ESOPHAGUS & THYMUS

DR. AJELETI A. O.

OUTLINE

• ESOPHAGUS

• ESOPHAGEAL CONSTRICTIONS

• THYMUS

• CLINCAL CORRELATES

Learning objective

• By the end of this lecture, students should be able to:

• Know the anatomy of the esophagus and their anatomical relations.

• Know the esophageal constrictions and their anatomical relations.

• Know the detailed blood supply and innervation of the esophagus.

• Have the knowledge of the thymus and its clinical importance

• Have understanding of the esophagus clinical correlates.

ESOPHAGUS

• The oesophagus, which is 25cm long, extends from the level of the lower border of the cricoid cartilage at the level of the 6th cervical vertebra to the cardiac orifice of the stomach

• The upper 5% of the esophagus consists of skeletal muscle only. The middle 45% of the esophagus consists of both skeletal muscle and smooth muscle interwoven together. The distal 50% of the esophagus consists of smooth muscle only.

ESOPHAGUS

ESOPHAGUS

• The esophagus descends into the posterior mediastinum from the superior mediastinum, passing posterior to and to the right of the arch of the aorta, and and posterior to the pericardium and left atrium.

• The esophagus constitutes the primary posterior relationship of the base of the heart. It then deviates to the left and passes through the esophageal hiatus in the diaphragm at the level of the T10 vertebra, anterior to the aorta.

FIVE NORMAL ESOPHAGEAL CONSTRICTIONS

• The esophagus is compressed by three structures: -the arch of the aorta -the left main bronchus -the diaphragm. • SPHINCTERS Upper Esophageal Sphincter (UES) The UES is skeletal muscle that separates the pharynx from the esophagus. Lower Esophageal Sphincter (LES) The LES is smooth muscle that separates the esophagus from the stomach. It prevents gastroesophageal reflux.

RELATIONS • Anteriorly, it is crossed by the trachea, the left

bronchus,the pericardium (separating it from the left atrium) and the diaphragm.

• Posteriorly lie the thoracic vertebrae, the thoracic duct, the azygos vein and its tributaries and, near the diaphragm, the descending aorta.

RELATIONS

• LEFT SIDE it is related to the left subclavian artery, the terminal part of the aortic arch, the left recurrent laryngeal nerve, the thoracic duct and the left pleura.

• In the posterior mediastinum it relates to the descending thoracic aorta before this passes posteriorly to the oesophagus above the diaphragm.

• RIGHT SIDE there is the pleura and the azygos vein. Below the root of the lung the vagi form a plexus on the oesophagus, the left vagus lying anteriorly, the right posteriorly.

BLOOD SUPPLY- ARTERIAL SUPPLY

• Inferior thyroid arteries (subclavian artery → thyrocervical trunk →inferior thyroid artery) supply the cervical esophagus

• Four to five branches from the descending thoracic aorta supply the thoracic esophagus

• Left gastric artery (abdominal aorta →celiac trunk →left gastric artery) supply the abdominal esophagus.

VENOUS DRAINAGE

• Inferior thyroid veins (inferior thyroid veins → brachiocephalic veins →superior vena cava) drain the cervical esophagus

• Esophageal plexus of veins (esophageal plexus of veins →azygous veins →superior vena cava) drain the thoracic esophagus

• Left gastric vein (left gastric vein →portal vein →hepatic sinusoids →central veins →hepatic veins → inferior vena cava) drain the abdominal esophagus

INNERVATION

• Somatic nervous system- upper portion only

• Enteric nervous system, which in the esophagus consists of the myenteric plexus of Auerbach only. The enteric nervous system is modulated by the parasympathetic and sympathetic nervous systems.

SOMATIC INNERVATION

• Cervical level 1 (C1) that travel with the hypoglossal nerve (cranial nerve [CN] XII) to innervate the opening muscles of the UES (thyrohyoid and geniohyoid muscles).

PARASYMPATHETIC

• CN X preganglionic axons that enter the esophageal plexus.

