Muscular layer of esophagus

The muscular layer of esophagus (a.k.a. the muscularis externa), is responsible for the propulsion of food from the pharynx to the stomach by coordinated peristaltic contractions.

Functions of the inner circular and outer longitudinal layers

The muscularis externa of esophagus consists of an inner circular layer and an outer longitudinal layer of muscle. Contraction of the circular layer narrows the lumen, while contraction of the longitudinal layer shortens the oesophagus, together facilitating the movement of the food bolus towards the stomach.

Between these two muscle layers lies the myenteric (Auerbach's) plexus, an autonomic nerve plexus that coordinates oesophageal motility and peristalsis.

Transition from skeletal to smooth musculature

A distinctive feature of the muscularis layer of esophagus is the gradual transition from skeletal muscle to smooth muscle along its length.

• The upper one-third is composed predominantly of skeletal (striated) muscle, reflecting its involvement in the voluntary phase of swallowing.

• The middle one-third contains a mixture of skeletal and smooth muscle,

• The lower one-third consists entirely of smooth muscle under autonomic control.

This arrangement allows swallowing to transition from voluntary initiation to involuntary peristaltic propulsion.

Clinical correlates

The muscular layer of esophagus is important in several oesophageal disorders.

• Degeneration of the myenteric plexus may result in achalasia, characterised by impaired relaxation of the lower esophageal sphincter and progressive dysphagia.

• Conversely, dysfunction of the lower oesophageal sphincter can lead to gastro-esophageal reflux disease (GERD), in which gastric contents reflux into the oesophagus, causing inflammation and mucosal injury.