The point of it all: energy for cells
Every cell in your body runs on a slow, controlled burn. It takes in oxygen, uses it to release energy from food, and produces carbon dioxide as the waste. Cut off the oxygen and the burn stops within minutes; let the carbon dioxide pile up and the blood turns acidic. Breathing exists to keep oxygen flowing in and carbon dioxide flowing out — nothing more glamorous, and nothing more essential.
The whole of respiration is this exchange of two gases, carried out so reliably that you never think about it. A single calm breath at rest — the smooth, effortless pattern doctors call eupnea — is one small turn of a wheel that has to keep spinning every moment of your life.
Two halves of respiration
Doctors split respiration into two stages that happen far apart in the body. External respiration is the lung end: oxygen moving from the air sacs into the blood, and carbon dioxide moving the other way. Internal respiration is the tissue end: oxygen leaving the blood to feed a muscle or organ, and carbon dioxide leaving that tissue to be carried away. The blood is the shuttle that links the two.
Three words people mix up
Because these words sound interchangeable in daily speech, it is worth pinning them down once. In lung medicine they are three different links in one chain — and a patient can fail at one while another works perfectly.
- Ventilation — air physically moving in and out of the lungs, the bellows action of breathing.
- Gas exchange — oxygen and carbon dioxide trading places across the thin wall between air and blood.
- Respiration — the whole purpose: getting oxygen to cells and carbon dioxide away from them.