Alveoli in the lungs, fish gills and the villi in the small intestine are adapted so that they have short diffusion distance, big concentration difference and large surface area. This means that ...

These three features are particularly important to our lungs for efficient ... such as the small intestine, body tissues and placenta. Thin lining: the lining of the alveoli is very thin so ...

At the end of the alveoli are capillaries, which are tiny blood vessels. Oxygen moves from the lungs to the bloodstream through these capillaries. In exchange, carbon dioxide moves from the blood ...

Cardinal David asks for prayers for Pope Francis who has been admitted to a hospital in Rome and developed pneumonia.