Stem cells are stirring great excitement in medical research. But, what are stem cells? Why are scientists so intrigued by them? And, what are some of the concerns about stem cell research?
When an egg is fertilised by a sperm to make a human embryo, the single fertilised egg cell divides millions of times to form the six billion or more cells that make up our bodies. Most of these cells have undergone a process called differentiation, which leads to them becoming specialised for a certain function. For example, neurons (nerve cells) are specialised to convey electrical messages around the body.
Stem cells play a critical role in normal growth and development by providing new cells for growth and for replacing and repairing used and damaged tissues. Stem cells differ from other cells in the body in three main ways.
- Stem cells are unspecialised. They have not developed into cells that perform a specific function (differentiation).
- Stem cells are capable of self-renewal. Once a cell has become specialised, it has a very limited capacity to produce new cells, and then only cells of the same type. Thus, if a muscle or blood cell is damaged, it cannot replace itself. Stem cells, however, are able to divide and produce copies of themselves and lead to self-renewal.
- Stem cells can differentiate. They can divide and produce cells that have the potential to become other more specialised cell types. These new cells and tissues are used to repair or replace damaged or diseased cells in the body. Stem cells from different tissues and from different stages of development can give rise to varying numbers and types of cells.