Esophagus – Tutorial
Please read Unit 10 – Introduction to Digestive System Tissues and study the image slider of the four major layers of the digestive tract wall prior to completing the activities in this chapter.
Introduction to the Esophagus
The esophagus is a muscular tube approximately two centimeters (0.8 inch) in diameter that extends continuously from the inferior pharynx (throat) to the stomach. The esophagus runs directly posterior and parallel to the trachea as it descends through the mediastinum to the point where it penetrates the diaphragm at the esophageal hiatus and empties into the stomach.
When food is swallowed, peristaltic contractions of muscles in the wall of the esophagus actively push food along the lumen of the esophagus toward the stomach. The muscularis externa of the esophagus wall contains a mixture of skeletal and smooth muscle with upper (superior) regions containing primarily skeletal muscle fibers. The proportion of skeletal muscle fibers progressively decreases and smooth muscle progressively increases toward the lower (inferior) regions of the esophagus. A weak sphincter muscle known as the lower esophageal sphincter (cardiac sphincter) is normally in a state of contraction at the inferior end of the esophagus to prevent reflux of stomach contents up into the inferior esophagus. When food approaches the bottom of the esophagus, temporary relaxation of the lower esophageal sphincter allows a bolus of food to pass from the esophagus into the lumen of the stomach.
The lumen of the esophagus is lined with nonkeratinized stratified squamous epithelium. The densely packed dead cells near the apical surface of the endothelium protect the wall of the esophagus from exposure to pathogens, chemicals, and friction caused by solid foods sliding through the lumen. The submucosa of the esophagus contains esophageal glands that secrete mucus into the lumen of the esophagus which helps keep the endothelium moist and reduces friction between food and the lining of the esophagus.
Tutorial: Use the image slider below to learn more about the structure and characteristics of the esophagus.
Microscopy: Use the image slider below to learn how to use a microscope to study the esophagus on a microscope slide.
Tutorial: Use the hotspot image below to learn more about the structure and function of the esophagus.
