Pulmonary Ligament: Pleurae, Hilum of the Lungs, The Root of the Lung, and What is the Pulmonary Ligament?

pulmonary ligament anatomy

The Pulmonary Ligament is the supporting pleural fold that extends from the lower part of the lung from the hilum.

People can divide each lung into four main sections: apex, base, root, and hilum of the lung.

The hilum serves as the point of attachment between the lung root and the lung.

To understand what does this have to do with the Pulmonary Ligament some people need to learn about the structures around it.


The lungs remain separated from the rib cage thanks to two-layered membranous coatings called “pleurae.”

The Pleurae consist of serous membranes supported by connective tissue. Each pleura is made up of two layers: the parietal layer and the visceral layer.

The Parietal Layer covers the inner surface of the thoracic cavity. It is thicker than the Visceral Layer, and experts sometimes divide it according to the part of the body that gets in contact with this pleura.

Going by that perspective, people can subdivide the Parietal Pleura into the following:

  • The Mediastinal Pleura, which covers the lateral boundary of the mediastinum. It extends neck and lines the surface under the supra pleural membrane.
  • The Cervical Pleura, which lines the extension of the pleural cavity (the thin fluid-filled space between the two pulmonary pleurae) into the neck.
  • The Costal Pleura, which covers the inner part of the ribs, the costal cartilages, and the intercostal muscles.
  • The Diaphragmatic Pleura, which covers the thoracic surface of the diaphragm.

On the other hand, the Visceral Layer is the delicate serous membrane that covers the outer surface of the lungs and extends into the fissures between the lobes (the interlobar fissures).

Hilum of the Lung

The hilum is a large triangular depressed area, or a fissure, on the lung located on the medial aspect of each lung.

Medical experts tend to divide the Hilum of the Lung into “Left Hilum,” and “Right Hilum.”

The Left Hilum of the Lung is large, dense and pulled laterally and upwards to the left. In this particular area, the left pulmonary artery takes up most of the upper part.

Right below this area is the left main bronchus. Right there people can find two pulmonary veins, one in the front, and the other one below the left main bronchus.

In the Right Hilum of the Lung, people can find the bronchus at the dorsal boundary and the pulmonary artery at the ventral edge.

In this particular area, the upper lobe bronchus and pulmonary artery are just above the level of the right main bronchus and right pulmonary artery.

Just like in the case of the  Left Hilum, it’s a relatively simple task finding pulmonary veins in front and below the right main bronchus.

The Root of the Lung

It refers to a short, broad pedicle joining the middle outer layer of the lung with all the mediastinum, located at the hilum of each lung.

Experts consider that structures entering and leaving the lung at the hilum, such as the bronchus, pulmonary arteries/veins, the bronchial arteries/veins, nerves, as well as other vessels, nodes, and tissue, form the Root.

In fact, such structures connect the Root to the heart and the trachea.

A short sheet of parietal pleura covers the Root of the Lung at its front, above, and behind.

But at the lower border of the Root investing layers come into contact. They later extend into a mesenteric fold known as Pulmonary Ligament.

What is the Pulmonary Ligament?

The Pulmonary Ligament, also known as Inferior Pulmonary Ligament, is a fused triangular-shaped supporting pleural fold that extends from the hilum.

In Latin, the term used for Pulmonary Ligament is Ligamentum Pulmonale.

The Pulmonary Ligament sags down from the hilum of the lung, and it stretches between the pericardium and the lower part of the mediastinal area of the lung.

In other terms, it extends from the mediastinum (a space in the thorax that contains a group of non-delineated organs) to the medial surface of the lower lobe.

Its primary function is allowing vascular enlargement of the hilar vessels (interlobar artery, upper lobe arteries, left descending artery) in times of increased cardiac output.

At the apex of the Pulmonary Ligament, people can find the inferior pulmonary vein. Other contents of this particular area include the intrapulmonary lymph nodes and bronchial veins.