The esophagus is around 25 cm (10 inches) long and 1.5 to 2 cm wide. It transports food from the pharynx to the stomach (about 1 inch). The esophagus enters the stomach via the diaphragm after passing via the trachea, the heart, and in front of the spinal column.
The mucosa, submucosa, muscularis, and tunica adventitia are the esophagus' four layers. The stratified squamous epithelium that makes up the mucosa contains several mucous glands. The thick, floppy layer of fibrous tissue known as the submucosa connects the muscularis to the mucosa. The mucosa and submucosa work together to create lengthy, longitudinal folds that would give the esophagus opening a star-shaped cross section. The muscularis is made up of an exterior layer with longitudinal fibers and an inner layer with circular fibers. Both muscle groups are wrapped around and along the digestive tract, but the inner one has a very tight spiral, making the windings almost circular, while the outer one has a spiral that is progressively unwinding, making it almost longitudinal. The tunica adventitia, the esophagus' outer layer, is made up of loose fibrous tissue that joins the esophagus to nearby tissues. The esophagus is typically empty unless when swallowing, and the longitudinal folds of the mucosal and submucosal layers effectively block off the lumen, or channel, of the esophagus.
In the upper portion of the esophagus, striated (voluntary) muscle is present. The lower third is made entirely of smooth muscle, while the middle third is made up of both striated and smooth (involuntary) muscle. Two sphincters, or circular muscles, which function like drawstrings to close channels, are found in the esophagus. Other than during swallowing, both sphincters are typically closed. The level of the cricoid cartilage is where the upper esophageal sphincter is situated (a single ringlike cartilage forming the lower part of the larynx wall). The cricopharyngeus muscle is the name of this sphincter. The 3 to 4 cm of the esophagus that pass through the diaphragmatic hiatus, also known as the lower esophageal sphincter, are enclosed. Except in reaction to a descending contraction wave, when it briefly relaxes to permit the expulsion of gas (belching), the lower esophageal sphincter is kept in tension at all times. Therefore, the lower esophageal sphincter is crucial in preventing the esophagus from experiencing reflux of gastric contents in response to changes in body position or intragastric pressure.
The lower esophageal sphincter relaxes and the bolus enters the stomach when it reaches the junction with the stomach. The bolus may become halted in the middle or lower esophagus if it is too large or if the peristaltic contraction is too feeble. In this case, the bolus is propelled into the stomach by subsequent peristaltic contractions that begin surrounding it in reaction to the local esophageal wall distension.
When a beverage is ingested, how quickly it travels through the esophagus is somewhat influenced by the body's orientation and the pull of gravity. Liquids are handled similarly to solids when swallowed horizontally or head-down, with the liquid going ahead of the peristaltic contraction as it advances. (Animals with particularly long necks, like the giraffe, can carry liquids through the esophagus for many feet due to the high pressures and forceful contractions of the esophageal peristaltic wave.) However, when the body is upright, liquids enter the esophagus and travel downward by gravity to the lower end, where they remain for 8 to 10 seconds until the lower esophageal sphincter opens and the peristaltic contraction occurs, at which point they are emptied into the stomach.
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