Anatomically and functionally, the esophagus is the least complex section of the digestive tube. Its role in digestion is simple: to convey food from the pharynx (the throat) to the stomach.
In its role as the first conduit in the digestive tube, the esophagus is routinely exposed to rough and abrasive foodstuffs, like fragments of bone, fibrous plant leaves and frozen ice. Its surface should therefore be resistant to trauma, and indeed, the esophagus is lined with a type of tissue know as stratified squamous epithelium, one of the toughest tissues in the human body.
The strategic position of two one-way valves (sphincters) directs food in a one-way path down the esophagus. The upper esophageal sphincter relaxes to let food enter the esophagus. The lower esophageal sphincter, a strong ring of muscles at the bottom, relaxes momentarily to allow food to pass into the stomach.
The esophagus receives nerve supply by the vagus nerve and sympathetic divisions of the nervous system: vagal activity increases esophageal activity. Swallowing is triggered by a signal transmitted by the vagus nerve. The timing of the swallowing sequence (primary peristalsis) is dependent on nerves intrinsic (belonging to) to the esophagus.
The esophagus is a muscular tube about nine and a half inches long, that is lined with soft moist tissue, called mucosa. This mucosa is pink and moist and appears very much like the inside of our cheek. The mucosa, which lines the esophagus and most of the digestive tract, allows for easy movement of food through the tract. It also helps to protect the digestive tract from the acids and enzymes that are produced to convert food into small molecules.
This picture is an image of the middle of the esophagus. It has a wide open tubular appearance and pink coloration. Seconds after this picture was taken, a contraction occurred. These normal sweeping wavelike contractions are what move food and liquid from the mouth to the stomach.
These are images of the end of the esophagus. There is a specialized muscle here which acts like a valve and which is called the lower esophageal sphincter. It remains closed most of the time, only opening to allow swallowed food and liquid to be swept through into the stomach. When you belch, the air pressure in the stomach overcomes the pressure of the valve and the air you have swallowed bursts up the esophagus past this valve. The Lower Esophageal Sphincter in Image 1 is closed while that in Image 2 is open. Gastroesophageal reflux occurs when the stomach's contents back up into the esophagus. View an animation of gastroesophageal reflex here.
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Image 1 - Closed Esophageal Sphincter |
Image 2 - Closed Esophageal Sphincter |
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The larynx or voice box, although not actually part of the digestive system, looks like the picture on the right. This is looking from above. You notice the vocal cords on each side. These move back and forth as air is forced out over the cords. Amazingly, these simple fibrous bands of tissue allow us to talk, whisper, shout and sing the entire range of melodious and rich bass tones. This is a normal appearance of the larynx. |
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The Human Body
Normal Images of the Esophagus
The Larynx
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