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Role of Pyloric Sphincter

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The pyloric sphincter is a smooth muscle that acts as a valve connecting the stomach and the small intestine.

Medically reviewed by

Dr. Ghulam Fareed

Published At March 29, 2023
Reviewed AtAugust 21, 2023

Introduction

The end portion of the stomach is called the pylorus, and the beginning of the small intestine is called the duodenum. The pyloric sphincter is a smooth muscle that acts as a valve connecting the pylorus and the duodenum. It regulates the passage of partly digested food particles from the stomach to the duodenum. It also controls the backward flow of the matter back to the stomach.

What Is the Role of Pyloric Sphincter?

The pyloric sphincter regulates the passage of partly digested food from the pylorus to the duodenum. It also controls the backward flow of partly digested food and digestive juices from the small intestine to the stomach. The peristaltic movement controls the opening and closing of the pyloric sphincter. Peristalsis is the wave-like movement that allows the movement of food through the digestive system. When at rest, the pyloric sphincter remains open partly to allow water to flow to the duodenum freely. But when food is present, it closes completely to prevent the backward flow of food and to allow digestion.

Where Is the Location of Pyloric Sphincter?

The cardia, the fundus, the body of the stomach, and the pylorus are the four sections of the human stomach. The area between the esophagus to the start of the stomach is called cardia. The upper part of the stomach is called the fundus. Most of the initial digestion happens in the body of the stomach. The pylorus is at the base. It is funnel-shaped and narrows down to about 1cm in diameter. The pyloric sphincter is located at the end of the pylorus and the duodenum, which is the beginning of the small intestine.

How Is the Opening and Closing of the Pyloric Sphincter Regulated?

A series of physiological signals initiate the opening and closing of the pyloric sphincter. These signals originate either from the stomach or from the duodenum.

  • Gastric Factors: The gastric factors regulating the opening and closing of the pyloric sphincter include:

  1. Basic Electrical Rhythm (BER): There are a group of cells in the fundus that stimulate basic electrical rhythm. It consists of slow depolarization that moves along the stomach entirely. During digestion, the basic electrical rhythm creates an action potential in the smooth muscles to produce peristaltic movement to mix the food and the digestive juices properly. These partially digested food particles are called chyme. The chyme is pushed to the pylorus due to the peristaltic movements. It then forces the pyloric sphincter to open to allow the passage of the chyme to the duodenum. The chyme is passed in small sizes at a time to the duodenum.

  2. The Volume of Food: The opening and closing of the pyloric sphincter is also regulated by the amount of food in the stomach. When a lot of food is present in the stomach, it stretches the stomach walls. This creates strong peristaltic waves that prevent the pyloric sphincter from closing abruptly. This facilitates larger amounts of chyme to enter the duodenum.

  3. Hormones: Certain foods trigger hormones that can cause emptying faster. For example, meat consumption can trigger gastrin to fasten the opening of the pyloric sphincter.

  4. The pH of Chyme: When the pH of the chyme is acidic, it triggers the pyloric sphincter to open, allowing the passage of chyme to the duodenum. After the chyme passes to the duodenum, the acidity increases, which stimulates the pyloric sphincter to close.

  5. Osmotic Pressure: When the osmotic pressure in the stomach increases, it causes the passage of the chyme to the duodenum.

  • Duodenal Factors: The duodenal factors causing the opening and closing of the pyloric sphincter are;

  1. Acidity: When the acidity of the duodenum is high, the pyloric sphincter is stimulated to close to prevent the backward flow of the contents to the stomach.

  2. Fats And Proteins: When the duodenum has contents rich in fats or proteins, the pyloric sphincter is stimulated to close to prevent the contents to re-enter the stomach.

  3. Enterogastrones: Enterogastrones are hormones that regulate the opening of the pyloric sphincter and cause the mixing of the chyme.

What Are the Conditions in Which the Pyloric Sphincter Does Not Function Properly?

The conditions where the pyloric sphincter does not function properly may include:

  1. Pyloric Stenosis: When the pyloric valve becomes very thick or abnormally large, it limits the entry of chyme to the stomach. This condition is termed pyloric stenosis. This condition is mostly seen in newborns and hence also called infantile hyperplastic pyloric stenosis. Projectile vomiting after feeding that may or may not contain traces of blood is the characteristic feature of this condition. (When the body expels the ingested food at a high force, it is called projectile vomiting. It is involuntary and may land a few feet away from the person who vomits). The child may show weight loss and malnourishment. The cause of pyloric stenosis is yet not known clearly though it is thought to have genetic associations. Parents with a similar condition in their childhood are likelier to have children with similar conditions. A surgery called pyloroplasty is the only treatment known for this condition currently. A surgery done to widen the pylorus is called pyloroplasty.

  2. Pylorospasm: When the muscles of the pylorus contract prematurely and fail to relax, the condition is called pylorospasm. This can lead to inflammation. This causes obstruction of chyme flow to the duodenum leading to abdominal pain and vomiting after eating. The condition can be treated with muscle-relaxing drugs.

  3. Bile Reflux: When the bile flows back to the stomach or the esophagus, the condition is called bile reflux (bile is a digestive juice that helps in the digestion of fats). This usually happens when the pyloric sphincter fails to function properly. The condition is characterized by upper abdominal pain, heartburn, nausea, weight loss, etc. It is treated by medicines like proton pump inhibitors.

  4. Gastroparesis: A condition in which the contents are not emptied from the stomach is called gastroparesis. In such people, the peristaltic movement will be less. Dietary changes and lifestyle modifications help manage this condition.

Conclusion

The pyloric sphincter is a muscle that connects the pylorus and the duodenum. It regulates the passage of chyme from the stomach to the duodenum. It also prevents the backward flow of the chyme back to the stomach. Many factors regulate the opening and closing of the pyloric sphincter.

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Dr. Ghulam Fareed
Dr. Ghulam Fareed

Medical Gastroenterology

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