B FIGURE 22.2. Bronchioles and alveoli. The small bronchiole(B)seen here is lined by a cuboidal epithe lium and smooth muscle. The large adjacent arteriole(A) is a branch of the pulmonary artery. The veins or venules (V) run in septa. The alveolar walls(arrow)are normally lined with flat type I epithelium. of which only the nuclei are visible. Alveolar macrophages(arrowheads) are common.7