Deglutition

Swallowing, otherwise known as deglutition, facilitates the transport of food from the mouth to the stomach. It is a multifaceted process that involves both the tongue and the muscles of the throat and esophagus. Saliva and mucus aid in this process, which takes approximately 4 to 8 seconds for semi-solid or solid food and around 1 second for liquids or very soft food.

Swallowing can be divided into three stages: the voluntary phase, the pharyngeal phase, and the esophageal phase. Although the voluntary phase is under your control, the latter two are managed by the autonomic nervous system.

During the voluntary phase, chewing is finished, and the swallowing process begins. The tongue moves backward and upward against the palate, propelling the food to the rear of the oral cavity and into the throat. Other muscles help keep the mouth shut and prevent the food from slipping out.

The pharyngeal phase is initiated next, with receptors in the throat sending impulses to the swallowing center in the medulla oblongata. The uvula and soft palate then move upward, blocking off the nasopharynx, while the epiglottis prevents food from entering the windpipe. Breathing halts momentarily during deglutition. The food is then moved through the throat and into the esophagus via the relaxation of the upper esophageal sphincter.

The esophageal phase marks the final stage of swallowing and the commencement of peristalsis, controlled by the medulla oblongata. The bolus is transported through the esophagus and towards the stomach via peristalsis. The muscularis' circular muscle layer contracts, forcing the food distally. Simultaneously, the muscularis' longitudinal muscle layer also contracts, expanding to receive the food. As the food approaches the stomach, the esophagus expands, triggering a short reflex that relaxes the lower esophageal sphincter, allowing the food to enter the stomach. The mucus secreted by the esophagus lubricates the food and reduces friction during this final phase.