The lungs are a pair of essential respiratory system organs located in the thorax. They provide gas exchange between the inhaled air and blood.

The lungs are somewhat conical-shaped, each with a rounded point at its apex and a flat base that rests on the convex surface of the diaphragm.

Located in the thoracic cavity, the lungs extend anteriorly and laterally from the heart to the rib cage and posteriorly to the thoracic spine.

The apex is a rounded upper tip of the superior end of each lung. It is situated above the superior thoracic aperture (thoracic inlet), more precisely, 1-2 centimeters above the clavicle, in the root of the neck, where it contacts the cervical pleura. The apex of each lung is covered by the suprapleural membrane.
The base of each lung is broad, semilunar, and concave. It lies upon the superior surface of the diaphragm. The concavity is deeper on the base of the right lung. Because of the liver, the diaphragm lies higher on the right side than on the left. That is also why the right lung is wider and shorter, while the left lung is longer and narrower.

Each lung has not only the apex and base, but it also contains three surfaces and three borders.

Surfaces of each lung are:

Costal surface - smooth, curved, and it contacts with the costal pleura; it is located against the internal surfaces of the ribs;
Medial (mediastinal) surface - a surface that is in contact with the mediastinum and structures that are located in it; the medial surface is divided into posterior vertebral and anterior mediastinal parts; the vertebral part is in contact with the sides of the thoracic spine, while the anterior mediastinal part is deeply concave because it has a cardiac impression, which is more prominent on the left lung where the heart projects;
Diaphragmatic surface - is concave and contacts the diaphragm.

Each lung presents the following borders:

Inferior border - separates the base with the diaphragmatic surface from the costal and mediastinal surfaces;
Anterior border - a thin and sharp margin that corresponds to the anterior (costomediastinal) line of the pleural reflection on the right side, while on the left side it corresponds to the same line only above the fourth costal cartilage; the cardiac notch lies on the anterior border of the left lung above the lingula, and it is a deep notch created by the apex of the heart; anterior border separates the costal and mediastinal surfaces;
Posterior border - a thick margin, divides the costal surface from the mediastinal surface of each lung.

Each lung also has a hilum located on the mediastinal surface, where the root of the lung enters, transmitting various structures. The main bronchi enter the lungs via the lung roots and branch into even smaller bronchi and bronchioles, forming the bronchial tree.

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Lungs