Trachea and Esophagus

Trachea

The trachea, or windpipe, is a flexible fibrocartilaginous tube that conducts air from the larynx to the principal bronchi. Its lumen is maintained by 16–20 C-shaped rings of hyaline cartilage.

Location

The trachea lies in the lower part of the neck and extends into the superior mediastinum.

Extent

• It begins as a continuation of the larynx at the lower border of the cricoid cartilage, opposite the lower border of the C6 vertebra.
• It ends by dividing into the right and left principal bronchi.
• The level of tracheal bifurcation varies with respiration, posture, and age. It is generally related to the plane of the sternal angle and may descend to lower thoracic levels during inspiration.

Dimensions

• Length: Approximately 10–11 cm
• External diameter: About 2 cm in males and 1.5 cm in females
• Internal diameter:
  • Smaller in the living individual than in the cadaver
  • About 3 mm at one year of age
  • During childhood, the diameter in millimetres roughly corresponds to age in years
  • About 12 mm in adults

Relations of Thoracic Part of Trachea

Anterior

1. Manubrium sterni
2. Left brachiocephalic vein
3. Brachiocephalic trunk
4. Left common carotid artery
5. Arch of the aorta
6. Deep cardiac plexus
7. Thymus or its remnants

Posterior

1. Esophagus
2. Left recurrent laryngeal nerve
3. Vertebral column

On the right

1. Right lung and pleura
2. Right vagus nerve
3. Azygos vein

On the left

1. Arch of the aorta
2. Left common carotid artery
3. Left subclavian artery
4. Left lung and pleura

Structure

The wall of the trachea consists of four principal layers:

1. Mucosa
2. Submucosa
3. Cartilaginous and muscular layer
4. Adventitia

The mucosa is lined by pseudostratified ciliated columnar epithelium containing:

• Ciliated columnar cells
• Goblet cells that secrete mucus
• Brush cells with sensory functions
• Small granule or neuroendocrine cells
• Basal cells that act as progenitor cells

The epithelium rests on a prominent basement membrane. Beneath it, the lamina propria contains connective tissue and lymphoid elements associated with the respiratory mucosa.

The tracheal wall contains 16–20 C-shaped rings of hyaline cartilage. The open posterior ends of these rings are bridged by fibroelastic tissue and the trachealis muscle, which consists of smooth muscle.

Externally, the trachea is surrounded by a fibroelastic adventitia that anchors it to adjacent structures.

Vascular Supply, Lymphatic Drainage, and Nerve Supply

• Arterial supply: Mainly from the inferior thyroid arteries
• Venous drainage: Through veins that ultimately drain into the brachiocephalic venous system
• Lymphatic drainage: Mainly to pretracheal, paratracheal, and tracheobronchial lymph nodes
• Nerve supply: Autonomic fibers from parasympathetic and sympathetic sources.
  1. Parasympathetic supply: Parasympathetic fibers reach the trachea through the vagus and recurrent laryngeal nerves. They provide sensory innervation to the mucosa, stimulate glandular secretion, and influence trachealis muscle tone.
  2. Sympathetic supply: Sympathetic fibers arise from the cervical sympathetic trunk and reach the trachea along blood vessels. They primarily provide vasomotor innervation.

Esophagus

The esophagus is a muscular tube lined by mucosa that connects the pharynx with the stomach. It is divided into three parts:

1. Cervical part
2. Thoracic part
3. Abdominal part

Measurements

• Length: Approximately 25 cm
• Width: About 2 cm
• The lumen is normally collapsed and opens during the passage of food.

Course

The esophagus begins as a continuation of the pharynx at the lower border of the cricoid cartilage, opposite the C6 vertebra.

It descends anterior to the vertebral column through the superior and posterior mediastina.

The esophagus passes through the esophageal hiatus of the diaphragm at T10 and enters the stomach at the cardiac orifice, approximately at the level of T11.

Curvatures

The esophagus shows both anteroposterior and lateral curvatures.

Anteroposterior curvatures

• The upper curvature follows the curvature of the cervical vertebral column.
• The lower curvature corresponds to the curvature of the thoracic vertebral column.

