Esophageal Motility

Introduction

Esophageal motility involves coordinated activity of striated and smooth muscles, both controlled by vagal innervation. Unlike other regions, it lacks slow waves. Swallowing initiates peristalsis, while lower esophageal sphincter relaxation is mediated by inhibitory neurotransmitters for effective bolus transit.

• The esophagus functions as a conduit, transporting food from the pharynx to the stomach.
• Entry of the bolus initiates reflex peristaltic contractions, which propel contents efficiently into the stomach.

Functional Anatomy

Parts of Esophagus

• The esophagus is divided into three parts: upper esophageal sphincter, body, and lower esophageal sphincter.
• The upper region contains striated muscle, the middle region has mixed muscle, and the lower region consists of smooth muscle.
• All muscle layers receive vagal innervation, including striated fibers.

Special Features

• The esophagus lacks slow waves, unlike other gastrointestinal segments, resulting in lower intrinsic excitability.
• The esophageal body remains relaxed at rest and contracts only during swallowing.
• Swallowing initiates primary peristalsis through neural reflex pathways.
• Local distension by residual bolus triggers secondary peristalsis. ·  These coordinated mechanisms ensure efficient transport of food from the pharynx to the stomach.

Esophageal Sphincters

Upper Esophageal Sphincter

• The esophageal sphincters regulate movement of food and prevent reflux.
• The upper esophageal sphincter functions mainly as a physiological sphincter. It relaxes reflexly during swallowing to permit entry of the bolus into the esophagus.
• After passage of food, it contracts to prevent regurgitation into the pharynx.

Lower Esophageal Sphincter

• The lower esophageal sphincter maintains a tonic contraction at rest. It relaxes during swallowing to allow food to enter the stomach.
• This sphincter prevents gastroesophageal reflux under normal conditions. Its basal tone is partly maintained by cholinergic vagal activity.
• Relaxation during peristalsis is mediated by inhibitory neurotransmitters such as nitric oxide and vasoactive intestinal peptide, ensuring coordinated bolus transfer.

Esophageal Peristalsis

Esophageal peristalsis occurs in two forms: primary and secondary.

Primary Peristalsis

• Primary peristalsis is initiated by the swallowing reflex.
• A contraction wave forms above the bolus and propels it toward the stomach. It occurs even with swallowing of saliva, without the presence of food.

Secondary Peristalsis

• Secondary peristalsis is triggered when the bolus is not cleared by primary waves. It is initiated by mechanoreceptors responding to esophageal distension.
• This reflex ensures complete clearance of residual contents from the esophagus.

Applied Physiology

Reflux Esophagitis and Barrett’s Esophagus

• The lower esophageal sphincter maintains tonic contraction to prevent reflux of gastric contents.
• Incompetence of this sphincter leads to reflux esophagitis, caused by exposure of esophageal mucosa to acid.
• Patients commonly experience retrosternal burning pain, often referred to as heartburn.
• Chronic acid exposure may result in ulceration, stricture, or metaplastic changes such as Barrett’s esophagus.
• Management includes proton pump inhibitors or histamine receptor blockers to reduce acid secretion.
• In severe cases, fundoplication surgery reinforces the sphincter and prevents reflux.

Barrett’s Esophagus

• Barrett’s esophagus is a condition where chronic acid reflux causes replacement of normal squamous epithelium with columnar epithelium.
• It is a premalignant condition with increased cancer risk.

Achalasia Cardia

• Achalasia cardia is a motility disorder in which the lower esophageal sphincter fails to relax during swallowing.
• This results in impaired esophageal emptying, leading to retention of food and progressive dilation of the esophagus.

Causes

• The underlying cause is degeneration of the myenteric plexus, which reduces inhibitory neurotransmitters such as nitric oxide and vasoactive intestinal peptide.
• As a result, the sphincter maintains an abnormally high resting tone.
• Patients commonly present with dysphagia, regurgitation, chest discomfort, and weight loss.

Diagnosis

• Diagnosis is supported by barium swallow imaging, which shows a dilated esophagus with a narrowed distal segment, often described as a tapering appearance.
• Endoscopic examination may reveal retained food and fluid within the esophagus.

Treatment

• Initial treatment includes pneumatic dilatation to reduce sphincter pressure.
• Pharmacological therapy may involve agents that decrease sphincter tone, including botulinum toxin injections.
• In advanced cases, surgical myotomy is performed to improve esophageal emptying.

Aerophagia

• Aerophagia refers to involuntary swallowing of air during eating or drinking.
• A portion of swallowed air is expelled by belching, while the rest passes into the intestine.
• Intestinal bacteria produce gases such as carbon dioxide, hydrogen, methane, and hydrogen sulphide. These gases are eliminated as flatus through the rectum.
• The gastrointestinal tract produces about one liter of gas daily, while approximately 200 milliliters is present at a given time.
• The odor of flatus is mainly due to sulphur-containing compounds.

• Excess aerophagia or altered gut flora may cause abdominal discomfort and audible intestinal sounds.