Examine this section of lung tissue that has been stained to demonstrate elastic fibers in the lamina propria.

• Elastic fibers are particularly evident in the walls of bronchioles and in the tunica media of arteries as seen in the image at the right.
• In the visceral pleura look for elastic fibers mixed with collagen fibers. Finally, look for the dark elastic fibers in the walls of alveoli.
   

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, elastic fibers, 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.