Lungs

The lungs are paired respiratory organs located in the right and left hemithorax, responsible for gas exchange between air and blood. Each lung is covered by pleura, housed in the pleural cavity, and attached to the mediastinum only by its hilus, through which the main bronchi, pulmonary arteries and veins, nerves, and lymphatic vessels pass. Each lung has:

• A convex costal surface in contact with the ribs,

• A flat mediastinal surface bearing the cardiac impression,

• Ventral and dorsal borders, delimiting the costal and mediastinal surfaces.

The lobation of the lungs varies between species.

Right lung:

• Dogs, cats, ruminants: divided into four lobes:

  • Cranial lobe: the most anterior, apex near the thoracic inlet.

  • Middle lobe: ventral, contributing to the V-shaped cardiac notch.

  • Caudal lobe: the largest, resting on the diaphragm.

  • Accessory lobe: medial, dorsal to the caudal vena cava.

• Horse: only three lobes (cranial, caudal, accessory), middle lobe absent.

• Human: three lobes (upper, middle, lower).

Left lung:

• Dogs, cats, ruminants: divided into two lobes:

  • Cranial lobe, subdivided into cranial and caudal parts.

  • Caudal lobe, larger, resting on the diaphragm.

• Horse: similar, two main lobes, no middle or accessory lobe.

• Human: two lobes (upper and lower), separated by the oblique fissure.