Oesophagus
The oesophagus is a muscular tube that connects the throat (pharynx) to the stomach. It plays a key role in the digestive system by transporting food, liquids, and saliva after swallowing.
How It Works
When you swallow, the food or liquid enters the oesophagus. The walls of the esophagus are lined with muscles that contract in a wave-like motion. This movement is called peristalsis, and it helps push the food down toward the stomach.
At the lower end of the oesophagus is a ring-like muscle called the lower oesophageal sphincter (LES). This muscle opens to let food into the stomach and then closes to prevent stomach contents—especially acid—from flowing back up. If this muscle doesn't close properly, it can lead to acid reflux or heartburn.
Structure and Location
The oesophagus is about 20–25 cm (8–10 inches) long in adults.
It runs from the back of your throat, behind the trachea (windpipe), through the chest, and ends at the top of the stomach.
It passes through a small opening in the diaphragm (the muscle that helps with breathing) before connecting to the stomach.
Inner circular layer: These fibers encircle the esophagus and are responsible for peristalsis, the wave-like contractions that propel food downwards.
Outer longitudinal layer: These fibers run along the length of the esophagus and are thought to assist with peristalsis.
The composition of these muscle layers varies along the esophagus's length:
Upper third: Primarily striated (skeletal) muscle, under the control of the central nervous system.
Lower third: Primarily smooth muscle, regulated by both the central nervous system and intrinsic mechanisms within the esophageal wall.
Middle third: A transitional zone containing a mixture of both striated and smooth muscle.
Additionally, the esophagus contains two specialized ring-shaped muscles called sphincters at its ends:
Upper Esophageal Sphincter (UES): Located at the junction of the pharynx and esophagus, it's primarily composed of skeletal muscle and relaxes during swallowing to allow food to enter.
Lower Esophageal Sphincter (LES): Located at the junction of the esophagus and stomach, it's composed of smooth muscle and remains contracted most of the time to prevent acid reflux.
Nerves Controlling LES Opening and Closing
The opening and closing of the LES are intricately controlled by the nervous system, mainly through vagal pathways originating in the brainstem.
Relaxation (opening) of the LES: This is primarily mediated by inhibitory neurons that release nitric oxide (NO). These neurons are stimulated by the vagus nerve in response to swallowing.
Contraction (closing) of the LES: This is mainly maintained by the myogenic tone of the smooth muscle and is also influenced by excitatory cholinergic nerves (releasing acetylcholine).
Creation of Wave-Like Movements (Peristalsis)
Peristalsis, the wave-like muscle contractions that propel food through the esophagus, is a coordinated process involving both nerve activity and muscle contractions.
Initiation: Swallowing triggers the primary peristaltic wave, originating from the brainstem's swallowing center.
Mechanism: As the food bolus enters the esophagus, nerves stimulate a wave of relaxation ahead of the bolus, followed by a wave of contraction behind it. The circular muscles contract, squeezing the food, while the longitudinal muscles shorten the segment of the esophagus, pushing the food forward.
Secondary Peristalsis: If the initial wave isn't sufficient to move the entire bolus, the esophageal lining's stretch receptors trigger secondary peristaltic waves until the food enters the stomach.
Opening of the Esophagus
The opening of the esophagus at its upper end is surrounded by the Upper Esophageal Sphincter (UES), formed by the cricopharyngeus muscle.
Parts of the Esophagus
The esophagus is commonly divided into three main anatomical segments:
Cervical Esophagus: The uppermost section, located in the neck, extending from the pharynx to the suprasternal notch.
Thoracic Esophagus: The longest portion, located in the chest within the mediastinum, extending from the suprasternal notch to the diaphragm.
Abdominal Esophagus: The shortest section, located in the abdominal cavity after passing through the diaphragm, and connecting to the stomach.
5
Cervical Esophagus: This is the uppermost part of the esophagus and is located in the neck, behind the trachea. It begins at the lower border of the cricoid cartilage (level of C6 vertebra), which is the narrowest part of the esophagus, and extends down to the suprasternal notch, according to the National Cancer Institute (NCI).
Thoracic Esophagus: This is the longest section and runs through the chest cavity (thorax), lying within the mediastinum, an area between the lungs. It extends from the suprasternal notch to the diaphragm. This segment passes behind the trachea, the aortic arch, and the left main bronchus.
Abdominal Esophagus: This is the shortest part, located in the abdominal cavity. It begins where the esophagus passes through the esophageal hiatus, an opening in the diaphragm, and terminates at the cardia of the stomach, where it connects to the stomach.
These anatomical divisions help describe the esophagus's location and relationships with surrounding structures.