Posted on 18 Feb 2011 15:07
The esophagus is part of the gastrointestinal tract, or alimentary canal, of the digestive system.
It is a straight, collapsible muscular tube in the neck which connects the pharynx to the stomach, passing through the diaphragm.
Approximately 10 inches (25 cm) in length, the esophagus carries food, liquids and saliva from the mouth to the stomach.
The esophagus is made up of four layers, the mucosa, submucosa, muscularis propria, and adventitia but has no serosa like the rest of the gastrointestinal tract.
The muscularis propria, responsible for moving food through the esophagus by muscular action, is made up of both smooth and skeletal muscle. Its upper part contains skeletal muscle. Its middle part is a mixture of skeletal and smooth muscle, and its lower, or distal part contains smooth muscle.
The proximal border of the esophagus is the upper esophageal sphincter. The tube descends through the thorax behind the trachea and passes through the mediastinum. It penetrates the diaphragm through an opening called the esophageal hiatus is continual with the stomach underneath the diaphragm in the abdominal cavity.
Where the esophagus joins the stomach there are thickened muscle fibers which contract to close the entrance to the stomach so that stomach contents are not regurgitated back into the esophagus. This band of muscle is called the lower esophageal sphincter (LES). Peristaltic waves in the esophagus, when reaching the stomach, relax these muscle fibers to open the entrance.
The Digestive System
Chewed food that is swallowed is called a bolus. It takes 4 to 8 seconds for a bolus to move down the esophagus to the stomach. If the esophagus were nothing more than a passive tube, like a piece of garden hose, the bolus could easily get stuck, even if the tube is perfectly vertical. Instead, the muscular esophagus pushes the food and fluids along by a contractions called peristalsis which cause the muscles to narrow in a wave like action down the tube. This wave, much like an ocean wave, pushes the food or fluid in front of it, down to the stomach. to the lower esophageal sphincter, which relaxes to allow the food to enter the stomach.