Smoking, lung disease and gas exchange
Biology · Key Stage 3 · The School
What smoke does on the way in
Cigarette smoke carries tar, carbon monoxide and other harmful chemicals. TAR is sticky. It coats the airways and the alveoli, the tiny air sacs where gas exchange happens. It also damages the tiny hair-like CILIA that normally sweep mucus and trapped dirt out of the airways.
Losing cilia means losing a defence
Without working cilia, mucus and the dirt trapped in it no longer clear away. It builds up in the airways instead. This is a major cause of a smoker's constant cough. Coughing becomes the only way left to shift what the cilia used to remove on their own.
Alveoli damage reduces surface area
Long-term smoking can damage and break down the walls of the alveoli. Many small air sacs merge into fewer, larger ones. This is called EMPHYSEMA. Fewer, larger sacs mean far less total SURFACE AREA for gas exchange. Surface area decides how much oxygen can cross into the blood at once. This damage does not heal, because destroyed alveoli do not grow back.
Gas exchange depends directly on surface area. More surface means more places for oxygen to cross into the blood at the same time. Healthy lungs have a huge total surface area, built from millions of tiny sacs rather than a few big ones. Many small sacs pack far more surface into the same lung space than a few large ones would. Emphysema works against this design. It merges sacs and shrinks the total surface. So the same lung space can now take in far less oxygen with each breath. A person with emphysema gets breathless doing things that used to be easy. Their lungs have not shrunk. What is left just moves far less gas per breath than it once did.