What process does cardiac sphincter open involuntary?

The cardiac sphincter, also known as the lower esophageal sphincter (LES), opens involuntarily during the process of swallowing, also known as deglutition. Deglutition is a complex physiological process that involves several coordinated muscle contractions and relaxations to propel food or liquid from the mouth into the stomach.

During swallowing, the relaxation of the cardiac sphincter is crucial for allowing food or liquid to pass from the esophagus into the stomach. This relaxation is triggered by a combination of neural and hormonal mechanisms:

1. Neural Mechanisms: When you swallow, the brain sends signals through the vagus nerve, a major nerve that controls various functions in the digestive system. The vagus nerve stimulates the release of neurotransmitters, such as acetylcholine, which cause the muscles of the cardiac sphincter to relax and open.

2. Hormonal Mechanisms: The hormone gastrin also plays a role in relaxing the cardiac sphincter during swallowing. Gastrin is released by the stomach in response to the presence of food or liquid. It acts on receptors in the smooth muscle of the sphincter, causing relaxation and allowing food to pass into the stomach.

Therefore, the cardiac sphincter opens involuntarily during swallowing due to the coordinated actions of neural and hormonal mechanisms that ensure the efficient passage of food or liquid into the stomach.