My Liver Grows Back? : Liver Regeneration
It is well known that the liver regenerates. In fact, this has been known since the time of the ancient Greeks. Prometheus, was a character in Greek mythology, who was condemned to be tied to a stone after he attempted to steal sun from the gods. Every night, he was destined to have a crow eat his liver. His liver would grow back during the day, and then at night, he would undergo partial resection by the crow! This is early evidence of the understanding of the liver's unique ability to regrow. After that, as far as we know it was not until the late 19th century that Canalis carried out the first scientifically motivated partial liver resection. By 1894, liver regeneration had been documented in rats, mice, rabbits, and dogs. Over a century after that, we are still unclear to the exact mechanism involved in initiating that process!
In the early part of the 20th century, two scientists detailed a simple procedure in rats whereby a reproducible two-thirds liver resection could be performed. Interestingly, the liver regenerated within 5 to 7 days. This was a consistent feature, and allowed for continued experimentation in a controlled model. This model has been used by hundreds of laboratories that investigate the phenomena of liver regeneration.
The whole idea of the liver regrowing is interesting. Liver cells in the adult normally do not undergo division. Just like most cells in the adult, they are quiescent ("non-dividing"). However, unlike most cells in the adult, liver cells can be "triggered" into growing again. Any injury, whether it be toxin, infection, or surgical, will induce a response in these cells that is characteristic, and controlled. Within minutes of injury to the liver, the liver cells (hepatocytes) are induced to grow.
In the setting of surgery, when the liver has no previous injury to it, the cells initiate growth in a fairly consistent and specified pattern. While the term regeneration has been used, the liver does not actually re-grow the removed lobes - rather, the remaining liver gets larger. The cells not only grow in size, but they divide-increase in the number of liver cells. This is so remarkable, that even in the adult when half of the liver is removed, the liver reconstitutes its original size within 2 to 6 weeks. During that time, it is remarkable to appreciate that the remaining liver is doing two things: not only is it regrowing, but also it is actually continuing to function as the metabolic engine of the body.
In patients who have previous scarring of their liver (cirrhosis), whether it be from alcohol, virus, toxins, or other disease, the growth response is not so robust. This is because the scar in the liver, and the chronic disease-state of the liver prevent there from being a strong growth response. It is important at this time, to take a step back and understand how a diseased liver becomes scarred; scarring of the liver is commonly called cirrhosis.
