Examine slide 98, in which the lung section is stained to demonstrate elastic fibers in the lamina propria of bronchioles and in the tunica media of the larger arteries (Fig. 17-9b).

• In the visceral pleura note the abundant elastic fibers mixed with collagen fibers.
• Finally note the dark elastic fibers in the walls of alveoli.

What is the function of the visceral pleura?

Would you say lung tissue consists mostly of stroma or parenchyma?

On slide 97 or 98 use the low power objective to locate a region showing the terminal portion of a respiratory tree cut longitudinally as shown in Figs. 17-11 and 17-12. Identify the terminal bronchiole, respiratory bronchiole, alveolar duct, alveolar sac, and alveoli.

What differences in the epithelium distinguish the first 3 components just listed?

At what point do the capillaries in the airway wall become most important?

Clinical note: Emphysema, which is almost always due to the toxic effects of cigarette smoking, produces alveolar loss and enlargement of the air spaces beyond the terminal bronchioles due to chronic inflammation and the gradual destruction of pneumocytes and interalveolar septa. This reduces the total respiratory surface available for gas exchange, producing inefficient respiration. The affected tissue does not regenerate and the treatment includes the permanent use of oxygen-enriched air.

Pneumocytes and macrophages.