• CN X postganglionic neuronal cell bodies located in the enteric nervous system & axons terminate on mucosal glands, submucosal glands, and smooth muscle

• Neuronal cell bodies located in the nucleus ambiguus send axons that run in CN X (recurrent laryngeal nerves) and enter the esophageal plexus. These axons terminate on the closing muscles of the UES (inferior pharyngeal constrictor and cricopharyngeus muscle) and the esophageal skeletal muscle.

SYMPATHETIC

• Preganglionic axons form the greater splanchnic nerve.

• Postganglionic neuronal cell bodies are located in diffuse ganglia along the esophagus and celiac ganglion.

• Postganglionic axons synapse in the complex circuitry of the enteric nervous system.

LYMPHATIC DRAINAGE

• The lymphatic drainage is from a peri-oesophageal lymph plexus into the posterior mediastinal nodes, which drain both into the supraclavicular nodes and into nodes around the left gastric vessels.

• It is not uncommon to be able to palpate hard, fixed supraclavicular nodes in patients with advanced oesophageal cancer.

THYMUS

THYMUS • Is a bilobed structure, lying in the neck anterior to the

trachea and the anterior part of the superior mediastinum. • Attains its greatest relative size in the neonate. • Playing a key role in the development of the immune

system in early life but continues to grow until puberty. • T-lymphocyte precursors migrate to the thymus, where

they develop into T lymphocytes. • It undergoes a gradual involution, in which the thymic

tissue is replaced by fat. T lymphocytes (thymocytes) migrate out of the thymus to the peripheral lymphoid organs - spleen, tonsils, and lymph nodes.

• There they further differentiate into mature immunologically competent cells, which are responsible for cell-mediated immune reactions.

THYMUS- RELATIONS

• It is usually most prominent in children, where it may extend from the level of the fourth costal cartilages to the lower poles of the thyroid gland.

• In front of it lie the sternohyoid and sternothyroid muscles, the manubrium and upper part of the body of the sternum and their adjacent costal cartilages.

• Behind it are the pericardium, the arch of the aorta with its three large branches, the left brachiocephalic vein and the trachea.

BLOOD SUPPLY & LYMPH DRAINAGE

• BLOOD SUPPLY

• Small branches from the inferior thyroid and internal thoracic arteries, and there are corresponding veins. enter the thymus

• Frequently a relatively large short thymic vein enters the left brachiocephalic vein

• LYMPH DRAINAGE

• Efferent channels drain into parasternal, tracheobronchial and brachiocephalic nodes.

• The thymus does not receive any afferent lymphatics.

CLINICAL CORRELATE

• Achalasia of esophagus is a condition of impaired esophageal contractions because of failure of relaxation of the inferior esophageal sphincter, resulting from degeneration of myenteric (Auerbach’s) plexus in the esophagus. It causes an obstruction to the passage of food in the terminal esophagus and exhibits symptoms of dysphagia for solids and liquids, weight loss, chest pain, nocturnal cough, and recurrent bronchitis or pneumonia.

• Systemic sclerosis (scleroderma) is a systemic collagen vascular disease and has clinical features of dysphagia for solids and liquids, severe heartburn, and esophageal stricture.

CLINICAL CORRELATE

• Enlarged left atrium

• Bronchogenic carcinoma

• Malignant tumors of the esophagus

• Sliding hiatal hernia

• Paraesophageal hiatal hernia

• Esophageal reflux

• Esophageal Strictures (Narrowing).

• Barrett Esophagus

Text & Image Sources: Acknowledgement

• Drake, Vagi & Mitchell. 2015. Gray’s Anatomy for Students 3rd Ed; Churchill Livingstone Elsevier Inc. Philadelphia

• Agur & Dalley II. 2013. Grant’s Atlas of Anatomy, 13th Ed; Lippincott Williams & Wilkins. Philadelphia.

• Sinnatamby C.S. 2011. Last’s Anatomy Regional & Applied Anatomy, 12th Ed; Churchill Livingstone Elsevier Inc. Philadelphia

• Moore, Dally II & Agur. 2014. Lippincott Williams & Wilkins. Philadelphia.

• Chung & Chung. 2012. BRS Gross Anatomy, 7th Ed; Lippincott Williams & Wilkins. Philadelphia.

• Harold Ellis; 2006. Clinical Aantomy 11th Ed; Black Publishing