Lateral curvatures

The esophagus deviates toward the left at two levels:

1. Near the root of the neck
2. Around the level of T7

Constrictions

The esophagus has four clinically important constrictions:

1. Pharyngoesophageal constriction: Located at the junction of the pharynx and esophagus, approximately 15 cm from the upper incisor teeth. It is produced mainly by the cricopharyngeus part of the inferior pharyngeal constrictor.
2. Aortic constriction: Produced where the esophagus is crossed by the arch of the aorta, approximately 23 cm from the upper incisors.
3. Bronchial constriction: Occurs where the esophagus is crossed by the left main bronchus, approximately 28 cm from the upper incisors.
4. Diaphragmatic constriction: Located where the esophagus passes through the diaphragm, approximately 40 cm from the upper incisors.

These constrictions are clinically important because foreign bodies may lodge at these sites, and strictures are commonly assessed in relation to them during endoscopy.

Table 17.1: Sites of esophageal constrictions

Constriction	Location	Distance from upper incisor teeth	Vertebral level
First	Pharyngoesophageal junction	15 cm (6 inches)	C6
Second	Crossing of the arch of the aorta	23 cm (9 inches)	T4
Third	Crossing of the left main bronchus	28 cm (11 inches)	T6
Fourth	Passage through the diaphragm	40 cm (15 inches)	T10

Relations of Esophagus

Approximate lengths of the three parts are:

1. Cervical part: 4–5 cm
2. Thoracic part: 18–20 cm
3. Abdominal part: 1–2 cm

Relations of thoracic part of esophagus

Anterior

• Trachea
• Arch of the aorta
• Right pulmonary artery
• Left main bronchus
• Pericardium and left atrium
• Diaphragm

Posterior

• Vertebral column
• Right posterior intercostal arteries
• Azygos vein
• Terminal portions of the hemiazygos and accessory hemiazygos veins
• Thoracic duct
• Descending thoracic aorta

To the right

• Right lung and pleura
• Azygos vein
• Right vagus nerve

To the left

In the superior mediastinum:

• Arch of the aorta
• Left subclavian artery
• Left recurrent laryngeal nerve
• Thoracic duct
• Left lung and pleura

In the posterior mediastinum:

• Descending thoracic aorta
• Left lung and pleura

Blood Supply, Lymphatic Drainage, and Nerve Supply

Arterial supply

1. Cervical part: Inferior thyroid artery
2. Thoracic part: Esophageal branches of the thoracic aorta, with contributions from bronchial arteries
3. Abdominal part: Left gastric and inferior phrenic arteries

Venous drainage

1. Cervical part: Drains mainly into the inferior thyroid veins.
2. Thoracic part: Drains into the azygos and hemiazygos venous systems.
3. Abdominal part: Drains predominantly into the left gastric vein, which belongs to the portal venous system. It also communicates with systemic esophageal veins draining into the azygos system.

The lower end of the esophagus is therefore an important site of portosystemic venous anastomosis.

Lymphatic drainage

1. Cervical part: Deep cervical lymph nodes
2. Thoracic part: Posterior mediastinal and tracheobronchial lymph nodes
3. Abdominal part: Left gastric and celiac lymph nodes

Nerve supply

The esophagus receives autonomic innervation from sympathetic and parasympathetic fibers.

• Sympathetic fibers: Arise mainly from thoracic sympathetic pathways. They carry vasomotor fibers and visceral afferent fibers associated with pain.
• Parasympathetic fibers: Derived mainly from the vagus nerves. In the upper esophagus, fibers also reach it through the recurrent laryngeal nerves.
• Parasympathetic fibers influence esophageal motility and glandular secretion.

Histology

The wall of the esophagus consists of four main layers:

1. Mucosa: Lined by nonkeratinized stratified squamous epithelium. Beneath the epithelium are the lamina propria and muscularis mucosae, which contains predominantly longitudinal smooth muscle fibers.
2. Submucosa: Composed of dense connective tissue containing elastic fibers, blood vessels, nerves, and mucous esophageal glands.
3. Muscularis externa:
   • Upper one-third: predominantly skeletal muscle
   • Middle one-third: mixture of skeletal and smooth muscle
   • Lower one-third: smooth muscle
4. Adventitia: Most of the esophagus is surrounded externally by connective tissue forming an adventitia. The short abdominal segment is partly covered by serosa.

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