Expansion
Upper third striated, middle third mixed, lower third smooth
Expansion
- Upper third - striated (voluntary) muscle
- Middle third - mixed
- Lower third - smooth (involuntary) muscle
Both layers, inner circular and outer longitudinal, follow this transition.
The clinical value lies in localising dysphagia. Stroke, motor neurone disease and myasthenia gravis affect the striated upper oesophagus and pharynx, producing difficulty initiating a swallow, coughing and nasal regurgitation. Achalasia, systemic sclerosis and diffuse oesophageal spasm affect the smooth lower oesophagus, producing food sticking retrosternally.
Note also that the oesophagus has no serosa over most of its length, only adventitia. This is one reason oesophageal tumours spread early and anastomoses heal poorly.