The lingula of the lung is a tongue-shaped region of the left lung. It is also known by its Latin name, lingula pulmonis sinistri, which means little tongue of the left lung. The lingula represents an analog for the middle lobe of the right lung, which is absent in the left lung due to the position of the heart on the left side of the thoracic cavity.
The lingula is located on the anterior side of the left lung, inferior to the cardiac notch and superior to the oblique fissure. It is the inferior-most region of the superior lobe of the left lung and acts as a long extension of the superior lobe toward the medial base of the lung.
The lingula is divided into two segments: the superior lingula and the inferior lingula. Each segment receives its air supply from its own tertiary bronchus — the superior lingular bronchus and inferior lingular bronchus, respectively — and works as a discrete unit within the lung.
Air inhaled into the body enters the left lung through the left primary bronchus, which bifurcates into the superior and inferior lobar bronchi. Each secondary bronchus provides air to one lobe of the lung. The superior lobar bronchus further divides into four tertiary bronchi to provide air to each of the bronchopulmonary segments of the lobe. Two of the tertiary bronchi, the superior lingular bronchus and the inferior lingular bronchus, carry air to the lingula. Upon reaching the lingula, each tertiary bronchus further divides into many bronchioles to deliver air to all of the tissues of the lung. At the end of the bronchioles are many tiny cup-like hollows known as alveoli, which receive the air and serve as the functional units of the lungs. Blood passes through capillaries surrounding the thin epithelial walls of the alveoli, allowing exchange of gases between the blood and air. The net result of the interface between air and blood is the absorption of oxygen from the air into the blood and the release of carbon dioxide from the blood into the air. Air is then expelled through exhalation out of the body and replaced by fresh air during the next inhalation.