Читать книгу The Esophagus - Группа авторов - Страница 111

The esophagus is a hollow muscular tube with sphincters at either end. The upper esophageal sphincter (UES) is formed by the fibers of the cricopharyngeus, a skeletal muscle that is contiguous with pharyngeal muscles proximally, and the striated muscle in the proximal esophagus distally. The transition between skeletal muscle in the proximal esophagus and smooth muscle in the distal esophagus occurs in the proximal third of the tubular esophagus. The lower esophageal sphincter (LES) is formed entirely of smooth muscle. The main functions of the esophagus are to transport ingested content from the pharynx into the stomach, and to clear noxious gastric content refluxed into the esophagus. Esophageal motor function includes esophageal primary and secondary peristalsis, esophageal shortening, and esophageal tone. These functions are dependent on control mechanisms, both peripheral and central, interrelated with oral and pharyngeal function, airway function, gastric function, as well as relationships to other intrathoracic organs, both central and peripheral. Both motor and sensory pathways exist between the esophagus and the central nervous system, which interface with ganglia and postganglionic nerves located in between circular and longitudinal muscle layers of the esophagus.

The esophagus is unique in its anatomy and physiology. The swallowing process combines volitional central control mechanisms with involuntary/reflex controls, both central and peripheral. The esophagus transits through cavities of different pressures, from atmospheric pressure at the mouth, to negative intrathoracic pressure, to positive intra‐abdominal pressure, with sphincters separating pressures and organ contents in each cavity. The sphincters open temporarily to allow the passage of food aborally and air and gastric contents orally with belching and vomiting.

Understanding of central and peripheral control mechanisms for swallowing, and particularly esophageal function, derives from animal experimentation. Since species can differ in physiologic mechanisms, application of animal findings to human physiology may not be perfect and needs to be kept in mind. Studies of central mechanisms are derived from animals with a totally striated muscle esophageal body (such as the sheep, rat, mouse, ferret, and dog). The LES is composed of smooth muscle in all species. Studies in species with a significant portion of the esophageal body composed of smooth muscle, such as the opossum, cat, and to a lesser extent the non‐human primate and humans, have provided a large amount of information about the peripheral control mechanisms in the smooth muscle esophageal body and LES.