Phrenic Nerve, Trachea and Esophagus

Question 1

[8-minute video]: course of vagus nerve from the carotid sheath upto posterior mediastinum.

Answer 1

😎

Question 2

State the root values of phrenic nerve and state the structures it innervates.

Answer 2

C3, C4, C5
Motor innervation: thoracic diaphragm
Sensory innervation: fibrous pericardium, mediastinal pleura, and diaphragmatic peritoneum

Question 3

State the course of the phrenic nerve in the neck upto thorax.

Answer 3

anterior scalene (anterior surface) ⇒ over the dome of the pleura ⇒ posterior to the subclavian vein ⇒ thorax

Question 4

In the thorax, the right and left phrenic nerves have different courses, but both maintain contact with the mediastinal pleura and travel anterior to bronchus on their respective side.
State the course of the right phrenic nerve in the thorax.

Answer 4

right side of the right brachiocephalic vein and superior vena cava ⇒ anterior to root of right lung ⇒ right side of pericardium ⇒ right side of the inferior vena cava ⇒ diaphragm ⇒ caval opening of diaphragm ⇒ central peritoneum

Question 5

In the thorax, the right and left phrenic nerves have different courses, but both maintain contact with the mediastinal pleura and travel anterior to bronchus on their respective side.
State the course of the left phrenic nerve in the thorax.

Answer 5

left side of left subclavian artery ⇒ left side of aortic arch ⇒ crosses left side of the left vagus nerve ⇒ anterior to root of left lung ⇒ over left pericardium ⇒ diaphragm ⇒ caval opening of diaphragm ⇒ central peritoneum

Question 6

State the extents of the trachea.

Answer 6

From lower border of cricoid cartilage/lower border of C6 vertebra to lower border of T4 vertebra in the thorax where it bifurcates into right and left principal bronchi [at the level of the sternal angle].

Notes:
㊨ The extent of trachea varies as follows:
~ C6 to T4 in cadaver placed in supine position.
~ C6 to T6 in living individuals in standing position.
~ C6 to T3 in newborn.
㊨ The lumen of the trachea is kept patent by 16–20 C-shaped rings of hyaline cartilage.
㊨ The gap between the posterior free ends of C-shaped cartilages is bridged by a band of smooth muscle (trachealis) and a fibroelastic ligament, which permit expansion of esophagus during the passage of bolus of food.
㊨ The arrangement of cartilages and elastic tissue in the tracheal wall prevents its kinking and obstruction during the movements of the head and neck.

Question 7

State the arterial blood supply, venous drainage and lymphatic drainage to the trachea.

Answer 7

Arterial supply: inferior thyroid artery, branches of bronchial artery
Venous drainage: into left brachiocephalic vein
Lymphatic drainage: pretracheal and paratracheal lymph nodes

Question 8

State the nerve supply to the trachea.

Answer 8

Nerve supply occurs by the autonomic nerve fibres:
☛ Parasympathetic fibres are sensory and secretomotor to the mucous membrane, and motor to the trachealis muscle.
☛ Sympathetic fibres are vasomotor.

Question 9

The carina is a keel-like median ridge in the lumen at the bifurcation of trachea. State its importance.

Answer 9

㊨ Functional importance: The mucosa of trachea over the carina is most sensitive. The cough reflex is usually initiated here, which helps to clear the sputum.
㊨ Pathological significance: It is visible as a sharp sagittal ridge at the tracheal bifurcation during bronchoscopy, hence serves as a useful landmark. It is located about 25 cm from the incisor teeth and 30 cm from the nostrils. If the tracheobronchial lymph nodes in the angle between the main (principal) bronchi are enlarged due to spread of bronchiogenic carcinoma, the carina becomes distorted and flattened.

Question 10

State the extents of the esophagus.

Answer 10

From the lower border of C6 vertebra to the cardiac orifice of the stomach at level of T11 vertebra.

Question 11

Describe the curvatures that the esophagus presents.

Answer 11

1. Two side-to-side curvatures, both towards the left.
   a) First at the root of the neck, before entering the thoracic inlet.
   (b) Second at the level of T7 vertebra, before passing in front of the descending thoracic aorta.
2. Two anteroposterior curvatures.
   (a) First corresponding to the curvature of cervical spine.
   (b) Second corresponding to the curvature of thoracic spine.

Question 12

Describe the constrictions of the esophagus.

Answer 12

Normally, there are four sites of anatomical constrictions/ narrowings in the esophagus. The distance of each constriction is measured from the upper incisor teeth.
1. First constriction, at the pharyngo-esophageal junction, 9 cm (6 inches) from the incisor teeth.
2. Second constriction, where it is crossed by the arch of aorta, 22.5 cm (9 inches) from the incisor teeth.
3. Third constriction, where it is crossed by the left principal bronchus, 27.5 cm (11 inches) from the incisor teeth.
4. Fourth constriction, where it pierces the diaphragm, 40 cm (15 inches) from the incisor teeth.

Note: The narrowest part of esophagus is its commencement at the cricopharyngeal sphincter.

Question 13

State the significance of esophageal constrictions.

Answer 13

The anatomical constrictions of esophagus are of considerable clinical importance due to the following reasons:
1. These are the sites where swallowed foreign bodies may stuck in the esophagus.
2. These are the sites where strictures develop after ingestion of caustic substances.
3. These sites have predilection for the carcinoma of the esophagus.
4. These are sites through which it may be difficult to pass esophagoscope/gastric tube.

Question 14

The esophagus is divided into three parts; cervical part, thoracic part, abdominal part. State the extents of each part.

Answer 14

Cervical part: from lower border of cricoid cartilage to superior border of manubrium sterni
Thoracic part: from superior border of manubrium sterni to the esophageal opening in the diaphragm.