Pulmonary Lymph Nodes

The pulmonary lymph nodes, also known as intrapulmonary lymph nodes, are small lymphatic structures located within the lung parenchyma. They are primarily associated with the segmental and subsegmental bronchi and play a crucial role in the first stage of lymphatic drainage from the lungs. These nodes filter lymph from peripheral lung tissues before it is relayed to the bronchopulmonary (hilar) nodes.

Location

• Located within the lung substance along the course of the segmental bronchi
• Most concentrated near the lobar and segmental bronchi
• Present in both the right and left lungs

Afferent Drainage

These nodes receive lymph from:

• Peripheral alveolar and bronchiolar regions
• Terminal bronchioles and respiratory bronchioles
• Visceral pleura via subpleural lymphatic plexuses

Efferent Drainage

• Lymph flows from the pulmonary nodes into the bronchopulmonary (hilar) lymph nodes
• From there, lymph continues through the tracheobronchial nodes and into the paratracheal nodes

Function

• First filtration point for lymph from alveoli and deep lung tissues
• Traps inhaled pathogens, carbon particles, and tumor cells
• Activates immune responses within the pulmonary lymphatic system

Relations

• Medial: Segmental bronchi
• Lateral: Lung alveoli and pleura
• Superior: Lobar bronchi and pulmonary artery branches
• Inferior: Continuation toward bronchopulmonary nodes

Histological Features

• Cortex: Contains lymphoid follicles with germinal centers
• Medulla: Contains cords of lymphocytes and macrophages
• Subcapsular sinus: Site of lymph entry from afferent vessels
• Enclosed in a thin connective tissue capsule

Clinical Significance

• Black pigmentation: Commonly seen in smokers and urban dwellers due to carbon-laden macrophages
• Enlargement: Can occur in infections (pneumonia, tuberculosis) or early pulmonary carcinoma
• Not easily visible: Typically not seen on imaging unless enlarged or calcified

Topographic Summary

• Location: Within lung tissue, near segmental bronchi
• Afferents: From alveoli, bronchioles, and pleura
• Efferents: To bronchopulmonary (hilar) lymph nodes
• Function: Initial filtration of lymph from lung parenchyma