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The trachea, oesophagus, and thoracic duct are the principal midline structures within the superior and posterior mediastina of the thoracic cavity.
They form the vital airway, food passage, and lymphatic drainage channels connecting the head and neck with the thoracoabdominal region.
The trachea (windpipe) is a fibrocartilaginous tube forming the lower part of the respiratory passage.
Extends from the lower border of the cricoid cartilage (C6) to the level of the sternal angle (T4/T5), where it divides into the right and left principal bronchi (tracheal bifurcation).
Length: 10–12 cm
Diameter: 2 cm in adults
Cervical Part:
Lies in the neck, in front of the oesophagus, extending from C6 to the thoracic inlet.
Thoracic Part:
Lies within the superior mediastinum, descending to the level of T4/T5, where it bifurcates at the carina.
Anteriorly:
Skin, fascia, isthmus of thyroid gland (2nd–4th tracheal rings)
Inferior thyroid veins
Arch of aorta (below)
Brachiocephalic trunk and left brachiocephalic vein
Thymus (in children)
Posteriorly:
Oesophagus
On Each Side:
Right side: Azygos vein, right vagus nerve, pleura, and SVC.
Left side: Arch of aorta, left common carotid and subclavian arteries, and left recurrent laryngeal nerve.
Composed of 16–20 C-shaped hyaline cartilaginous rings.
The open posterior part is closed by the trachealis muscle (smooth muscle), allowing flexibility and diameter adjustment.
The rings prevent collapse during inspiration.
Arterial:
Inferior thyroid artery (cervical part)
Bronchial arteries (thoracic part)
Venous Drainage:
Inferior thyroid veins and bronchial veins.
Pretracheal and paratracheal lymph nodes, draining ultimately to deep cervical nodes.
Sensory and secretomotor: Vagus nerve.
Sympathetic fibers: From middle cervical ganglion (for vasomotor control).
Mucosa:
Lined by pseudostratified ciliated columnar epithelium with goblet cells (respiratory epithelium).
Contains basal cells (stem cells), brush cells, and small granule cells.
Cilia move mucus upward toward the pharynx (mucociliary escalator).
Lamina Propria:
Loose connective tissue with seromucous glands, lymphoid tissue, and blood vessels.
Submucosa:
Rich in seromucous glands producing mucus for lubrication.
Cartilaginous Layer:
Contains hyaline cartilage rings, providing structural rigidity.
Adventitia:
Connective tissue binding trachea to adjacent structures.
Tracheostomy:
Surgical opening made between 2nd and 4th tracheal rings to establish an airway.
The isthmus of the thyroid gland is often divided or retracted during the procedure.
Foreign Body in Trachea:
Objects tend to enter the right bronchus (wider, shorter, and more vertical).
May cause coughing, choking, and respiratory distress.
Tracheitis and Bronchitis:
Inflammation of the tracheal mucosa, often viral or bacterial.
Leads to productive cough and irritation due to involvement of mucous glands.
Tracheal Stenosis:
Narrowing due to prolonged intubation, trauma, or congenital defect.
Compression Syndromes:
Aortic aneurysm, enlarged thyroid (goitre), or mediastinal tumors can compress the trachea → dyspnea or stridor.
Carina:
The ridge at the tracheal bifurcation (most sensitive area of trachea).
Stimulates cough reflex when irritated; displaced in lung collapse or tumor.
Tracheoesophageal Fistula:
Congenital or acquired abnormal communication between trachea and oesophagus, leading to choking during feeding.
Tracheomalacia:
Weakness of tracheal cartilages leading to collapse during respiration, especially in infants.
Bronchoscopy:
Diagnostic procedure to visualize the tracheobronchial tree, remove foreign bodies, or take biopsy samples.
Intubation:
Endotracheal tube insertion to maintain airway during anesthesia or respiratory failure.
The trachea’s structural balance between rigidity (cartilage) and flexibility (trachealis muscle) allows uninterrupted airflow, while its mucociliary system ensures a clean, protected airway — a design elegant in both function and simplicity.
The oesophagus is a muscular tube about 25 cm long that connects the pharynx (C6) to the stomach (T11).
It passes through the neck, thorax, and diaphragm, entering the abdomen through the oesophageal opening at T10 level.
Parts:
Cervical part – from C6 to thoracic inlet
Thoracic part – from thoracic inlet to diaphragm
Abdominal part – from diaphragm to cardiac end of stomach (about 1.25 cm long)
In the neck:
Lies behind trachea and in front of vertebral column.
Laterally related to recurrent laryngeal nerves and carotid sheath.
In the thorax:
Initially lies behind trachea and then behind left atrium.
