Concept preview

What you will be able to do

1. 01Trace the pathway of air from the nasal cavity to the alveoli, naming each structure in order.
2. 02Distinguish the conducting zone from the gas-exchange (respiratory) zone and give the role of each.
3. 03Describe the diaphragm and intercostal muscles and where they sit around the lungs.
4. 04Explain how alveoli are adapted for efficient gas exchange (thin, moist, huge surface area, rich capillary supply).

Every cell in your body is a tiny furnace, quietly burning glucose with oxygen to release the energy that keeps you alive, and every furnace produces waste — in this case carbon dioxide — that must be carried away before it poisons the tissues. The job of the respiratory system is to solve both halves of this problem at once: to draw fresh oxygen out of the air and hand it to the blood, and to collect waste carbon dioxide from the blood and breathe it back out into the atmosphere. To manage this, air is funnelled along a branching pathway that begins at the nostrils and ends, millions of tiny chambers later, in microscopic sacs where the actual swap of gases takes place. Understanding breathing means following that pathway step by step, because every narrowing, fold and branch along the way has a purpose. Biologists usually split the route into two parts: the conducting zone, the plumbing that merely carries, warms and cleans the air, and the respiratory zone, the delicate surfaces deep in the lungs where oxygen and carbon dioxide finally cross between air and blood.