Eli5: if our bodies are able to form entire human beings from scratch, why can’t it grow back organs that have been amputated?
In: Biology
We can, at a cost. It’s called Regenerative Medicine.
A long time ago in our evolution we probably could regenerate entire limbs or organs, but the ones that quickly closed wounds with clotting and scarring outlived the ones that left wounds open to regenerate (probably died of infection).
Doctors are using what is called extracellular matrix (**ECM**, a scaffold made of cells within the body, or artificially extracted from pig bladders) to create a regrowth medium to entice stem cells (your body’s “I can be anything” cells) to regrow tissue. The matrix promotes vessel growth, and the stem cells fill in the gaps with tissue.
Kidney damage? Remove the damaged tissue, Put ECM at the site, and your body uses your own DNA map and surrounding tissue to regenerate your kidney to specifications, following it’s own blueprint.
The costs:
1. Wound must be left open, so vastly increases the danger of bacterial infection.
2. It takes a very long time to regenerate some things. 6-9 months for an organ. A human can live hours without a liver, for instance. Even a partially donated liver is a better option, because they grow back.
3. We are still figuring it out, so the technology is in it’s infancy. Vets do use it on animals, and it’s quite successful.
Have a read. Warning, **not ELI5**: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9973391/#:~:text=Discarded%20human%20donor%20organs%20can,for%20organ%20engineering%20using%20hPSCs.
Vets: https://www.sciencedirect.com/science/article/abs/pii/S1534751604000423
Human successes: https://www.popsci.com/scitech/article/2008-05/man-regenerates-finger/
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