Esophageal motility

When we eat, food enters the mouth where it is chewed up by the teeth into a smaller, soft mass called the food bolus.

The bolus is then pushed by the tongue into the pharynx and continuous to travel down through the esophagus, squeezed by an involuntary movement called peristalsis, until it reaches the stomach.

So, the esophagus is a muscular tube that runs vertically downwards and carries food from the pharynx to the stomach. In an adult it’s about 25 cm long and can be divided into three regions.

First is the cervical region, where it connects with the pharynx behind the trachea.

Separating the pharynx and the cervical region of the esophagus is the upper esophageal sphincter, which is a muscular ring that contracts and relaxes to control the entrance of food into the esophagus.

Below the cervical region is the thoracic region, that begins at the level of the suprasternal notch and ends when the esophagus goes through the diaphragm via an opening called the esophageal hiatus.

And finally there's the abdominal region, which starts at the esophageal hiatus and ends where the esophagus connects to the stomach.

Separating the abdominal region and the stomach is the lower esophageal sphincter, also known as the gastroesophageal sphincter, which relaxes to let food into the stomach.

Now, because most of the esophagus is located inside the thorax, the intraesophageal pressure is equal to the intrathoracic pressure, and both of these pressures are lower than abdominal pressure. This means that food in the esophagus gets pulled towards the area with lower pressure - a bit like how dirt gets pulled into a vacuum.

So, the upper and lower esophageal sphincters have to stay contracted to prevent air from entering the digestive tract and altering this pressure gradient.

In addition, the lower esophageal sphincter also prevents stomach acids from entering the esophagus.

The esophagus receives most of its nerve supply from two sources - there’s extrinsic innervation by the vagus nerve, or cranial nerve 10, and there’s also an intrinsic plexus of neurons located inside the walls of the esophagus, called the enteric nervous system.