The lungs are large, air filled, vital organs. Both the right and left lungs are encased by membranes called the pleurae which are contained within and protected by the thoracic cage, also known as the rib cage. The wide inferior border of the lungs is in contact with the diaphragm and is called the base. The narrow, pointed superior portion of the lungs is called the apex.

The region between the right and left lungs is the mediastinum. This is where the heart, thymus, and great blood vessels are located. The main bronchi penetrate each lung on the medial surface in a region called the hilum. Blood vessels, nerves, and lymphatic vessels also enter the lung in the hilum, and then branch extensively throughout the lung. Each lung is divided into anatomically distinct lobes by fissures, with each lobe containing a portion of the bronchial tree leading into the alveoli.

The right and left lung also have unique characteristics:

Right lung

  • Slightly shorter and wider than the left lung

  • 3 lobes: superior, middle, and inferior

  • 2 fissures:

    • Horizontal fissure separates the superior and middle lobes

    • Oblique fissure separates the middle and inferior lobes

Left lung

  • Slightly longer and narrower than the right lung

  • 2 lobes: superior and inferior

  • Superior lobe has the cardiac notch, an indentation on the medial surface occupied by the heart

  • 1 fissure:

    • Oblique fissure separates the superior and inferior lobes

Figure 1: The lobular structure of the lungs.