Esophageal motility

Definitions & Key takeaways

The esophagus is a muscular tube that extends from the pharynx to the stomach. Thanks to its motility, food and liquids move down after swallowing from the pharynx to the stomach. The muscle in the wall of the esophagus moves food and liquid forward by squeezing and pushing them along, the process called peristalsis. Factors that affect esophageal motility include age, smoking, caffeine, alcohol, and spicy foods. Disorders of esophageal motility can lead to problems such as difficulty swallowing (dysphagia), chest pain, or heartburn (gastroesophageal reflux disease).

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Introduction0:00–0:21

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.

Anatomy0:21–3:56

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 a 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 through 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.
Now, if we take a closer look at a cross-section, we can see that like other parts of the gastrointestinal tract, the esophagus has 4 layers.
The outermost layer is the adventitia, a thick fibrous connective tissue that differs from the serosa, which is the slippery serous membrane that surrounds the walls of the stomach and intestines.
Next, is the muscularis externa, composed of an outer longitudinal layer and an inner circular muscle layer that’s thicker in the upper and lower parts of the esophagus to form the esophageal sphincters.
Now, between the two muscle layers, there’s a plexus, or network of nerves, called the myenteric or Auerbach’s plexus, which help coordinate muscle contraction and relaxation.
Following the muscular layer is the submucosa, a dense layer of connective tissue that contains blood vessels, lymphatics and mucus glands that secrete mucus which travels to the lumen through ducts, and along with saliva swallowed with food, lubricate the surface to ease the passage of food downwards.
Now, buried in the submucosa, there’s also a second nerve plexus, the submucosal plexus, also called the Meissner's plexus, which helps control the size of blood vessels and secretion of mucus and together with the myenteric plexus form the enteric nervous system.
And finally, there’s the inner lining of the esophagus called the mucosa, which itself consists of three cell layers. The outermost layer is the muscularis mucosa or muscularis interna, and it’s a layer of longitudinal smooth muscle.
The middle layer is the lamina propria, which is mainly composed of connective tissue. Finally, there’s the epithelial layer that covers the inner surface of the esophagus and comes in direct contact with food.

Swallowing3:56–4:50

So, swallowing begins with the oral phase and the voluntary movement of the tongue that pushes the food bolus backwards, into the pharynx.
This starts the swallowing reflex. First, mechanoreceptors, thermoreceptors, and taste receptors in the pharynx and upper esophagus detect the food.
These receptors send afferent, sensory, information, through the trigeminal, glossopharyngeal and vagus nerve to the medulla, where there’s a region called the swallowing center that controls the involuntary phases of swallowing.
Next, the swallowing center sends efferent, motor, information, mainly through the glossopharyngeal and vagus nerves to the muscles of the pharynx and upper esophagus, and this causes the upper esophageal sphincter to relax, allowing the food bolus to pass through.
Then, the upper esophageal sphincter closes to prevent food from refluxing back into the pharynx. The swallowing reflex also triggers peristalsis which is a series of coordinated wave-like muscle contractions that helps squeeze the food bolus towards the stomach.

Peristalsis4:50–7:07

The first wave is called the primary peristaltic wave, and it begins when the bolus reaches the esophagus. So, peristalsis starts in the muscularis externa when the inner circular muscle layer in the esophagus above the bolus contracts and squeezes the bolus downwards.
At the same time, the outer longitudinal muscle layer in the part of the esophagus right below the bolus relaxes and lengthens and therefore pulls the bolus downwards.
Now, if you are swallowing when standing, or sitting, the passage of the bolus is also assisted by gravity. So, as the food is coming closer to the abdominal region and the lower esophageal sphincter, its presence is detected by mechanoreceptors and chemoreceptors located in the mucosal layer.
These receptors send afferent, sensory, information, through the vagus nerve to the medulla. Next, the medulla responds by sending efferent, information through the vagus nerve which releases the neurotransmitter vasoactive intestinal peptide or VIP within the lower esophageal sphincter.
The VIP directly inhibits the action of the inner circular muscle layer, causing the sphincter to relax so food can pass into the stomach.
Then, the lower esophageal sphincter closes to prevent food or stomach acids from refluxing back into the esophagus. However, sometimes the primary peristaltic wave is not strong enough to push all the food into the stomach.
So, the food particles left behind cause distention of the esophageal wall, which is detected by mechanoreceptors located in the mucosal layer.
These receptors send afferent, sensory, information to the enteric nervous system and the myenteric plexus. The myenteric plexus responds by coordinating muscle contractions above the site of distention and relaxation below it.
This, initiates a secondary peristaltic wave that pushes any remaining food into the stomach, much like the primary peristaltic wave.
Depending on the individual and size of the bolus, the primary peristaltic wave typically travels at around 3 centimeters per second, so with solid food it usually takes about 10 seconds to push it from the cervical region to the stomach.

Review7:07–7:43

Alright, as a quick recap, the entrance and exit of the esophagus are guarded by the upper and lower esophageal sphincters, which are usually closed to prevent air or stomach acid from entering the esophagus.
During swallowing, food in the pharynx and upper esophagus stimulates an involuntary contraction, called peristalsis. So, a primary peristaltic wave travels the esophagus and pushes food down.
But if there’s some food that remains in the esophagus, then its cleared through by a secondary peristaltic wave, which is mainly controlled by the enteric nervous system.