Liver regeneration

Regeneration is the capability of an organ to replace tissue mass after partial removal or injury. The normal adult liver is a quiescent organ exhibiting minimal replicative activity and, in fact, mitosis is observed only in approximately 1 in every 20 000 hepatocytes.

After partial hepatectomy (PH) the remaining hepatocytes can proliferate to restore the mass of the organ within days to weeks. In the rat, peak DNA synthesis occurs 24 h after PH, when approximately 35% of hepatocytes are actively involved in cell replication.

Mitosis follows DNA synthesis 6–8 h later, and during the course of regrowth most hepatocytes will have replicated at least once or twice. The replication of non-hepatocyte cells generally is delayed by approximately 24 h, but exhibits a similar synchronous pattern of DNA synthesis and mitosis as observed in hepatocytes. Сhristmas cactus care pruning https://cactus-christian.org/how-to-care.html.

During the regenerative process, there is an increase in mass resulting from cell proliferation of the remaining hepatocytes. In general, progenitor, or socalled stem cells do not participate in liver regeneration after PH, but are activated and differentiate into hepatocytes only after certain types of toxic injury. In addition, the proliferative response of hepatocytes to PH begins almost immediately.Once the original size of the liver is attained, hepatocytes revert to their non-replicative, quiescent state. Liver regeneration is actually a process of compensatory growth of the remnant liver and is not regeneration of the removed tissue.

In fact, the immediate early genes that are rapidly induced as liver cells exit from their normally quiescent state include many of the proto-oncogenes implicated in cancer growth. Their expression is independent of protein synthesis and appears to result from mitogenic stimuli. In contrast, delayed-early genes are expressed during the G0–G1 phase transition and are dependent on protein synthesis.

The entire regenerative process is a cascade of events that moves cells from G0 through G1 and DNA synthesis, through G2 to M phase and cell division, and is tightly regulated by both extrahepatic and intrahepatic signals. When the optimal ratio between functional hepatic mass and body mass is reached, the cells return to their resting G0 state.