MedlinePlus explains that food travels from the mouth to the stomach through the esophagus and that a "**ring of muscle fibers in the lower esophagus prevents swallowed food from moving back up**." It notes: "These muscle fibers are called the **lower esophageal sphincter (LES)**. **When this ring of muscle does not close all the way, stomach contents can leak backward into the esophagus**." This description shows that normally the LES is closed at rest and must relax to allow contents to pass, reinforcing that transit across the sphincter is not due to passive dripping.

The esophagus carries food and liquid from your mouth to your stomach. At the opening of your upper esophagus, the upper esophageal sphincter stays closed when there’s no food or liquid in sight. At the lower esophagus, the lower esophageal sphincter usually stays shut when no food or liquid is coming its way to prevent stomach contents from getting into your esophagus.

In this human manometry/fluoroscopy study, the authors report that “Sensory stimuli originating from the pharynx **inhibit esophageal peristalsis induced by a dry swallow.** … In all subjects progression of peristalsis induced by swallowing of different volumes of water and mashed potato boluses was **inhibited at all sites by pharyngeal water injection.** Pharyngeal water injection invariably **halted transit of the barium boluses through the esophagus.**” The conclusion states that “Sensory impulses originating from the pharynx 1) **inhibit esophageal bolus transit** and 2) are capable of overcoming the facilitating effect of a liquid bolus on the swallowing apparatus.”

The upper esophageal sphincter opening is necessary for bolus passage from the pharynx into the esophagus, and the UES is tonically contracted at rest. During swallowing, there is inhibition of the contraction leading to almost zero pressure as the pharyngeal muscles send the bolus from the pharynx into the esophagus.

The upper esophageal sphincter (UES), which controls the entry of a food bolus, is found at the proximal extent of the cervical esophagus. After the food bolus transits the UES, the pressure immediately increases to twice resting pressure to prevent reflux, before gradually returning to baseline. The lower esophageal sphincter (LES) is not as anatomically distinct as the UES and is composed of thickening of the circular esophageal fibers near the gastroesophageal junction. It generates a resting pressure of 14–34 mmHg. The body of the esophagus is not tonically contracted and relies on peristaltic contractions to propel food down its length.

The decision tree selects one of twelve possible mechanical states, based on: whether the diameter is open or closed, whether the diameter (if open) is constant, increasing or decreasing, and whether the wall is in active contraction, relaxation or passive. These states can describe the lumen as open or closed at different locations and times during peristalsis. The method shows that the esophageal body alternates between open (distended) and closed states as a bolus is propelled, rather than remaining permanently open or closed.

During swallowing, food passes from the mouth through the pharynx into the esophagus and then into the stomach. A ringlike band of muscle, called the upper esophageal sphincter, opens to allow food to enter the esophagus and then closes to prevent backflow into the throat. Another band of muscle at the lower end of the esophagus, the lower esophageal sphincter, relaxes to let food pass into the stomach and then tightens again to prevent stomach contents from flowing back up.

Normally, the upper esophageal sphincter relaxes to allow food and liquid to enter the esophagus and then closes. Coordinated, wave-like muscle contractions (peristalsis) move the food down the esophagus. At the lower end, the lower esophageal sphincter opens so that food can enter the stomach and then closes again. The esophagus itself is a muscular tube that collapses when empty and opens only to accommodate a passing bolus.

The provincial health resource explains that "normally, the **muscles in your throat and esophagus squeeze, or contract, to move food and liquids from your mouth to your stomach without problems**." It then contrasts this with conditions where these muscles or nerves do not work properly. This description emphasizes that **active muscular squeezing** is the usual mechanism for moving liquids through the esophagus, not passive dripping through a static, sealed tube.

The esophageal sphincters are bands of muscles at the top and bottom of the esophagus. The top sphincter prevents air from flowing into the esophagus while breathing, and the bottom sphincter prevents food from flowing back up the esophagus. The upper sphincter is usually closed when a person is not eating, and the lower sphincter opens to allow food to flow into the stomach.

In normal human physiology, the esophagus is not fully sealed shut along its entire length at rest. Instead, the upper and lower esophageal sphincters are tonically contracted most of the time, while the esophageal body is a muscular tube that can contain swallowed liquid and propel it downward by peristalsis.

In the video, the lecturer contrasts the trachea and esophagus on a diagram: "the respiratory tract, that is the trachea, is held open permanently... we're not constantly eating or swallowing so when we're not swallowing the trachea is open... but notice that the esophagus which lies posterior to it is collapsed... that's what we actually have at rest when we're not eating or swallowing." He adds: "the esophagus is collapsed and the trachea is held open permanently."

In explaining normal swallowing, the ENT specialist notes that when a swallow is initiated, "the **cricopharyngeus muscle or upper esophageal sphincter relaxes and opens to allow food and liquids to pass into the esophagus**." Afterwards, "**the cricopharyngeus muscle closes back up** to prevent any regurgitation back up into the throat." This clinical description shows that entry into the esophagus depends on sphincter relaxation during a swallow, and that the sphincter is otherwise closed, rather than being an open channel that allows constant passive flow.

The lower esophageal sphincter remains closed the majority of the time, only opening to let food through to the stomach or to regurgitate stomach gas. When the LES fails to close, it allows stomach acid to splash up from the stomach into the esophagus.