Shows three normal constrictions:
At cricoid cartilage (C6)
Where it is crossed by aortic arch (T4)
Where it passes through diaphragm (T10)
Anterior relations: Trachea (above), left atrium (below)
Posterior relations: Vertebral column, thoracic duct, aorta (below)
To the left: Aortic arch, left subclavian artery, thoracic duct, left pleura and lung
To the right: Azygos vein, right pleura and lung
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Cervical part: Inferior thyroid arteries
Thoracic part: Oesophageal branches of aorta
Abdominal part: Oesophageal branches of left gastric artery
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Upper part → Brachiocephalic veins
Middle part → Azygos vein
Lower part → Left gastric vein (portal system)
→ Site of porto-systemic anastomosis, significant in portal hypertension
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Cervical → Deep cervical nodes
Thoracic → Posterior mediastinal nodes
Abdominal → Left gastric nodes
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Parasympathetic:
Upper half – Recurrent laryngeal nerves
Lower half – Oesophageal plexus (from vagus) → forms anterior & posterior gastric nerves
→ Function: Motor, sensory, and secretomotor
Sympathetic:
From middle cervical ganglion (upper part) and upper thoracic ganglia (lower part)
→ Function: Vasomotor
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The oesophagus is specialized for rapid propulsion of food.
Mucosa:
Epithelium: Stratified squamous non-keratinized — protective.
Lamina propria: Rich in connective tissue with papillae and lymphoid elements.
Muscularis mucosae: Indistinct in upper part, distinct in lower part.
Submucosa:
Contains mucus-secreting glands (oesophageal glands proper).
Muscularis externa:
Upper third: Striated muscle
Middle third: Mixed (striated + smooth)
Lower third: Smooth muscle
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Adventitia:
Loose connective tissue with blood vessels and nerves
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Oesophageal Varices:
Dilatation of lower oesophageal veins in portal hypertension due to portal-systemic anastomosis.
May rupture → haematemesis (vomiting of blood)
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Tracheo-Oesophageal Fistula:
Congenital failure of separation between trachea and oesophagus → choking during feeding
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Achalasia Cardia:
Failure of lower oesophageal sphincter to relax → dysphagia and regurgitation, due to absence of ganglion cells
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Oesophageal Compression:
Mediastinal tumors or aortic aneurysm cause dysphagia (difficulty swallowing)
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Barium Swallow Study:
Demonstrates three normal constrictions and detects strictures, carcinoma, or varices.
Left atrial enlargement produces indentation on anterior wall of oesophagus
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Endoscopy:
Used for biopsy, stricture dilation, or foreign body removal; knowledge of constrictions essential to avoid perforation
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The thoracic duct is the largest lymphatic vessel in the human body.
It extends from the upper abdomen to the lower part of the neck, traversing the posterior and superior mediastina.
Length: approximately 45 cm (18 inches).
It shows a beaded appearance due to numerous valves in its lumen
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Origin: Continuation of the cisterna chyli, located near the lower border of T12 vertebra.
Entry into Thorax: Through the aortic opening of the diaphragm.
Posterior Mediastinum: Ascends from T12 to T5, lying between the aorta (left) and azygos vein (right), anterior to the vertebral column.
At T5, it crosses from the right to the left side, ascending along the left edge of the oesophagus.
Superior Mediastinum: Continues upward on the left side of the oesophagus.
In the Neck:
Arches laterally at the level of C7 transverse process.
Curves downward in front of the first part of the left subclavian artery.
Termination: Opens into the left venous angle, i.e., the junction between the left subclavian and left internal jugular veins
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.At the Aortic Opening of the Diaphragm
Anteriorly: Diaphragm
Posteriorly: Vertebral column
Right side: Azygos vein
Left side: Aorta
In Posterior Mediastinum
Anteriorly: Diaphragm, oesophagus, right pleural recess
Posteriorly: Vertebral column, right posterior intercostal arteries, terminal parts of hemiazygos veins
Right side: Azygos vein
Left side: Descending thoracic aorta
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In Superior Mediastinum
Anteriorly: Arch of aorta, origin of left subclavian artery
Posteriorly: Vertebral column
Right side: Oesophagus
Left side: Pleura
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In the Neck
Anteriorly: Left common carotid artery, left vagus nerve, left internal jugular vein
Posteriorly: Vertebral artery and vein, sympathetic trunk, thyrocervical trunk, left phrenic nerve, medial border of scalenus anterior, prevertebral fascia, and first part of left subclavian artery
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.The thoracic duct drains lymph from:
Both sides below the diaphragm, and
Left side above the diaphragm (i.e., left side of head, neck, thorax, and left upper limb).
Specific Tributaries:
Posterior mediastinal lymph vessels
Intercostal lymph vessels
Left jugular trunk – drains left side of head and neck
Left subclavian trunk – drains left upper limb
Left bronchomediastinal trunk – drains left thoracic viscera
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.Chylothorax:
Leakage of lymph (chyle) into the pleural cavity due to injury or rupture of the thoracic duct during surgery or trauma.
Manifests as milky pleural effusion rich in fat.
Obstruction of Thoracic Duct:
May result from malignancy (e.g., lymphoma), tuberculosis, or fibrosis, causing lymphedema of the left arm, left face, and lower body.
Congenital Absence or Duplication:
Rare anomalies affecting drainage pattern, sometimes leading to bilateral chylothorax.
Surgical Relevance:
Thoracic duct must be preserved during neck dissections, oesophageal surgeries, or mediastinal procedures to prevent postoperative chyle leak.
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