Biology
Regenerative Capacity of the Human Liver
Quick fact
In a partial hepatectomy, removing two-thirds of the liver triggers a dramatic regenerative response: the remaining cells re-enter the cell cycle, and within about two weeks the liver regains its original mass and function.
Why this is interesting
Your liver can grow back to its full size even if you lose up to 70% of it. But what signals tell the liver cells to start multiplying?
Read the full explanation
Understanding Regenerative Capacity of the Human Liver
Imagine your liver is a construction crew with a blueprint for a building. If you bring in heavy machinery and knock down part of the building, the crew will rebuild it to exactly match the original plans. Similarly, when liver cells (hepatocytes) are lost due to injury or surgery, the remaining healthy cells receive a signal to switch from their normal 'resting' state (called G0) into active division. They replicate their DNA and divide, producing new hepatocytes to replace the lost tissue. This process continues until the liver reaches about its original size, and then a 'stop' signal is received, preventing overgrowth. The liver is unique because it can regenerate in this precise way, not by growing a new lobe, but by enlarging the remaining lobes to fill the space.
A deeper explanation
The regenerative process is orchestrated by a complex network of signaling pathways. After liver tissue is removed, a cascade of events begins. First, the body releases pro-inflammatory cytokines (like TNF-α and IL-6) that prime the hepatocytes, making them responsive to growth factors. The key growth factor is Hepatocyte Growth Factor (HGF), which is released by hepatic stellate cells and other non-parenchymal cells. HGF binds to the c-Met receptor on hepatocytes, activating proliferation pathways like the MAPK and PI3K/Akt cascades. Other growth factors such as epidermal growth factor (EGF) and transforming growth factor-alpha (TGF-α) also contribute. The hepatocytes undergo one or two rounds of division, and in parallel, other cell types (bile duct cells, Kupffer cells, and endothelial cells) also proliferate to rebuild the liver architecture. Once the liver mass is restored, mechanisms including the protein TGF-β inhibit further proliferation, establishing a negative feedback loop. This ability is essential for recovery after surgical resection for tumors or for living-donor liver transplantation, and it is a prime example of organ regeneration in mammals.