What is the hilum of the lung?

The hilum of the lungs is a triangular-shaped anatomical area located on the mediastinal surface of each lung, close to the cardiac impression, just above the middle mediastinum. In this area, lung tissue meets the bronchi, veins, and other structures that form the lung root. The structures that anchor the lungs to the trachea and heart are also found in the hilum of the lung.

In general, in human anatomy, the hilum of an organ refers to a depression or fissure in that organ through which other structures such as blood vessels, nerves, lymphatic vessels, etc., enter and exit. It is very common for the organ root to be found at the hilum, and for this reason hilum and root are often used interchangeably in many contexts, for example, in the University of Michigan Atlas of Anatomy, hilum and lung root are used. to refer to the same area.

Location

The body has two lungs, one on each side of the chest cavity. The two lungs are separated from each other by the trachea and heart. The area in which the trachea and heart are located is known as the middle mediastinum, and the surface of the lungs facing the mediastinum is known as the face or mediastinal surface.

The hilum of the lung is located in the upper half of the mediastinal surface of each lung. The hilum of the right lung lies behind the superior vena cava and behind part of the right atrium and under the arch of the azygos vein. The hilum of the left lung is situated below the aortic arch, in front of the descending aorta. Anterior to each hilum is the phrenic nerve, pericardiophrenic vessels, and the pulmonary plexus. At the back is the vagus nerve.

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Structure and characteristics

The rib cage and lungs are separated by a membranous lining called the pleura which has two layers, the visceral pleura, closest to the lung tissue, and the parietal pleura. At the hilum of the lung, the two pleurae are connected, serving as a point of union between the mediastinum and the pleural cavity.

The hilum is formed by a reflex of the pleura that surrounds the corresponding bronchus, pulmonary vein, pulmonary artery, bronchial veins and arteries, pulmonary plexus nerves, lymphatic vessels, pulmonary lymph nodes, and loose connective tissue. From the hilum, the visceral pleura descends forming what is known as the pulmonary ligament or triangular ligament of the lung.

The left and right hilum are not symmetrical. In each one we find this order of structures (see attached graphs):

Right pulmonary hilum (top to bottom): eparterial bronchus, pulmonary artery, hypothermic bronchus, and pulmonary veins. Left pulmonary hilum (top to bottom): pulmonary artery, bronchi, and pulmonary veins.

Gallery

Diagram of parts of lung Mediastinal surface of left lung Mediastinal surface of right lung

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