system
Given the following post, respond as if you're commenting on Reddit:
human
How come the Liver is the only vital organ that can repair itself and grow back? What is the reason for this?
gpt
The distinction of the liver as the only organ that can repair/regrow is a bit misleading.  It is commonly cited as the prototypical self-repairing organ, but in actuality many parts of the body can constantly repair and renew itself.  The basal layer of the epidermis is a great example of a cell type that retains some stem-ness and is able to regenerate skin and provide compensatory responses to injury.  Similarly, adult stem cells are found in many other sites, such as the crypts of Lieberkuhn in the intestines, hematopoietic stem cells in the bone marrow, and even neural precursor cells in the brain.  Admittedly, we don't yet have a great understanding of the roles each of these cell types play in the regeneration/homeostatic process, but we do know that they are much more prevalent than previously thought.

With regards to the liver, it's important to note that true 'regeneration' is not occurring - rather, there is compensatory hyperplasia as the remaining liver tissues receive various chemical signals to proliferate and restore lost hepatic function.  Many other organs, including kidney, pancreas, adrenal glands, thyroid, and the lungs of very young animals, also demonstrate compensatory hyperplasia, but just to a less noticeable extent.  With this compensatory hyperplasia, the surgically resected lobes are not regrown - rather, the remaining lobes enlarge, such that function is restored without restoration of original form.  This is mediated by signalling molecules such as HGF, TGFa, EGF, TNF, Il-6, as well as hormones and neurotransmitters like norepinephrine, serotonin, insulin, thyroid and growth hormone.