A good starting point for any scientist in any field is to acknowledge that there’s a lot that we don’t know. We don’t know, for example, why there is more matter than antimatter in the universe. We don’t know quite how the evolution of the dinosaurs panned out. And, perhaps most surprisingly of all, we don’t know quite how many organs the human body has or what all their functions are.

This January, researchers have announced that a brand new organ had been discovered in our bodies after it had long been mistaken for something else. Now, writing in the journal Nature, a group of researchers from the University of California, San Francisco (UCSF), have found that the lungs in mice have a hidden feature too – they help make blood.

Specifically, it appears the lungs produce over half of the platelets – the components that bind blood together to stop us bleeding out when we’re wounded – involved in circulation.

So not only do our breathing bags allow us to respire, but they also help keep our cardiovascular system full to the brim. Well that’s rather lovely of them.

That’s not all. The researchers also managed to identify a cache of stem cells – the type that can differentiate into almost any cell type with the right biological programming – that can transform themselves into blood cells.

Bone marrow is thought to be the primary source of such stem cells, so this new revelation suggests that if our bone marrow is damaged and unable to keep up with its regular blood cell manufacture, our lungs can step in to make up for the shortfall.

“This finding definitely suggests a more sophisticated view of the lungs – that they're not just for respiration but also a key partner in formation of crucial aspects of the blood,” senior author Mark Looney, a professor of medicine at UCSF, said in a statement.

A little caveat worth mentioning at this point is that this hasn’t been directly imaged in humans, but mice. Nevertheless, the biological workings of these little critters is surprisingly similar to that of humans, which is part of the reason why they’re used in so many medical-themed studies – so there’s a good chance human lungs also possess the same hidden features.

Using a remarkable technique allowing the platelets to fluoresce, the team were able to directly trace the paths of the mousey platelets, and found they were coming from within the lungs. The megakaryocytes – the platelet-producing cells – are also seen moving back and forth between the lungs and the bone marrow, depending on where they are needed the most.

“Perhaps ‘studying abroad’ in different organs is a normal part of stem cell education,” Looney added.