Anatomy of the Diaphragm

Study Notes

The thoracic cavity contains the mediastinum, pleurae, lungs, trachea, and diaphragm.

The aortic opening transmits the aorta, thoracic duct, and azygos vein.
The esophageal opening lies at the level of the 10th thoracic vertebra and transmits the esophagus, right and left vagus nerves.
The caval opening lies at the level of the 8th thoracic vertebra in the central tendon and transmits the inferior vena cava and terminal branches of the right phrenic nerve.

The mediastinum is a movable partition that extends superiorly to the thoracic outlet and the root of the neck and inferiorly to the diaphragm.
It contains the remains of the thymus, the heart and large blood vessels, the trachea and esophagus, the thoracic duct and lymph nodes, the vagus and phrenic nerves, and the sympathetic trunks.

The pleurae have two parts: a parietal layer and a visceral layer.
The parietal layer lines the thoracic wall and is divided into cervical, costal, diaphragmatic, and mediastinal pleura.
The visceral layer completely covers the outer surfaces of the lungs and extends into the depths of the interlobar fissures.
The two layers become continuous with one another by means of a cuff of pleura that surrounds the structures entering and leaving the lung at the hilum of each lung.

The trachea is a mobile cartilaginous and membranous tube.
It is about 11.25 cm long and 2.5 cm in diameter.
Blood supply: upper two-thirds from the inferior thyroid arteries, lower third from the bronchial arteries.
Nerve supply: sensory nerve supply from the vagi and the recurrent laryngeal nerves, sympathetic nerves supply the trachealis muscle.

The trachea bifurcates behind the arch of the aorta into the right and left principal (main) bronchi.
The right principal bronchus is wider, shorter, and more vertical than the left and is about 2.5 cm long.
The left principal bronchus is narrower, longer, and more horizontal than the right and is about 5 cm long.
The bronchi divide dichotomously, giving rise to several million terminal bronchioles that terminate in one or more respiratory bronchioles.

The diaphragm is a thin muscular and tendinous septum that separates the chest cavity above from the abdominal cavity below.
It is pierced by the structures that pass between the chest and the abdomen.
The diaphragm is the most important muscle of respiration.
It is dome-shaped and consists of a peripheral muscular part and a centrally placed tendon.
The origin of the diaphragm can be divided into three parts: sternal, costal, and vertebral parts.
The diaphragm curves up into right and left domes, with the right dome reaching as high as the upper border of the 5th rib and the left dome reaching the lower border of the 5th rib.
On contraction, the diaphragm pulls down its central tendon and increases the vertical diameter of the thorax.
The diaphragm has three main openings: aortic, esophageal, and caval openings.