I’d hazard a guess that most people don’t know much about their spleen. I certainly didn’t, beyond vague ideas about filtering blood. I’d heard it mentioned as part of the immune system. But mostly, I’d heard about it from people who had accidents – skiing or mountain biking crashes – whose spleen had burst.
I think we don’t all learn what the spleen does because the organ defies a simple description. To me, it highlights the difference between evolution and engineering. The parts of a machine usually each serve one purpose, and we consider something clever if it does two things at once. In contrast, it’s pretty common for an organ to do several totally different things. Evolution doesn’t have the conceptual boundaries that an engineer might, and often solves problems by co-opting existing structures to new functions, so the body’s limited genetic and developmental code can get reused in surprising ways.
So it is with the spleen. The spleen indeed filters your blood, removing malformed or aging blood cells and platelets. It also has several specialized roles in the immune and lymphatic systems. Most important of these, the spleen gives us innate immunity to some dangerous bacteria by recognizing molecules on their surface. Without a spleen, you’re in danger of blood infections, and you have to get to a hospital quickly any time you have an unexplained fever. Luckily, we have vaccines against the most common of these bacteria that have saved many people’s lives (I’m up to date). Losing your spleen also increases the risk of certain cancers, which might be related to both its immune and blood filtering functions. Finally, the spleen stores blood cells, releasing them to help deal with things like changes in blood pressure or oxygen levels.
I’m not happy to have lost my spleen. It’s really the only organ that I lost full function of in this accident. I still have half a pancreas and one fully functioning kidney, but zero spleens. However, I haven’t given up hope:
Once in a while, when someone loses their spleen, little bits of what remains can lodge themselves in other parts of the bloodstream, and grow tiny new spleens: Splenunculi.
By the odds, I probably won’t develop splenunculi. But I like the thought of having them. Little lodgers working hard to fill the shoes of their absent predecessor. I won’t hold my breath, but I’ll be looking for them in my CT scans.