Swallowing

Swallowing, also called deglutition or inglutition in scientific and medical contexts, is a physical process of an animal's digestive tract (e.g. that of a human body) that allows for an ingested substance (typically food) to pass from the mouth to the pharynx and then into the esophagus. In colloquial English, the term "swallowing" is also used to describe the action of gulping, i.e. taking in a large mouthful of food without any biting.

Swallowing is performed by an initial push from back part of the tongue (with the tongue tip contacting the hard palate for mechanical anchorage) and subsequent coordinated contractions of the pharyngeal muscles. The portion of food, drink and/or other material (e.g. mucus, secretions and medications) that moves into the gullet in one swallow is called a bolus, which is then propelled through to the stomach for further digestion by autonomic peristalsis of the esophagus.

Swallowing is an important part of eating and drinking. If the process fails and the bolus to be swallowed mistakenly goes into the trachea, then choking or pulmonary aspiration can occur. In the human body, such incidents are prevented by an automatic trapdoor-like inversion of the epiglottis to temporarily cover the larynx and close off the upper airway, controlled by a complex reflex that facilitates the elevation of the hyoid bone and thyroid cartilage at the same time. The body will also initiate a cough reflex to expel any unwanted material that have accidentally entered the airway. A separate gag reflex, which involves the elevation of the uvula and tightening of the soft palate, prevents food from wrongly entering the nasal cavity above during swallowing.

Swallowing comes so easily to most people that the process rarely prompts much thought. However, from the viewpoints of physiology, of speech–language pathology, and of health care for people with difficulty in swallowing (dysphagia), it is an interesting topic with extensive scientific literature.

Eating and swallowing are complex neuromuscular activities consisting essentially of three phases, an oral, pharyngeal and esophageal phase. Each phase is controlled by a different neurological mechanism. The oral phase, which is entirely voluntary, is mainly controlled by the medial temporal lobes and limbic system of the cerebral cortex with contributions from the motor cortex and other cortical areas. The pharyngeal swallow is started by the oral phase and subsequently is coordinated by the swallowing center on the medulla oblongata and pons. The reflex is initiated by touch receptors in the pharynx as a bolus of food is pushed to the back of the mouth by the tongue, or by stimulation of the palate (palatal reflex).

Swallowing is a complex mechanism using both skeletal muscle (tongue) and smooth muscles of the pharynx and esophagus. The autonomic nervous system (ANS) coordinates this process in the pharyngeal and esophageal phases.

Prior to the following stages of the oral phase, the mandible depresses and the lips abduct to allow food or liquid to enter the oral cavity. Upon entering the oral cavity, the mandible elevates and the lips adduct to assist in oral containment of the food and liquid. The following stages describe the normal and necessary actions to form the bolus, which is defined as the state of the food in which it is ready to be swallowed.

1) Moistening