Scanning electron micrograph (SEM) of the inner surface of the human bronchus (one of the 2 main forks of the trachea - windpipe, which supply the lungs), showing a cancerous tumour (the rounded mass on right of image). The left side of the image shows normal bronchial epithelium, pitted with the entrances to glands & composed of ciliated epithelial cells, mucous cells, & blood vessels: this region is capable of warming, humidifying & filtering inspired air. Cancers of the air passages & the lung are common in western countries & are strongly linked to cigarette smoking & exposure to air pollutants (including asbestos). Mag. X 28 (10x8 size).