The respiratory system (or ventilatory system) is the biological system that introduces respiratory gases to the interior and performs gas exchange. In humans and other mammals, the anatomical features of the respiratory system include airways, lungs, and the respiratory muscles. Molecules of oxygen and carbon dioxide are passively exchanged, by diffusion, between the gaseous external environment and the blood. This exchange process occurs in the alveolar region of the lungs. Other animals, such as insects, have respiratory systems with very simple anatomical features, and in amphibians even the skin plays a vital role in gas exchange. Plants also have respiratory systems but the directionality of gas exchange can be opposite to that in animals. The respiratory system in plants also includes anatomical features such as holes on the undersides of leaves known as stomata.
Famous quotes containing the word system:
“The system was breaking down. The one who had wandered alone past so many happenings and events began to feel, backing up along the primal vein that led to his center, the beginning of hiccup that would, if left to gather, explode the center to the extremities of life, the suburbs through which one makes one’s way to where the country is.”
—John Ashbery (b. 1927)