Human Anatomy Vol 1

THORAX

DISSECTION

Remove the posterior sudace of the parietal pericardium

between the right and left pulmonary veins. This

uncovers the anterior surface of the oesophagus in the

posterior mediastinum.

Find the azygos vein and its tributaries on the

vefiebral column to the right of the oesophagus. Find

and follow the thoracic duct on the left of azygos vein.

ldentify the sternal, sternocostal, interchondral and

costochondraljoints on the anterior aspect of chest wall

which was reflected downwards.

Expose the ligaments which unite the heads of the

ribs to the vertebral bodies and intervefiebral discs.

Feofules

The oesophagus is a narrow muscular tube, forming
the food passage between the pharynx and stomach. It
extends from the lower part of the neck to the uPPer
part of the abdomen (Fi9.20.4). The oesophagus is
about 25 cm long. The tube is flattened antero-
posteriorly and the lumen is kept collapsed; it dilates
only during the passage of the food bolus. The
pharyngo-oesophageal junction is the narrowest part
of the alimentary canal except for the vermiform
appendix.
The oesophagus begins in the neck at the lower
border of the cricoid cartilage where it is continuous
with the lower end of the pharynx.
It descends in front of the vertebral column through
the superior and posterior parts of the mediastinum,

and pierces the diaphragm at the level of tenth thoracic

vertebra. It ends by opening into the stomach at its

cardiac end at the level of eleventh thoracic vertebra.

Curvolures

In general, the oesophagus is vertical, but shows slight

curvatures in the following directions. There are two

side to side curvatures, both towards the Left (see

Fig. V.\. One is at the root of the neck and the other

near the lower end. It also has anteroposterior

curvatures that correspond to the curvatures of the

cervicothoracic spine.

Constriclions

Normally the oesophagus shows^4 constrictions at the

following levels.

1 At its beginning,^15 crr./5 inch from the incisor teeth,

where it is crossed by cricopharyngeus muscle.

2 \Mhere it is crossed by the aortic arch, 22.5 cm/9-inch

from the incisor teeth.

3 Where it is crossed by the left bronchus,^27 .5 cm / 17-

inch from the incisor teeth.

4 \A/here it pierces the diaphra gm37 .5 cml 15-inch from

the incisor teeth.

The distance from the incisor teeth are important in

passing instruments like endoscope into the

oesophagus.

For sake of convenience the relations of the

oesophagus may be studied in three parts-cervical,

thoracic and abdominal. The relations of the cervical

part are described in Volume 3, and those of the

abdominal part in Volume 2 of this book.

Relolions of lhe Thorocic Porl of the Oesophogus

A"nt*riorly

1 Trachea.

2 Right pulmonary artery.

3 Left bronchus.

4 Pericardium with left atrium.

5 The diaphragm (Figs20.2 and 20.3).

Fesferuorly

1 Vertebral column.

2 Right posterior intercostal artefies.

3 Thoracic duct.

4 Azygos vein with the terminal parts of the hemi-

azygos veins.

5 Thoracic aorta.

5 Right pleural recess.

7 Diaphragm (Fig. 20.4).

Fo fhe t

1 Right lung and pleura.

2 Azygos vein.

3 The right vagus (Figs 20.5a to c).

in cases of blockage of air pathway in nose or

larynx.

As the tracheal rings are incomplete posteriorly

the oesophagus can dilate during swallowing. This

also allows the diameter of the trachea to be

controlled by the trachealis muscle. This muscle

narrows the caliber of the tube, compressing the

contained air if the vocal cords are closed. This

increases the explosive force of the blast of com-

pressed air, as occurs in coughing and sneezing.

Mucus secretions help in trapping inhaled foreign

particles, and the soiled mucus is then expelled

by coughing. The cilia of the mucous membrane

beat upwards, pushing the mucus towards the

pharynx.

The trachea may get compressed by pathological

enlargements of the thyroid, the thymus, lymph

nodes and the aortic arch. This causes dyspnoea,

irritative cough, and often a husky voice.