Esophagus: Embryology & Gross Anatomy

• The esophagus.
• Presented by Dr. Khatim Alamin.

Embryology

• Development commences in the 3rd week of gestation.
• It is derived from the endoderm-lined yolk sac cavity/primitive gut.
• The tracheobronchial tree begins as a ventral diverticulum during the 3rd week.
• The mucosa is fully differentiated by week 12.
• The muscular layer starts forming from the mesoderm in the 6th week and is fully formed by week 12.
• By the 14th week, the initial functional swallow occurs and is well-established by the 4th month of gestation.

Gross Anatomy

• The esophagus is a muscular tube 25 cm long.
• It extends from the lower border of the cricoid cartilage to the stomach.
• The esophagus spans from the C6 to T11 vertebrae.
• The esophagus exhibits two curves in the coronal plane.
• There are three constrictions along its length.

Parts

• The esophagus is usually studied in three parts: cervical, thoracic and abdominal.
• Anatomical features, pathologies, surgical approach and management options are specific to each part.

Relations - Cervical Part

• Anteriorly, the cervical esophagus is related to the trachea.
• Posteriorly, it is related to prevertebral muscles and fascia covering the 6th to 8th cervical vertebrae.
• Laterally, relationships include the carotid sheath and lower poles of the thyroid gland.
• The thoracic duct is positioned on the left side at the C6 level.

Relations - Abdominal Part

• The abdominal part is a very short segment of variable length.
• Anteriorly, it features the esophageal groove on the posterior surface of the liver.
• It is related to the greater sac anteriorly and on the left side.
• The lesser sac peritoneum is located on the right side.
• The abdominal esophagus is closely related to the vagus nerves.

Gastroesophageal Junction

• Externally, the gastroesophageal junction features the Collar of Helvetius and the gastroesophageal fat pad.
• Endoscopically, the junction is marked by the Z line.
• It is where the smooth esophageal lining transitions to the rugal folds of the stomach.

Blood Supply

• The cervical part of the esophagus is supplied by the inferior thyroid artery.
• The thoracic part receives blood from bronchial and esophageal branches of the descending aorta.
• The abdominal part is supplied by ascending branches of the left phrenic and left gastric arteries.

Venous Drainage

• The venous drainage begins with a submucosal plexus, which drains into the periesophageal venous plexus, and then to the esophageal veins.
• The cervical esophagus drains into the inferior thyroid vein.
• The thoracic esophagus drains into the azygos vein, hemiazygos veins, intercostal veins, and bronchial veins.
• The abdominal esophagus drains into the left gastric vein
• The venous drainage creates a porto-systemic anastomosis.

Nerve Supply

• It consists of the enteric nervous system and the extrinsic nervous system components.
• The enteric nervous system includes Auerbach's plexus in the intermuscular plane and Meissner's plexus in the submucosal plane.
• The extrinsic nervous system includes parasympathetic supply from the vagus nerve via recurrent laryngeal nerves.
• Sympathetic supply comes from the thoracic spinal cord segments.

Lymphatic Drainage

• Lymphatic drainage from the lymphatic plexuses in the submucosa and muscularis to regional lymph nodes.
• The cervical esophagus drains into paratracheal, deep cervical and internal jugular nodes.
• The thoracic esophagus drains into mediastinal, paratracheal, subcarinal, retro cardiac, and infracardiac lymph nodes, and the thoracic duct.

Histology

• The esophagus consists of 4 layers: mucosa, submucosa, muscularis propria, and adventitial layer.
• The mucosa is composed of stratified squamous epithelium.
• The submucosa contains brenner's glands.
• The muscularis propria is composed of inner circular and outer longitudinal muscle fibers.
• The outermost layer is the adventitial layer.
• The esophagus lacks a serosal layer.

Overview of the esophagus, including its embryological development starting in the 3rd week of gestation from the endoderm-lined yolk sac, and its gross anatomy as a 25 cm muscular tube extending from the cricoid cartilage to the stomach. Key anatomical features and parts are discussed.