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Secondary pulmonary lobule

Radswiki and Dr Frank Gaillard et al.

The secondary pulmonary lobule is the functional unit of the lung and is the key to HRCT terminology.

Secondary pulmonary lobules measures between 1 and 2.5 cm across. They are polyhedral in shape bounded by fibrous septa (the interlobular septa) which are themselves continuous with the peribronchovascular interstitium (axial connective tissue) and pleura (peripheral connective tissue).

Each lobule contains a up to a dozen acini and 30 - 50 primary pulmonary lobules.

Each secondary pulmonary lobule is supplied by a terminal bronchiole and a pulmonary artery branch. They are drained by pulmonary veins which form in at the periphery of the lobule and pass though the interlobular septa.

There are two sets of lymphatics: the first runs with the arteries in the peribronchovascular insterstitium; the second in the interlobular septa and drains to the subpleural plexus.

Within the secondary lobule, separating adjacent acini is a much less pronounced network of supporting connective tissue which forms the intralobular septa.