Normal Lung

Small pieces of tissue can be taken from the lung, embedded in paraffin, cut thin, placed on a glass slide, and stained. The resulting preparations are examined with a microscope to make diagnoses of lung diseases. The two pictures below were taken from a normal lung.

Normal Lung on Microscopy

This is a low-magnification view of part of a lobule. It has small airways (bronchioles (B)) with adjacent branches of the pulmonary artery (A). The blood flows from the arteries into fine capillaries in the alveolar walls (the diffuse network) where gas exchange occurs. The blood then flows into the pulmonary veins (V) that carry the oxygenated blood back to the heart.

Note: When you are asked to find structures (see red type below), move the mouse over the picture and click on the appropriate structure. The pointer changes to a hand when it is over a labeled area. When you click, the answer will appear. Click on "Return" to come back to the picture.

Normal Small Airway

At higher magnification, we see a small airway (bronchiole), a structure that is often damaged by cigarette smoke. It is lined by a single layer of cells (epithelium) that have cilia on the surface (see below). Also, the airway wall has multiple alveolar walls attached to it. These walls are elastic and serve to keep the airway open during expiration, as the amount of air in the lungs decreases.

Find the airway (bronchiole). Click on the structure to see if you are right.

Find the alveolar walls with tiny vessels where gas exchange occurs. Only some are marked.

airwayalvwallNormal epithelium: Higher magnification of the epithelium lining a large airway shows the delicate, fuzzy cilia at the top of each cell. Cilia normally beat in the direction of the mouth. They are responsible for keeping the airways free of fine dust and germs. Tobacco smoke paralyzes the cilia and prevents this normal housekeeping function. Tobacco smoke also damages the cells and causes a continuing repair process to occur.

Find cilia.

Find epithelial cells lining the airway.

In the wall find glands that secrete mucus.

In the wall find cartilage (dark purple) that suppports the wall.



Think of the cilia as brooms that keep the lung clean. Don't let cigarette smoke prevent the broom from working.





























Bronchiole (small airway) lined with respiratory epithelium




























Alveolar walls that surround the alveoli (white spaces that contain air)



























Epithelial cells lining the airway

























































Cartilage. This stiff material supports the walls of the large airways to prevent them from closing during expiration. Cartilage is absent from the small airways (bronchioles).



























Glands. These secrete mucus to protect the surface epithelium.