Stem Cells

What Are Stem Cells?

You’ve probably heard about stem cells in the news and may wonder exactly what that scientific term means. Stem cells are the body’s master cells. Stem cells can renew themselves (a process called self-renewal), and they can also make a variety of other kinds of cells.

Stem cells are either embryonic stem cells or adult stem cells. In the lab, embryonic stem cells keep reproducing themselves until they’re coaxed into creating specific types of cells. In the body, these cells eventually disappear, so a human adult body no longer contains cells that can generate any kind of cell — at least not in the normal course of things. (Scientists can manipulate adult cells to become other types of cells.)


The main difference between embryonic and adult stem cells is their type of potency. Here’s a breakdown of the differences:


Embryonic stem cells: Embryonic stem cells are derived from three- to five-day-old embryos that are created for fertilization treatments but aren’t going to be used to try to start a pregnancy; in other words, these blastocysts have never been implanted in a woman’s uterus and will be discarded if they aren’t used for research. IVF doctors culture a fertilized IVF embryo in a culture dish until it develops to the blastocyst stage. Researchers extract the inner cell mass, which is then used to derive embryonic stem cells.

Embryonic stem cells are pluripotent, meaning they can give rise to any type of cell in the fully developed body. (Embryonic stem cells can’t create the placenta or umbilical cord tissues, but they appear to be able to generate any other type of cell.)


Adult stem cells: So-called adult stem cells are really stem cells in specific tissues whose job seems to be replenishing their particular tissues — or specific parts of their tissues — as needed. Adult stem cells also renew themselves periodically to ensure that a pool of stem cells is always available to generate specific cell types. So far, scientists have verified stem cell caches in several tissues, including bone marrow, the brain, fatty tissue (called adipose tissue), the liver, the reproductive system (both male and female), skeletal muscles, skin, and teeth.

Adult stem cells are generally multipotent, able to give rise to several kinds of cells in their home tissues. However, in their normal environments, adult stem cells don’t seem to generate cell types outside their particular tissues. Liver stem cells, for example, don’t generate heart cells, and brain stem cells don’t generate kidney cells.

Stem cell researchers have developed a technique for reprogramming adult cells in the lab to get them to act more like embryonic stem cells. These reprogrammed cells are called induced pluripotent stem cells (iPS cells), and they can be made from adult cells in the skin, fatty tissue, and other sources.


Scientists use various types of stem cells in the lab to gain a better understanding of how normal human development works and to look for new methods of treating a wide range of devastating human ailments. Stem cells in the bone marrow, for example, are routinely used to treat leukemia and other blood disorders, and similar techniques are being tested for other diseases involving problems with the immune system. As yet, no one has developed a safe and effective treatment using human embryonic stem cells, because the science itself is still young.  But many researchers expect to see several such treatments enter clinical trials (and eventually the market) at an ever-increasing pace.



[ Source: Stem Cells For Dummies by Lawrence S.B. Goldstein, Meg Schneider]
[ Images: Left shows a mesenchymal stem cell. Right llustration shows a human embryonic stem cell colony expressing insulin-like growth factor (IGF) receptors (red), surrounded by niche cells expressing fibroblast growth factor (FGF)receptors (green). Blue indicates the nucleus of all cells in the dish. (Credit: Image courtesy of McMaster University) ]