the stomach and the beginning of the small intestine. It is often mistaken as keratosis pilaris, a common, autosomal dominant condition marked by rough, red, bumps on the skin.
As aforementioned, the passage is located in the upper abdomen.
It is a cone-shaped structure covered with a mucous-membrane lining that consists of the following parts:
- Pyloric antrum: It is the first section of the pyloric part of the stomach that closes partially or completely from the remainder of the gastrointestinal tract during digestion. It is bulgy and connects to the body of the stomach. A small groove demarcates it from the second part of the aperture.
- Pyloric canal: This narrow, tubular portion of the stomach ends at the gastroduodenal junction.
At the end of the opening between the stomach and the small intestine, there is a compact ring of smooth muscle or valve, called pyloric sphincter. Thickening of the lower region of the pyloric canal gives rise to this structure. It clearly separates the stomach from the duodenum by closing the natural orifice whenever required. The pyloric valve is innervated by sympathetic nerve called celiac ganglion in the upper abdomen.
The inner surface of the aperture is lined with gastric mucosa, which secretes gastric juices to promote digestion. The mucosa is normally covered with thick mucus secreted by the columnar epithelial cells. It chiefly serves the following two purposes:
- Lubrication of food masses in order to facilitate movement within the stomach
- Formation of a protective layer over the lining epithelium
The primary function of the cone-shaped constriction is to prevent regurgitation of food from the small intestine. It also aids in the proper movement of the undigested food through the intestinal tract. The pyloric sphincter opens periodically to permit small quantities of well-emulsified food to enter the duodenum. Once the duodenal region is completely filled, the pyloric valve contracts and shuts off due to increase in pressure. The food is pushed deeper into the remaining portions of the intestine with the help of peristaltic waves in the duodenum.
The small circular opening is often affected with pyloric stenosis. In this condition, the aperture undergoes narrowing due to progressive thickening of the pyloric canal, causing uncontrollable vomiting and abdominal pain. Presence of tumors in the pyloric canal can also block the aperture and cause severe discomfort. Pancreaticoduodenectomy/
In some instances, the conical passage may remain in a patulous/open state to allow the passage of food into the intestine before the completion of gastric digestion. This occurs due to pyloric spasm in which the sphincter undergoes a sudden, involuntary contraction. A deformed aperture can also be the cause of acid reflux. Helicobacter pylorus (H. pylori) is a bacterium that causes chronic inflammation of the inner lining of the stomach and subsequent formation of ulcers. A broad spectrum of antibiotics is needed to treat this condition.
Pictures of Pylorus