The Human Aerodigestive Tract and Gastroesophageal Reflux: An Evolutionary Perspective

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Abstract

In order to appreciate fully the nature of supraesophageal complications of gastroesophageal reflux in humans, it is essential to view the problem within an evolutionary framework. Examination of the aerodigestive tract anatomy of our mammalian relatives shows that this region in humans is highly derived as compared to other mammals. Among the specializations that adult humans exhibit is a caudal position of the larynx, which results in a permanently expanded oropharynx. These anatomical features underlie our distinctive breathing and swallowing patterns and provide the substrate that allows for the production of articulate speech. While the selection factors that have shaped human evolution obviously favored our derived aerodigestive tract, aspects of this anatomy appear particularly unsuited to accommodate gastroesophageal reflux. Indeed, our unique aerodigestive tract morphology may predispose us to an array of supraesophageal complications of gastroesophageal reflux.

Section snippets

Comparative Anatomy of the Mammalian Aerodigestive Tract: The Basic Pattern

Before exploring those specializations of the human aerodigestive tract that may be of particular interest to the clinician, it is important to outline the general “plan,” or condition, of this region in mammals. The class Mammalia is, of course, a large and varied group, including terrestrial and aquatic species who exhibit a range of dietary behaviors (e.g., herbivorous, omnivorous, carnivorous). Although no typical mammal can be said to exist, the general “plan” for their aerodigestive

Human Patterns: From the Basic Plan to a Unique Configuration

The aerodigestive tract of adult humans is the end product of both our evolutionary history as well as a unique ontogenetic process. Although all mammals undergo maturation of aerodigestive tract functions,[17]few species appear to undergo as radical a developmental rearrangement of structures in the region as do humans. Indeed, the dramatic changes that occur in the human aerodigestive tract, and the highly specialized end product, are hallmarks of Homo sapiens.

One of the most striking

The Human Aerodigestive Tract and GERD: A Template for Trouble

It is only by placing the adult human aerodigestive tract in the above developmental and comparative contexts that an appreciation can be gleaned of how our derived structural specializations affect both normal and abnormal upper respiratory and upper digestive behaviors. If we are to understand fully the human supraesophageal response to retrograde flow of gastroesophageal contents, we must first see how certain other mammals respond to retrograde incursions into their supraesophagus and, in

Acknowledgements

We wish to express our appreciation to Dr. Reza Shaker both for his invitation to Dr. Laitman to participate in the Symposium on Supra-esophageal Complications of Reflux Disease, and for creating the stimulating and productive environment at the symposium. Components of our research have been funded by Office of Naval Research (ONR) grant N00014-96-1-0764 and NSF Grants 9634519 and 9528100.

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