British Sign Language Glossaries of Curriculum Terms

BSL Environmental Science Glossary - Exchange surface definition

Definition: The exchange surface is where oxygen and carbon dioxide are exchanged in the respiratory system in mammals, no matter what their size is, mouse, human or elephant. The body needs to expel CO₂, and the environment outside the body is conducive to the passive exchange of CO₂. The process is the same regardless of the size of the mammal; an elephant may have big lungs while a mouse has tiny ones, but the exchange system and surfaces are the same. The environment and the animal are in sync with each other. The system matches the environment in pressure and can use passive diffusion to work. Looking at how breathing works, at the very end of the bronchi in the lungs, there are bubble-like structures called alveoli, which are completely surrounded by many tiny blood vessels and capillaries. So when O₂ is breathed in, it diffuses through the alveolar membrane to the bloodstream, which is taken up into the body. The reverse happens for CO₂; it needs to be expelled, so the same process occurs in reverse so the CO₂ can travel out of the lungs to be exhaled. This exchange of O₂ and CO₂ is concurrent and has evolved to exploit the gases efficiently from the environment outside the body for use inside the body.