Joining the various sections of the digestive tract, there are placed openings called valves. Thesevalves of the digestive system control the flow of food material from mouth to the intestine.
Cardia Valve:
The cardia valve is at the entrance to the stomach, a part of the upper digestive tract. Its major function is to prevent food from being regurgitated into the esophagus from the stomach and it regulates somewhat the rate at which the food is allowed to enter the stomach. In case of dysfunction of this valve, food may regurgitate from stomach into esophagus causing symptoms like heartburn and epigastric pain.
Pyloric Valve:
The pylorus is at the exit of the stomach. This is the most important of all the valves. It must function with precision, allowing those parts of a meal that are ready for the intestinal digestive process to escape into the intestine and retaining those which are not ready to be thus passed along.
The operation of this pyloric valve is a complicated arrangement. It appears to have a delicate sense of touch, for it will closeinstantly when a piece of solid food touches it, but will allow liquid or soft foods to pass promptly. When all of the liquid portions of a meal have been separated off from an insoluble solid and out of the stomach, the contractions of the valve increase and it then becomes necessary for the peristaltic waves in the stomach to increase in strength in order to force the food mass through. In addition to this apparent sense of touch, it seems also to react to chemical changes.
An increase of stomach acid over the normal will tend to keep it closed. Fats and foods fried in fats have this same effect. This provides a longer stay in the stomach for such foods so that the fat may be dissolved by the stomach digestion in order that the oils be set free from the fat cells for saponification and absorption in the intestines. The pyloric valve is also under control of nervous reflexes from sections of the gastrointestinal tube farther along, thus preventing too large a quantity of food from being thrown into the intestine before it has finished with its work of converting and assimilating its contents.
Ileocecal Valve:
The next valve is the ileocecal valve. This is the opening between the small intestine and the colon. The opening and closing of this valve is largely under reflex nerve control. It thus reciprocates with the pyloric valve.
The last valve of the digestive tract is the anus. This valve is under the conscious and subconscious control of the brain.