How Stem Cells Work

by Stephanie Watson

Introduction to How Stem Cells Work

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This week, a group of London-based scientists requested official permission to begin a three-year study involving stem cells derived from human-cow hybrids. See more cloning pictures.

­Inside an ­embryo no bigger than the period at the end of this sentence are dozens of stem cells. Initially, these cells are blank slates, meaning that their fate is undecided. But they have great potential. Stem cells are pluripotent, which means that they can develop into every cell, every tissue and every organ in the human body. ­­ Their almost limitless potential has made stem cells a significant focus of medical research. Imagine having the ability to return memory to an Alzheimer's patient, replace skin that was lost during a terrible accident or enable a wheelchair-bound person to walk again. But before scientists can use stem cells for medical purposes, they must first learn how to harness their power. They can't treat disease until they learn how to manipulate stem cells to get them to develop into specific tissues or organs.

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­In this article, we will look at stem cells, find out how they work, discover their potential to treat disease and get inside the fierce debate surrounding their research and use.

Stem Cell Basics
A stem cell is essentially the building block of the human body. The stem cells inside an embryo will eventually give rise to every cell, organ and tissue in the fetus's body. Unlike a regular cell, which can only replicate to create more of its own kind of cell, a stem cell is pluripotent. When it divides, it can make any one of the 220 different cells in the human body. Stem cells also have the capability to self-renew -- they can reproduce themselves many times over.

There are two types of stem cells: embryonic stem cells and adult stem cells. Embryonic stem cells come from an embryo -- the mass of cells in the earliest stage of human development that, if implanted in a woman's womb, will eventually grow into a fetus. When the embryo is between three and five days old, it contains stem cells, which are busily working to create the various organs and tissues that will make up the fetus.

Adults also have stem cells in the heart, brain, bone marrow, lungs and other organs. They are our built-in repair kits, regenerating cells damaged by disease, injury and everyday wear and tear. Adult stem cells were once believed to be more limited than stem cells, only giving rise to the same type of tissue from which they originated. But new research suggests that adult stem cells may have the potential to generate other types of cells, as well. For example, liver cells may be coaxed to produce insulin, which is normally made by the pancreas. This capability is known as plasticity or transdifferentiation.

So where do scientists get the stem cells they use in their research? We'll look at two ways -- reproduction and cloning -- in the next section.

Full article How Stem Cells Work