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# The Esophagus The esophagus is a muscular tube approximately 20-25 cm long, connecting the pharynx to the stomach. It is divided into three parts: * **Cervical:** Located behind the larynx; its skeletal muscle is innervated by the vagus nerve. * **Thoracic:** Located behind the larynx, trachea,...

# The Esophagus The esophagus is a muscular tube approximately 20-25 cm long, connecting the pharynx to the stomach. It is divided into three parts: * **Cervical:** Located behind the larynx; its skeletal muscle is innervated by the vagus nerve. * **Thoracic:** Located behind the larynx, trachea, heart, and aorta; its smooth muscle is innervated by the autonomic nervous system. * **Abdominal:** Located below the diaphragm, adjacent to the liver and stomach; its smooth muscle is innervated by the autonomic nervous system. # Deglutition (Swallowing) Deglutition (swallowing) is the process of moving food from the pharynx to the stomach. It takes several seconds and is a reflex action centered in the medulla oblongata. The process occurs in three distinct phases: 1. **Oral Phase:** This is a voluntary stage where food is prepared for swallowing and then transferred to the pharynx. 2. **Pharyngeal Phase:** This is an involuntary stage. The soft palate moves upward; the epiglottis (a flap of tissue) covers the trachea and the vocal cords close, preventing food from entering the trachea. The upper esophageal sphincter relaxes allowing food to enter the esophagus. Breathing stops momentarily due to a reflex action. Contractions of the pharyngeal muscles propel the food into the esophagus. 3. **Esophageal Phase:** This is also an involuntary stage. The upper esophageal sphincter relaxes (normally closed except during swallowing) and the esophageal muscles contract in peristaltic waves, causing the food to move to the stomach. The first few centimeters of the esophagus are composed of striated muscle, and contraction causes the food to move into the smooth muscle portion of the esophagus.