Science Questions

Macrophages can clean up debris in the lungs. One of your guests the other week said that these phages can help the spread of lung cancer. How can this be? Ian

That's a very good question. Macrophage literally means 'big eater' and are giant cells that do everything you might imagine a white blood cell would do. They have long rippling membranes that they extend like feet. When the find something that they want to eat, they extend these feet around the substance, engulf it and excrete lots of digestive chemicals into the substance and break it down. When we breathe in, we inhale millions of tiny particles of dust, chemicals and other substances. As they travel towards our lungs, they form a type of whirlwind and get stuck on a sticky layer of mucus on the edge of our windpipe. There are also lots of tiny hairs on the edge of our windpipe, which beat continuously and waft the mucus back upwards. Some particles obviously get trapped or go further in than normal. The macrophages act like hoovers and try to clean these up. However, sometimes the macrophages get a bit frustrated when they can't break them down, and so the particles get added back into the mucus to be either spat out or swallowed. It is interesting to note that people who smoke not only have higher rates of lung cancer, but also bowel cancer. It isn't immediately obvious why this is, but it's due to many of the particles being swallowed instead of spat out.

March 2005