Читать книгу The Esophagus - Группа авторов - Страница 17

The esophagus has two types of muscle. The proximal one‐third of the esophagus is composed of skeletal muscle, the middle one‐third is composed of both smooth and skeletal muscle, and the distal one‐third is only smooth muscle. The muscle is arranged in two layers. The outer layer of muscle fibers runs longitudinal to the esophagus, while the second inner layer encircles the esophagus. Effective esophageal body peristalsis results from the coordinated contractile waves from both layers. Longitudinal muscle contraction moves ahead of circular muscle contraction and leads to esophageal shortening and localized luminal distension at the level of the food bolus. Circular muscle contraction then propels the food bolus down the esophagus and into the stomach [3].

The two muscular rings, the UES and the LES, bookend the top and bottom of the esophagus, respectively. The UES is made of skeletal muscle, is not under voluntary control, and opens following the initiation of a swallow. The LES, or cardiac sphincter, opens to allow passage of food from the esophagus into the stomach and, while closed, helps to prevent the reflux of gastric acidic contents. Dysfunction at the level of the LES due to low basal pressure can cause gastroesophageal reflux, which in turn can produce symptoms of heartburn and regurgitation, and if frequent enough, damage to the underlying esophageal mucosa [4]. Alternatively, elevated LES pressures are seen in motility disorders such as achalasia and often produce symptoms of dysphagia.