Structurally, the UES is 0.5-1 cm long at birth and increases in length to 3 cm in the adult. In general, the UES corresponds to the cricopharyngeus muscle, the inferior pharyngeal constrictor, and the muscle of the proximal esophagus. Surgical myotomy of the cricopharyngeus does not abolish UES tone. 7 UES location can be determined by side-port catheters for the purpose of placing proximal esophageal pH electrodes. 3 Primary peristalsis begins after swallowing, in coordination with pharyngeal contraction and UES and LES relaxation.
Secondary peristalsis occurs secondary to intraluminal distention, usually by the food bolus.
This function is important in esophageal clearance of material such as refluxed gastric contents. Tertiary contractions consist of random, spontaneous contractions that have no peristaltic function. Pressures within the esophageal body vary with respiration. The velocity of esophageal contractions is typically from 2 to 5 cm per second but is slower during the first week of life, ranging from 0.8 to 2 cm per second. The LES is the high-pressure zone between the esophageal body and the stomach.