HowStuffWorks / Lee Dempsey

Stem Cell Basics

A stem cell is essentially the building block of the human body. Stem cells are capable of dividing for long periods of time, are unspecialized, but can develop into specialized cells. The earliest stem cells in the human body are those found in the human embryo. The stem cells inside an embryo will eventually give rise to every cell, tissue and organ 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 several types of stem cells, including:

  • Embryonic stem cells - Embryonic stem cells include those found within the embryo, the fetus or the umbilical cord blood. Depending upon when they are harvested, embryonic stem cells can give rise to just about any cell in the human body.
  • Adult stem cells - Adult stem cells can be found in infants, children and adults. They reside in already developed tissues such as those of the heart, brain and kidney. They usually give rise to cells within their resident organs.
  • Induced pluripotent stem cells (IPSC)- These stem cells are adult, differentiated cells that have been experimentally "reprogrammed" into a stem cell-like state.

So how do all these types of stem cells work? And what are their potential uses? Let's find out -- starting with embryonic stem cells.