Pulmonary Lymph Nodes - Location, Function, Anatomy

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