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Related to my earlier question, "How does the human liver regrow?", am curious as to why the liver is the only major organ that has this capability?

Why is it that other major organs, such as the heart and lungs etc are not able to regrow in the same fashion?

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  • $\begingroup$ Would you be opposed to changing "part" in your title to internal organ? I believe that is what you mean. Also, how would you consider the GI track in your clasification of major? $\endgroup$ – Atl LED Aug 27 '13 at 20:15
  • $\begingroup$ @AtlLED I am not opposed at all to any constructive edits, such as you suggest. I am not 100% sure about the 'GI track'? $\endgroup$ – user3795 Aug 27 '13 at 20:55
  • $\begingroup$ The GI, or gastrointestinal tract, is all the machinery that helps you eat and digest things. Esophagus, stomach, small and large intestines, that sort of thing. $\endgroup$ – Resonating Aug 28 '13 at 2:55
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    $\begingroup$ @JeremyKemball thank you, I just did not know what GI stood for in this context. $\endgroup$ – user3795 Aug 28 '13 at 6:57
  • $\begingroup$ @AtlLED yes, now thatI know what GI stands for, yes, (but isn't the GI track a system?) $\endgroup$ – user3795 Aug 28 '13 at 6:58
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Maybe it is due to two factors:

  1. The liver is one of the few solid non-tubular organs. If a tubular organ is damaged, all the layers that composes it must regenerate. This layers usually have different cell types, which is always nasty for regeneration since some of them may be formed by specialized tissue (for instance, myocytes are very difficult to regenerate. If the organ has a muscle layer, such as the esophagus, regeneration will be more difficult). Furthermore, damage in a tubular organ usually involves perforation, which will disrupt its function even if the injure isn't big.

  2. Hepatocytes are pretty undifferentiated cells. They are basically enzymatic sacks with some vacuoles and mitochondrion, but they remain as your typical animal cell. They have a regular nucleus, they don't have any cytoskeletal adaptation and their vacuoles don't compose the most part of their cytoplasm (in a healthy liver). Cells with so little morphological specialization usually regenerate with no problem. Plus, the liver itself is constantly exposed to chemical damage due to toxins, drugs and other chemical compounds that may be present in the diet. This situation is special and don't apply for any other organs, with the exception of the kidneys (which, in fact is a very complicated tubular organ).

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    $\begingroup$ thank you for the answer! Do you have some references to add? $\endgroup$ – user3795 Aug 28 '13 at 11:09
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    $\begingroup$ stembook.org/node/512 This is a complete article describing all the embrionic development of the liver and also has some information about liver regeneration. I hope that is enought. $\endgroup$ – Miguel Ángel Naranjo Ortiz Aug 28 '13 at 11:23
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    $\begingroup$ I'm sure that the structure of the organ is important, but even so, liver growth in the lab requires a scaffold and doesn't regenerate from cells alone. I think the liver cells might regenerate more easily because of their role in detoxifying the blood - they probably die more frequently and need sometimes replacement even in segments of the organ. $\endgroup$ – shigeta Aug 28 '13 at 17:01
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It helps to think about why it's beneficial for an organ/tissue to regenerate. The liver is your main detoxifying organ. It does this by chemically modifying external (and internal) molecules to counter their possible bad effects or simply to be able to excrete them. This role brings liver cells in harms way. Take paracetamol for example. It is recognized as a foreign compound and detoxified mainly in the liver. If you overdose like many unfortunately do, liver cells are the first to die. So, to keep up your defenses the body has activated regeneration in liver cells but not in many other parts of the body that are more safely tucked away.

That said, many other organs and tissues in the body constantly regenerate too. The intestinal tract constantly produces new surface cells from stem cells that lie deeper down in the organ because it also is on the front lines just like liver cells. Something similar is true for the skin but of course skin and gut are both external organs and therefore closer to our environment. The liver is not far off, because it is among the first organs to receive blood from the intestine.

So even though it is possible to induce regeneration in many cells of our bodies artificially as induced pluripotent stem cells have shown, evolution has switched this on only in a few of our cell types which require more renewal than others, hepatocytes included.

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