MEDICAL PHYSIOLOGY

Detailed explanation-1: -The esophagus is subdivided into three anatomical segments: cervical, thoracic, and abdominal.

Detailed explanation-2: -The third constriction is approximately 40 cm from the upper incisor, where it pierces the diaphragm and forms the physiologic lower esophageal sphincter at the tenth thoracic vertebra.

Detailed explanation-3: -The upper third of the esophagus contains striated muscle, the lower third contains smooth muscle, and the middle third contains a mixture of both. Muscle is arranged in two layers: one in which the muscle fibers run longitudinal to the esophagus, and the other in which the fibers encircle the esophagus.