Esophagus

The esophagus is a muscular tube that connects the throat (pharynx) to the stomach. It is approximately 25 cm (10 inches) long in adults and is located behind the trachea (windpipe) and in front of the spine. The esophagus is divided into three parts: the cervical esophagus (the upper part), the thoracic esophagus (the middle part), and the abdominal esophagus (the lower part that connects to the stomach). The esophagus is lined with a mucous membrane that produces mucus to help lubricate food as it passes through. The walls of the esophagus contain several layers of muscle that contract in a coordinated manner to propel food from the throat to the stomach through a process called peristalsis. At the lower end of the esophagus, there is a ring of muscle called the lower esophageal sphincter (LES) that helps prevent stomach acid and contents from flowing back up into the esophagus (acid reflux).

The histology of the esophagus consists of several layers:

Mucosa: The innermost layer, which is lined with stratified squamous epithelium that protects against mechanical stress from food passage.
Epithelium: Stratified squamous epithelium that provides a protective barrier.
Lamina propria: A layer of connective tissue that contains blood vessels, lymphatics, and immune cells.
Muscularis mucosae: A thin layer of smooth muscle that helps with local movements of the mucosa.
Submucosa: A layer of connective tissue that contains blood vessels, nerves, and glands that produce mucus to lubricate the esophagus.
Muscularis externa: A layer of muscle responsible for peristalsis. The upper third of the esophagus contains skeletal muscle, the middle third contains a mix of skeletal and smooth muscle, and the lower third contains smooth muscle.
Adventitia: The outermost layer, which is made up of connective tissue that anchors the esophagus to surrounding structures.