Pyloric sphincter: Definition Location, function, Disorders
Pyloric sphincter: Definition Location, function, DisordersThe pyloric sphincter is a small piece of intestinal smooth muscle that acts as a valve and controls the flow of partially digested food from the stomach to the duodenum. The opening and closing of the sphincter are controlled by peristaltic waves generated by the stomach during the digestion process. At rest, the sphincter remains partially open to allow free circulation of water in the duodenum; however, it is immediately closed in the presence of food so that digestion can take place.
It prevents the passage of food particles from the very small intestine (duodenum) until they mix well with gastric juices.
Prevents reflux from the intestine to the stomach.
The abdominal wall is made up of three layers of smooth muscles. The outer layer is longitudinal, the middle layer is circular, and the inner layer is oblong. In the pylorus, the middle globular layer becomes too thick (50 to 100 percent thicker than the previous one) to form the pyloric sphincter.
The sphincter is tonically contracted a little most of the time. But it is usually open enough for water and other liquids to pass from the stomach to the intestine.
Sphincter constriction prevents food from emptying into the intestines until well mixed with gastric juice (which contains HCl and enzymes). This mixture gives chyme, which has an almost liquid consistency.
The pyloric sphincter also prevents the reflux of chyme from the intestine (duodenum) to the stomach.
Location of the pyloric sphincter
The human stomach is divided into four distinct sections, as shown in the following figure. The cardia is located between the esophagus and the entrance to the stomach, with the lower part being the upper part of the stomach and the main body where most of the initial digestion takes place. At the base is the pylorus, funnel-shaped and about 1 inch in diameter. The pyloric sphincter is located at the junction between the pylorus and the duodenum of the small intestine.
The function of the Pyloric Sphincter
During food intake, the stomach receives signals to start producing gastric secretions to start the digestion process. When food enters the stomach, it immediately mixes with these secretions to form a thick acidic liquid called chyme. During this time, the pyloric sphincter remains closed, while the stomach attempts an orderly mixing using peristaltic waves. One of the functions of the sphincter is to regulate the amount of chyme that is released into the duodenum, allowing maximum absorption of nutrients. Another important function of the pyloric sphincter is to inhibit the reabsorption of chyme and bile. The reproduction of chyme or bile can cause bloating and discomfort in the stomach of the patient.
Physiological Regulation of the Pyloric Sphincter
A complex network of physiological signals controls the opening and closing of the pyloric sphincter. These signals come from the stomach or duodenum.
1. In the body there is a group of cells that generate a continuous basic electrical rhythm (BER), with slow depolarizations that run throughout the abdomen. During digestion, these basic electrical rhythm waves can stimulate action potentials in smooth muscles and cause strong waves of peristalsis to mix food and gastric juices. The waves push partially digested food into the pylorus and open the pyloric sphincter to let in a few milliliters of chyme at a time.
2. The amount of food in the stomach also affects the pyloric sphincter. When present in large quantities, it dilates the walls of the stomach, which in turn produces strong peristaltic waves and prevents abrupt closure of the pyloric sphincter, allowing large amounts of chyme to enter the duodenum.
3. Certain foods trigger the release of certain hormones to increase the rate of gastric emptying. Meat promotes the release of gastrin from the gastric mucosa that triggers the opening of the pyloric sphincter. Foods high in carbohydrates increase the rate of gastric emptying, while foods high in protein promote a much slower rate, and foods high in fat cause the rate to be lower.
4. The pH of the chyme is also another regulatory factor. When there is excess acidity in the stomach, the pyloric sphincter opens, and when the acid content enters the duodenum, the level of acidity increases, and the sphincter closes immediately.
5. An increase in osmotic pressure in the stomach also causes the expulsion of chyme into the duodenum.
1. The high acidity in the duodenum and the high levels of fatty or protein products provoke an intragastric reflex that crosses the walls of the duodenum through the nerves and promotes the closure of the pyloric sphincter so that the chyme cannot enter.
2. Enterogastrones also affect the activity of the pyloric sphincter. These are hormones that promote sphincter closure and reduce bloating. Cholecystokinin (CCK) is released when there is a high level of fat in the duodenum and blocks the effect of gastrin released in the stomach. Another hormone called a gastric inhibitory peptide (GIP) can also affect you in the same way but to a lesser extent.
Pyloric Sphincter Disorders
Pyloric stenosis occurs when the sphincter muscle becomes abnormally large or thick, restricting the normal flow of chyme from the stomach. This disease occurs mainly in newborns and is called infantile hypertrophic pyloric stenosis. It is characterized by severe projectile vomiting after eating and may contain traces of blood in the vomit. The child may lose weight and experience persistent hunger and dehydration due to malnutrition. The cause of pyloric stenosis is still unknown, but scientists believe it is related to genetics. Parents who had the disease in childhood have a higher risk (20%) of having a child with the same disorder. Currently, surgery is the only option to reverse the effects of increased muscle mass. Adults are also at risk for the disease, but contractures are usually caused by cancer scars, growths, inflammation, or ulcers.
Pylorospasm occurs when the muscle fibers of the sphincter contract prematurely and do not relax, causing inflammation. This obstructs the flow of chyme to the duodenum and the stomach can become overly full, causing vomiting and pain after eating. This disorder can be treated with muscle relaxants.
Pyloric sphincter: Definition Location, function, Disorders