The esophagus is an often overlooked organ which is a vital component of your digestive system. Without it, there would be no way for food and liquids to make their way from your mouth to your stomach. It doesn't take a doctor to realize that this would not be convenient for most people.
The esophagus itself is a muscular tube, approximately 25 cm (10 inches) from top to bottom. The top of the esophagus is attached to the pharynx, which is the anatomical term for the back of your throat. The bottom of the esophagus attaches to the stomach.
There are two major muscle layers lining the esophagus. The first is an outer muscle layer, whose fibers run longitudinally up and down the length of the esophagus. The inner layer of muscle contains circular fibers which form a series of rings around the esophagus.
The esophagus is a somewhat unique organ in that the muscle in the upper part is under voluntary control, while the muscles of the lower end are controlled involuntarily. The upper portion of both muscle layers are made up of striated muscle, which you are able to contract voluntarily when you swallow. As you proceed down the length of the esophagus, the muscle fibers gradually change to a type of muscle known as smooth muscle. By the time you reach the lower esophagus, all of the muscle has become smooth muscle. Smooth muscle is under in voluntary control by your nervous system. These muscles and then merge with the muscles in the stomach.
The esophagus joins to the stomach just below the diaphragm. The diaphragm is the large muscle, located at the base of your lungs which aids in breathing. There is a hole in the diaphragm through which the esophagus passes.
At the top and the bottom of the esophagus are a pair of sphincters. Sphincters are valves found throughout the body which selectively block or allow other substances to pass through. The upper esophageal sphincter is normally closed. It opens for a brief period when you attempt to swallow either solid food or liquids. When the upper esophageal sphincter opens, it blocks the airway going to the lung. This prevents the food or liquid from passing in to your lungs. It goes without saying that pouring food in to your lungs would not be good for your health.
The lower esophageal sphincter connects the esophagus to the stomach. Even at rest, this sphincter is tightly closed. This prevents the contents of the stomach from flowing back into the esophagus. The contents of the stomach are highly acidic and if they were to flow back into the esophagus, they would cause much irritation and damage to the delicate tissues in the esophageal lining.
As you swallow, the piece of food you are eating is moved from the mouth to the pharynx voluntarily. As this takes place, the upper esophageal sphincter immediately relaxes and allows food into the upper esophagus. This sequence stimulates a series of muscle contractions known as a peristaltic wave. The peristaltic wave is a coordinated series of muscle contractions which began in the upper esophagus and slowly pushes the food down in to the stomach.
Contrary to popular belief, food does not get to the stomach by gravity. This can be demonstrated by standing on your head and attempting to swallow food or water. This can be done, although from time to time gravity will override the strength of the muscles in the esophagus and you will end up spitting food all over your own face.
Once the food has reached the bottom of the esophagus, the lower esophageal sphincter relaxes, allowing the food to enter the stomach.
There are some common conditions related to esophageal dysfunction. The most common of these is an abnormal relaxation of the lower esophageal sphincter. This causes contents of the stomach to regurgitate back into the esophagus. This condition is commonly known as gastroesophageal reflux disorder, or GERD.