Updated: 03/11/08 10:36 AM
HOME HEAL EDUCATE RESEARCH DIRECTORY OUTREACH


Author: C.E. Pope ♦ Download Chapter ♦ Download Lecture Slides & Notes

"The same medycyne ys good for herte brenning."
Med Bk c 1450 AD

A. Objectives
  1. Understand the anatomy of the esophagus and how the anatomy relates to propulsion, surgical resection, and the natural history of esophageal carcinoma.
  2. Understand the initiation and action of swallowing which includes opening and closing of two sphincters, and primary and secondary peristalsis.
  3. Master the pathophysiology and the consequences of gastroesophageal reflux disease, and how this knowledge allows a plan of therapy.
  4. Be able to discuss an algorithm for dysphagia (difficulty with swallowing).
B. General Structure/Function of the Gut

GI tract begins at pharyngeal-esophageal junction The gastrointestinal tract proper is usually considered to begin at the pharyngeal-esophageal junction. Before considering the structure and function of the esophagus, it might be well to discuss the structure and function of the oral cavity.

The tongue and teeth manipulate and shred the ingested solid food and reduce the bolus to an assimilable size. Difficulties in the esophageal handling of food can often be exaggerated by poor dental equipment, which may allow too large pieces to be swallowed.

Initial Swallowing After the food is sufficiently prepared, the tongue presses the bolus back into the pharynx. This initiates swallowing, an automatic sequence during which different groups of pharyngeal muscles contract in beautifully timed rhythm. At the same moment, respiration is automatically halted, and the larynx is elevated against the epiglottis to seal off the vocal cords and trachea. Temporary failure of this sequence can lead to "food going down the wrong pipe." Permanent failure, as is seen in some neurologic conditions such as cerebrovascular accident (stroke), can be devastating; such failure can lead to malnutrition and pulmonary aspiration.

Essence of esophageal function: transport material to the stomach and keep it there. It is time to leave the bolus of food temporarily suspended in the pharyngeal region in order to consider the anatomy and function of the esophagus, whose only real function is to convey food and liquid to the stomach, and to keep it there. It usually does this in an unobtrusive and automatic fashion. Failure of this transport function can lead to annoying or occasionally life-threatening complications. The esophagus also functions as a passive conduit for the retrograde passage of gas and during vomiting.

The esophagus is the usual portal of entry to the gut, whose different portions (esophagus, stomach, small and large bowel and gall bladder) each have unique characteristics which allow them to perform the specialized functions of digestion. Yet there are certain similarities in structure and function shared by all of these organs. Smooth muscle is present in most of the gut wall and it is uniquely qualified to power transport of materials and to maintain tone and shape during storage functions of the gut.

Smooth muscle cells contain myosin and actin filaments whose arrangements are not as ordered as the fibers in skeletal striated muscle. The speed of contraction of smooth muscle is slower than that of striated muscle, but the ability to maintain a certain cell length without the use of large amounts of energy allows maintenance of tone in the body of the organ and closure of specialized sphincteric zones. There are specialized direct connections between the muscle cells which allow propagation of impulses to occur. Smooth muscle cells receive less direct innervation than does skeletal muscle. There are receptors for hormones and other substances directly on the muscle membranes allowing for regulation of myogenic contraction. Nerve impulses can also be transferred to the muscle cells and affect the contractile state of the muscle cell. Changes in free intracellular calcium serve as the final initiating step in contraction.

Muscle cells maintain a negative resting potential as a result of sodium being pumped out of the interior of the cell. Fluctuations in the resting membrane potential increase or decrease the excitability of the cell. In some portions of the gut, specialized cells, the interstitial cells of Cajal, may be responsible for generating cyclic variations in cell potential which time the frequency of rhythmic contractions (basic electrical rhythm).

The smooth muscle is organized into an inner circular region, contraction of which tends to narrow or obliterate the lumen. An outer longitudinal layer shortens the bowel when it contracts. Between the two layers of muscle lies the myenteric plexus (Auerbach’s plexus) containing the cell bodies of excitatory and inhibitory motor nerves and sensory nerves. Axons from these cell bodies project either orad (towards the mouth) or caudad (towards the anus). A less well-developed plexus (Meissner), containing mostly sensory nerve cell bodies, lies in the submucosa which separates the epithelial lining of the gut from the circular muscle. These two plexi with their interconnecting nerve filaments form the enteric nervous system which controls the motor, sensory and secretory function of the gut with modulatory input from the sympathetic and parasympathetic fibers from the central nervous system.

To complete the general organization of the gut, it is necessary to mention the serosa or adventitia which is the outermost encompassing layer of the gut. This layer consists mostly of fibrous tissue. Each of the specific portions of the gastrointestinal tract will have specific modifications of this general scheme which has been outlined. It is now time to return to the esophagus.

Next Section (C): Structure of the Esophagus »



© Copyright University of Washington Division of Gastroenterology 1999-2008