Tissue Renewal without Stem Cells

Some differentiated cell types like beta cells of the pancreas or hepatocytes of the liver can divide to renew and regenerate the tissue without using stem cells. This is interesting because differentiated cells have restricted cell division capacity and cannot replenish the entire organ.

The beta cells are the insulin-producing cells present in the islets of Langerhans. Loss of these cells is responsible for type I diabetes. However, the islets of Langerhans do not contain any specialized stem cells that can replenish the beta cells.

Therefore, the pre-existing beta cells undergo simple duplication to compensate for the loss of cells.

Similarly, hepatocytes in the liver are responsible for metabolic regulation and have a one-year life span. After this, they self-renew, producing more new hepatocytes.

Both of these processes, cell proliferation and cell death, are well regulated by homeostasis to maintain the size of the liver.

For example, when two-thirds of a rat liver is  surgically removed, the hepatocytes in the remaining section quickly multiply to regenerate a normal-sized liver in just two weeks.