How does the body replace its cells, and how often?

The fascinating biology of cell regeneration...
07 June 2024

RED BLOOD CELLS.jpg

Blood smear, blood cells

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Question

John wrote in to say,

'Why is it that the body replaces its cells every few years or so? It's not clear why this is beneficial from an evolutionary perspective? My old arm was working just fine!'

Answer

James Tytko took on John's question with the help of Nadia Rosenthal from Imperial College London...

James - Thanks John, you’ve touched on the fascinating phenomenon of cell regeneration. This is a critical biological process across all living organisms, and it’s my pleasure to introduce Professor of cardiovascular science Nadia Rosenthal from Imperial College London to explain further…

Nadia - Thanks James! Cells, like any complex machine, wear down over time: their DNA accumulates mutations, their component parts become damaged, or they are naturally lost in the process of bodily functions.

James - It follows, given that these cells wear out over time, we need to replace them somehow. Just take the 500 million skin cells sloughed off the body each day, for example.

Nadia - Exactly. Replacing aged cells is one way to ensure that there is a constant replenishment of old or dysfunctional cells with young healthy cells so they can continue to perform cellular functions properly.

Most of the 37 trillion cells in our bodies maintain the capacity to replace themselves by producing daughter cells from small populations of progenitors set aside for this process.  

Cell regeneration also happens if we've suffered an injury. Daughter stem cells may possess the ability to form a whole range of different cell types depending on what the body needs to replace.

James - Given the amazing variety of functions cells are responsible for in the body, not all of them regenerate in the same way: skeletal muscle cells last for decades, while your nerve and heart muscle cells are the same ones you had as a child. 

Nadia - Indeed, healthy cells only divide when necessary and the process is tightly controlled. Otherwise your arm wouldn’t keep its exquisitely choreographed functions – imagine if the overall blueprint was lost and it slowly turned into a cauliflower!

We don’t yet fully understand how this perfect replacement process works – but we know when it goes wrong, either in the case of cancer (uncontrolled cell proliferation), spinal cord injury or dementia (where no replacement of lost nerve connections occurs) or heart failure (in this case, lost heart muscle cells are replaced with scar).

Other animals such as starfish or salamanders do a much better job at regeneration and can grow back a whole arm, wouldn’t we love to know how to do that!

James - Thanks Nadia. To recap, as cells get older, they incur more damage which can lead to more mutations and more likelihood of things going wrong. Luckily, most of our cells have the ability to produce daughter cells from within, allowing us to maintain our critical bodily functions and adapt to changes in our environment.

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