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Is radiation why we have stem cells inside our bones?

By thor - Posted on 14 December 2013

pic: Radiation by Gale and LaxI have been reading the book Radiation by Gale & Lax, which is a popular science book on the topic. I am reading this book in an effort to improve my own writing and communication skills for when I have to engage the public about radiation topics. I recommend this book to any one interested in learning more about radiation. It is a level-headed account and in no way sensational.

Through my experience with Nadia's Quest (my daughter is presently in bone marrow failure and needs a bone marrow stem cell transplant) I have learned a lot about bone marrow and stem cells. These two topics merged for me last night when I was reading this book.

Mammals produce blood cells using stem cells inside bone marrow. The bone marrow is like a blood producing factory, that continually makes different types of blood cells that not only keep blood circulating in your body, but are also integral for our immune systems to function. Many people are surprised to learn that our bones are not solid all the way through. Inside our bones are our blood cell factories - our bone marrow. Next time you by a steak from the butcher, notice that the centre of the bones are red - this is the marrow!

Gale & Lax put forward a theory in the book. They emphasize that this is a theory and not a fact. We live in a bath of background radiation, and stem cells are especially susceptible to damage from radiation. Our stem cells are within our bones, fish have them in the kidneys. Why the difference? They suggest Radiation!

We are all familiar with x-rays. The reason bones show up so well is because they more effectively stop radiation passing through the body, casting more of a shadow than the surrounding soft tissue. By placing these sensitive stem cells within bone, the hard bony shell acts as a shield from background radiation. Fish, on the other hand, are well shielded from background radiation already because they live in water, so background radiation from the sky and the soil have a good chance of being absorbed in the water instead of exposing the fish. Consequently, their sensitive stem cells do not need to be shielded by bones, and reside in the liver. It is likely that when mammals crawled out of the sea, over time Evolution moved these sensitive stem cells to within the bone. Protecting these stem cells help reduce cancer incidence and allows reproduction - Evolution in action!

It is interesting to note that dolphins and whales have their blood producing stem cells in their bone marrow. Why is this the case when they too live in water? Well, maybe because these mammals recently (relative to Evolutionary time frames) crawled back into the sea after Evolution moved the stem cells to the bones when they were on land.