Lobule of lung

The parenchyma of the lung is composed of secondary lobules which, although closely connected together by an interlobular areolar tissue, are quite distinct from one another, and may be teased asunder without much difficulty in the fetus. The secondary lobules vary in size; those on the surface are large, of pyramidal form, the base turned toward the surface; those in the interior smaller, and of various forms. Each secondary lobule is composed of several primary lobules, the anatomical units of the lung. The primary lobule consists of an alveolar duct, the air spaces connected with it and their bloodvessels, lymphatics and nerves.