Biology Department Courses


The alveoli of the lung are where gas exchange occurs.  They are made of simple squamous epithelia, which allows for rapid and efficient gas exchange between the air space and the capillaries that lie within the alveolar walls.  The alveolar walls are indicated by the arrowheads.  Although it is difficult to see the walls of the capillaries, the bright pink crescent shaped cells are red blood cells (arrows), present within the capillaries of the alveolar walls.  There is an arteriole in the upper right of the image.