GI Competency Course Esophagus Anatomy and Physiology of the Esophagus
  • This is actually the third organ of digestion, coming after the mouth and pharynx.
  • It is a hollow, muscular tube approximately 23-25 cm long, and 2-3 cm wide.
  • Its function is to deliver food to the stomach.
  • The wall of the esophagus are composed of three layers: the mucosa, submucosa, and muscularis. Most of the other structures in the GI tract have four layers, but the esophagus is missing the serosa.
  • The cells lining the esophagus are composed of stratified squamous epithelium.
  • The muscle layers of the esophagus for the first five percent are striated muscle, the next 35-40% are a combination of striated and smooth muscle, while the final 50-65% is smooth muscle only.
  • The Upper Esophageal Sphincter (UES) protects food from entering the lungs and is composed of cricopharyngeal muscle.
  • The Lower Esophageal Sphincter (LES) (Cardiac Sphincter) controls the passage of food into the stomach.
  • It is approximately 2-4 cm, but in truth is not an anatomical marking, but a physiological sphincter.
  • The esophagus is supplied by both sympathetic and parasympathetic nerves, including the Vagus nerve, which supplies the striated muscle to the upper part of the esophagus.
  • When you are resting, both UES and LES are closed.
  • Once you swallow, the UES opens to allow the food through, and gravity, peristalsis, and the bolus of food push the food down the esophagus. As the striated muscles contract, the LES opens up to allow the food to enter. The whole process travels at approximately 3-5 cm/sec. As the bolus passes into the stomach, the LES closes, preventing reflux.
  • Food passes with the assistance of gravity, and the actual bolus of food or liquid, but most of the process is through the contraction of muscles progressing from the upper to lower esophagus called peristalsis.
  • If it is initiated by a swallow, it is termed “primary peristalsis”.
  • It is possible for the whole bolus not to pass the first time, and to have food/liquid remaining in the esophagus.
  • The esophagus will then contract to clear it, without any swallowing movement.
  • This is termed “secondary peristalsis”.