Spare parts

[Fiona T]

Saw this good news story amongst all the doom and gloom on the BBC news site

https://www.bbc.co.uk/news/uk-scotland- ... t-61584096

If they can do a successful complete hand transplant, why don't they (can't they?) routinely offer limb transplants to amputees or people born with limb deformities?

Then I got to wondering about replacement bones - it would (to my simple mind) seem relatively straightforward to replace (e.g.) a badly shattered femur with a replacement - they already do hip replacement surgery - why not just whip out the whole bone and pop in a new one?

[Marc Meakin]

Saw this good news story amongst all the doom and gloom on the BBC news site

https://www.bbc.co.uk/news/uk-scotland- ... t-61584096

If they can do a successful complete hand transplant, why don't they (can't they?) routinely offer limb transplants to amputees or people born with limb deformities?

Then I got to wondering about replacement bones - it would (to my simple mind) seem relatively straightforward to replace (e.g.) a badly shattered femur with a replacement - they already do hip replacement surgery - why not just whip out the whole bone and pop in a new one?

Maybe not in my lifetime but it will eventually be able to 3D print limbs, organs etc.

[Mark Deeks]

I don't mean this flippantly, I just really have no idea what I'm talking about - how come livers and salamanders can regenerate, but most other things can't, and why can't we harness that power?

[Callum Todd]

I don't mean this flippantly, I just really have no idea what I'm talking about - how come livers and salamanders can regenerate, but most other things can't, and why can't we harness that power?

I don't think the biology of regeneration is very well understood yet. Pretty sure all animals with ability to regenerate whole body parts (rather than just skin and hair like we can) are invertebrates, so even with a full understanding of the process in salamanders and starfish and whatnot we're unlikely to ever work out how to regenerate limbs with bones in them, but perhaps organs (like livers) are a possibility. The heart has some regenerative capability too.

The ongoing study of how regeneration works is all about potential for cell division. A probable barrier to harnessing the power of regeneration is the 'potency' of our cells. Most adult mammalian cells are 'unipotent' (one potential: they can only be one kind of cell). Invertebrates like salamanders often have more cells that can differentiate into many different kinds of cell ('pluripotent', I think). So any technological innovation humans might make along the lines of generation will likely require us to harness human stem cells.

Interestingly, I remember reading once that some chemicals that cause tumours when injected into vertebrates (tumours being rapidly dividing cells) will cause new limbs to grow if injected into newts.

[Mark Deeks]

I think I'd rather be a newt. Also, how come if a salamander loses a leg, it grows a new leg, but only one? Why doesn't it grow two? How does a cell have the sentience to know what it can and can't be? Where's the blueprint?

[Callum Todd]

To take my very limited understanding and then simplify it even more: that's basically what DNA is. The sequence of amino acids/nucleotides/whatever spells out a sort of computer code that tells the sell what proteins to build like: 'if there's a leg here, do nothing. If there isn't, build one.'

[Mark Deeks]

Then how come potato has loads of DNA? Surely the options there are "grow more potato" and "do not grow more potato"?

[Callum Todd]

Not sure I understand the premise. Do potatoes have an usually high quantity of DNA?

The DNA thing was my attempt at answering your question about where the "blueprint" comes from, as that's what 'tells' an organism what proteins to make (like proteins that will make skin cells to heal your skin when cut, or that will make newt legs to grow a new leg if you're a newt who's lost one, or to... make more potato if you're a growing potato?). I don't think quantity of DNA necessarily corresponds with quantity of options, i.e. 'potency' of cells, but presumably the more stuff you need to make, the more DNA you will have.

[Ian Volante]

Not sure I understand the premise. Do potatoes have an usually high quantity of DNA?

Not sure about spuds specifically, but some plants have vast amounts of genetic material, sometimes caused by reduplication of their genome.

[Fiona T]

So the answer to my original question seems to be "because it's difficult surgery"

https://www.reddit.com/r/askscience/com ... s/c7c08ro/

[Ian Volante]

So the answer to my original question seems to be "because it's difficult surgery"

https://www.reddit.com/r/askscience/com ... s/c7c08ro/

I've not read that link (sorry), but it seems to me that it would be much easier to add a hand to an arm that already had one than it would be to add one to a deformed arm. In the case of deformity, there's no consistency, and it's likely that the relevant vascular and nerve systems would be inadequate.

[Fiona T]

So the answer to my original question seems to be "because it's difficult surgery"

https://www.reddit.com/r/askscience/com ... s/c7c08ro/

I've not read that link (sorry), but it seems to me that it would be much easier to add a hand to an arm that already had one than it would be to add one to a deformed arm. In the case of deformity, there's no consistency, and it's likely that the relevant vascular and nerve systems would be inadequate.

Yeah that makes sense. Plenty of amputees that would probably welcome a replacement hand/foot though!