How You Swallow

The swallow mechanism is normally broken down into three phases. The oral phase involves chewing and formation of the bolus (term used to describe a “packet” of food or liquid) and propulsion of the bolus to the pharynx or throat (Figure 1 - see below). The pharyngeal phase involves transfer of the bolus past the larynx and into the esophagus (Figure 2- see below). The esophageal phase involves transport of the bolus through the esophagus and into the stomach (Figure 3- see below).

During the oral phase, the lips, teeth, tongue, and jaw muscles mix the food with saliva to create the proper consistency for ingestion. Once the bolus is formed in the oral cavity it is propelled into the oropharynx by the tongue; this completes the oral phase of swallowing.

Once the bolus reaches the tonsils, it triggers the pharyngeal phase of the swallowing reflex. This phase of the swallow mechanism is completely automatic (there is no ability to consciously control this). The entire pharyngeal phase of the swallow lasts approximately one second. In this phase of the swallow, several events are occurring in rapid secession:

1. The palate closes against the back wall of the throat separating the oral cavity from the nasal cavity. This action prevents food or liquid from coming up through the nose
2. The vocal cords close. This shuts off access to the trachea.
3. The throat muscles constrict. This occurs in a coordinated manner to help push the food downwards towards the esophagus.
4. The larynx is pulled upwards and forwards. During this, the epiglottis tilts posteriorly, covering and protecting the vocal cords. The bolus is also directed to the sides by the shape of the epiglottis.
5. The upper esophageal sphincter (muscle that controls entry of food or liquid into the esophagus) relaxes. This allows the bolus to enter the esophagus.

The final phase of the swallow is the esophageal phase. Once the food bolus enters the esophagus, it is actively transported down to the stomach. Swallowing is complete when the bolus passes the lower esophageal sphincter and into the stomach.

Problems in any of the phases of the swallow reflex can cause dysphagia and aspiration. In the oral phase, poor bolus formation can lead to poor handling of the food during the pharyngeal phase and possible spillage into the trachea. As alluded to above, the pharyngeal phase is very complex, and there are many potential difficulties during this phase of the swallow. Delayed onset of the swallow can lead to poor initiation of the pharyngeal phase; this occurs fairly commonly in the elderly population. Poor throat sensation can lead to premature spillage of the food bolus into the trachea. Similarly, incoordination or weakness of the throat muscles can lead to aspiration. While the esophageal phase is often ignored by many in the evaluation, problems during this phase can lead to many dysphagia complaints including a feeling of food sticking within the chest or regurgitation. Frequently encountered problems during this phase include Zenker’s diverticulum. and esophageal stricture (narrowing of the esophagus due to scarring). The doctors at NYU Voice Center, under the direction of Dr. Milan Amin, provide expert evaluation and treatment of swallowing problems.