Clinical meaning
Achalasia is a primary esophageal motility disorder characterized by the failure of the lower esophageal sphincter (LES) to relax during swallowing and the absence of normal peristalsis in the esophageal body. The condition results from progressive degeneration and loss of inhibitory ganglion cells within the myenteric (Auerbach) plexus of the esophageal wall. These ganglion cells normally release nitric oxide and vasoactive intestinal peptide (VIP), which are the primary neurotransmitters responsible for LES relaxation. When these neurons are destroyed, the LES remains in a state of sustained contraction, creating a functional obstruction at the gastroesophageal junction. The esophagus is a muscular tube approximately 25 centimeters long that connects the pharynx to the stomach. It consists of an outer longitudinal muscle layer and an inner circular muscle layer. The upper third contains striated muscle under voluntary control, the middle third contains a mixture of striated and smooth muscle, and the lower third is entirely smooth muscle. The LES is a 3-4 centimeter zone of tonically contracted smooth muscle at the distal esophagus that normally maintains a resting pressure of 15-25 mmHg to...