How can we grow a brand new windpipe? Or a heart? In this lesson, we’ll learn about embryonic and adult stem cells and how scientists are using them to give people a new lease on life.
What Are Stem Cells?
Imagine growing a windpipe in a lab. Imagine creating this windpipe from scratch for a little girl who was born without one. Now, you can stop imagining because science has been going in this direction for a long time.
It’s really super exciting. Doctors and scientists have developed ways to collect a few specialized cells originally from this little girl and grow them under super special conditions to create a trachea for her, even though her own body had never made one in the first place.Creating and growing organs in a Petri dish is no small feat. Science is making leaps and bounds in figuring out the best way to do this, using a person’s own cells.
Specifically, this is done using stem cells. Stem cells are cells with the ability to differentiate into many different cell types. Not all cells are lucky enough to be stem cells.
Stem cells are special.Stem cells can continually divide for a long time into identical copies of themselves. This is called self-renewal.
However, if they get the right signal from their environment, they can also differentiate into specific cell types. Differentiation is simply when one cell of a nonspecific cell type turns into a specific cell type.But before we talk about the types of stem cells that make this possible, we need to first brush up on human development.
Let’s talk about a bigger phenomenon. Forget about a windpipe. How do we create a heart? Or a bladder? An entire human body with different organ systems? Remember that life starts out as a single egg cell that becomes fertilized.This one fertilized egg then goes through several divisions to become an embryo and eventually grows into a multicellular human being with several different tissues and organs. So, the main question in development here is, ‘How do we go from one single cell to trillions of different cells that make up the human body?’The answer, of course, is complicated. We can begin by revisiting what happens after a human egg is fertilized by sperm.
It will divide and grow to form a blastocyst, which is an early embryo composed of an outer layer of cells, known as the trophoblast and a mass of internal cells, known as the inner cell mass.Now, it’s these cells in the inner cell mass that will eventually divide to become the embryo and then a real live baby with 10 tiny, perfect toes. What’s really cool about these cells in the inner cell mass is that they are one type of stem cell, capable of differentiating into any type of human cell. Let’s look at the different kinds of stem cells and where they’re located.
Embryonic Stem Cells
Embryonic stem cells come from exactly where they sound like they come from – an embryo. A really early embryo has totipotent stem cells that are able to differentiate into any type of cell of the placenta or the embryo.
These early embryonic stem cells only exist early in development – right after an egg is fertilized by a sperm. You can think of totipotent as meaning this fertilized egg has the ‘total’ potential to become any cell imaginable.A few cell divisions later, the embryo forms the blastocyst that we talked about earlier. At this point in time, the stem cells are no longer totipotent. Inside the inner cell mass of this blastocyst, there are embryonic stem cells known as pluripotent.
Pluripotent stem cells are able to differentiate into any cell in the human body, but not the placenta. That means that these pluripotent stem cells are the ones that will go on to form your muscle cells, your nerve cells and grow you a nice set of ears… you get the picture.Scientists know there’s a lot of power behind these types of embryonic stem cells. Imagine an unspecified cell that can become anything you want it to be. These embryonic pluripotent stem cells also grow really well in the lab. However, a lot of research still needs to be done to understand exactly how to grow and use these cells both correctly and to their fullest potential.
In addition, there have been some ethical barriers to harvesting embryonic stem cells, and this has stalled progress in this research field.
Adult Stem Cells
Now, what happens when an embryo grows into a baby that is born? What happens when this baby becomes an adult? Are there any more of these stem cells?Well, yes and no. Adults and babies have stem cells, but they are no longer pluripotent. Adult stem cells are known as multipotent.
Multipotent stem cells are able to differentiate into many different cell types, but not all. You can remember this because ‘multi’ means ‘many,’ but it’s not as many as a pluripotent cell.Because a multipotent stem cell can become just any cell, the adult human body has to have different types of these multipotent stem cells in different locations. Their normal function is to replace cells that the body needs. They will differentiate when they receive a signal that the body needs a specific type of cell.Adult stem cells are found in different parts of the human body, but they are hard to locate, and therefore, they’re harder to harvest than embryonic stem cells. They tend to be able to differentiate into cells similar in type to their location.
For example, stem cells in your bone marrow can differentiate into bone or cartilage tissue.Adult stem cells have a great potential therapeutic value that science is eager to use. Let’s go back to the little girl who was born without a windpipe. Using her own stem cells, scientists were able to grow her one by making these cells differentiate into tracheal cells. Because this new trachea was made from her own cells, there wasn’t this chance that her body would reject it like a normal organ transplant.In a similar way, adult cardiac stem cells can be used to grow new tissue to repair damaged tissue following a person’s heart attack.
Scientists are working full-speed to uncover the potential behind these special cells.
Let’s review. In this lesson, we talked about how some cells are unspecified, but have the ability to become different types of specific cells. These are stem cells, or cells with the ability to differentiate into many different cell types.
Differentiation is simply when one cell of a nonspecific cell type turns into a specific cell type.Totipotent stem cells are found in a fertilized egg early in development and are able to differentiate into any type of cell of the placenta or embryo. These are a type of embryonic stem cell, but they do not exist for long. After some cell divisions, there are pluripotent stem cells, which are found in the inner cell mass of the blastocyst and are able to differentiate into any cell in the body, though not of the placenta.After a human being is born, it now has multipotent stem cells, which are localized all over the body and are able to differentiate into many different cell types, but not all.
These are known as adult stem cells. Scientists have started to use embryonic and adult stem cells in developing therapies to disease and cancer, as well as recreating tissues and entire organs. We’ve only scratched the surface of their medical potential.
Once the lesson is finished, you should be able to:
- Define stem cells, self-renewal and differentiation
- Summarize how a single cell turns into a human being
- Recognize the differences between totipotent cells, pluripotent cells and multipotent cells
- Understand the potential of stem cells in disease therapy and growing new tissue or organs