Gross Anatomy of the Lungs

The lungs are cone-shaped organs enclosed within the ribcage in the thoracic cavity. Their apex lies beneath the clavicle, while the base sits on the diaphragm. Enveloped by the pleurae, the lungs connect to the mediastinum through vascular and bronchial links at the lung root, where the hilum serves as an entry and exit point for vessels, bronchi, and nerves.

The right lung is larger and wider than the left lung, with greater volume. The left lung features a cardiac notch, an indentation that accommodates the heart. Structurally, the right lung divides into three lobes via oblique and horizontal fissures, while the left lung has only two lobes separated by an oblique fissure.

Bronchopulmonary segments are functional units within each lung lobe, separated by connective tissue septa. Each segment receives its own tertiary bronchus and artery. The right lung contains ten segments, while the left lung has eight to ten. These segments further divide into smaller hexagonal structures called lobules, visible at the lung surface.

The pulmonary artery carries deoxygenated blood from the pulmonary trunk to the lungs, branching continuously to mirror bronchial structure. Near the alveoli, pulmonary arteries become capillary networks devoid of smooth muscle. These capillaries form the respiratory membrane when meeting alveolar walls, enabling oxygen absorption by erythrocytes and oxygenated blood drainage via pulmonary veins.

The parasympathetic and sympathetic nervous systems govern airway dilation and constriction. The parasympathetic system induces bronchoconstriction, while the sympathetic system induces bronchodilation. Sensory fibers from the vagus nerve and thoracic ganglia enter at the hilum, forming the pulmonary plexus and branching along bronchi to innervate muscle fibers, glands, and blood vessels.

The lungs have distinct surfaces that interface with surrounding structures. The costal surface contacts the ribs, while the mediastinal surface contacts the mediastinum. The apex represents the superior region beneath the clavicle, and the base is the lower region resting on the diaphragm, creating multiple contact points within the thoracic cavity.

Pulmonary lobules are subdivisions formed as bronchi branch into bronchioles, each receiving a single bronchiole with multiple branches. One arteriole and one venule service each lobule. Interlobular septa, connective tissue walls, separate adjacent lobules, creating distinct functional units that facilitate organized gas exchange and blood flow throughout the lung tissue.