Stable cells and liver regeneration after partial hepatectomy
Stable cells normally divide slowly at rest but can divide rapidly when required, so the liver is able to regrow when part of it is removed.
Remember
Hepatocytes are stable cells: they divide rarely at rest but can re-enter the cell cycle rapidly after injury, so the liver regrows by hyperplasia once part of it is removed.
Memory aid
labile means always dividing, stable means on standby, permanent means finished
Use it to sort cells by how readily they divide.
Cells are often grouped by how readily they divide. Labile cells are short-lived and replaced all the time from stem cells (unspecialised cells that divide and mature into replacements), as in the gut lining. Permanent cells, such as neurones, have left the cell cycle for good, so they are poorly replaced after injury.
Stable cells include hepatocytes (the main cells of the liver) and renal tubular cells (the cells lining the kidney tubules). At rest they are quiescent, which means they sit outside the active cell cycle in a resting state called G0, and they divide slowly. When tissue is lost, the surviving mature cells are stimulated back into the cycle and divide quickly.
The liver regrows after a partial hepatectomy, which is the surgical removal of part of it. Signals released by the injured liver, such as cytokines and growth factors (chemical messengers that tell cells to divide), prompt the resting hepatocytes to re-enter the cycle. The result is hyperplasia, a rise in cell number, which restores the lost volume. The signals are normal growth signals rather than mutations, so the response is self-limiting: once the volume is restored the hepatocytes go back to rest and no tumour forms.
Hypertrophy is different: the cells get bigger but no extra cells are made, so it is not the main mechanism of liver regrowth.
Key facts
- Stable cells
- normally divide slowly at rest but can divide rapidly when required.
- Hepatocytes
- are classic stable cells, as are renal tubular cells.
- Labile cells
- are short-lived and constantly replaced from stem cells, for example the lining of the gut.
- Permanent cells
- are poorly replaced after injury, for example neurones.
- Liver regrowth
- occurs by hyperplasia, an increase in cell number, and stops once the lost volume is restored.
- Hypertrophy
- enlargement of cells without extra cells, so it is not the main mechanism of liver regrowth.
Exam traps
- Gut lining cells are labile: they divide at a high rate all the time, so they are the wrong example for a tissue that is usually quiet.
- Stable cells are normally quiescent and divide slowly, not continuously with high turnover (cells being replaced continuously), which is the pattern of labile cells.
- Permanent cells cannot replicate effectively after injury, so they cannot produce the rapid burst of mitosis (cell division) that follows tissue loss in stable cells.
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