Your body has many different types of cells (more than 200 to be more exact) each geared toward specific functions. You have skin cells and blood cells, and you have bone cells and brain cells. All your organs comprise specific cells, too, from kidney cells to heart cells.
Stem cells have potential
Your cells didn’t start out knowing how to come together to form your bones, heart or blood; they begun with more of a blank slate. These completely undifferentiated cells can be found during gestation, or the time the baby is in the womb, and are called embryonic stem cells. These early stage stem cells are master cells that have the potential to become any type of cell in the body.
First isolated in 1998, there is a lot of controversy around acquiring embryonic stem cells. Thankfully, we can also acquire stem cells that form just a little bit later down the road, like in the umbillical cord. These stem cells, known as adult stem cells, stay with us for life. (Later, we will learn why not all adult stem cells are equal.) Adult stem cells are more limited in the types of cells they can become, something known as being tissue-specific, but share many of the same qualities. Hematopoietic stem cells (Greek “to make blood” and pronounced he-mah-toe-po-ee-tic) found in the umbilical cord's blood, for instance, can become any of the different types of blood cells found in the body and are the foundation of our immune systems. Another example is mesenchymal (meh-sen-ki-mal) stem cells, which can be found in the umbilical cord tissue and can become a host of cells including those found in your nervous system, sensory organs, circulatory tissues, skin, bone, cartilage, and more.
Stem cells proliferate
To recap, we have certain types of stem cells that can become a variety of different cells—they are like the renaissance men of cells—but there is one more thing that makes stem cells special. This has to do with how they replicate themselves.
The body has two ways to create more cells. The first is usually taught in middle school science. Known as cell division, it’s where a cell replicates within its membrane before dividing into two identical cells. Cells do this as needed for regeneration, which we will touch on in a second.
The other way the body creates more cells is through its stem cells, and stem cells do things a little differently. They undergo what is called asymmetric division, forming not one but two daughter cells: one cell often an exact replica of itself, a new stem cell with a relatively clean slate, and another stem cell that is ready to turn into a specific type of cell. This trait is known as self-renewal and allows stem cells to proliferate, or reproduce rapidly.
Through these two means, we are always producing more cells. In fact, much of your body is in a state of constant renewal because many cells can live for only certain period of time. The lifespan for a cell in the stomach lining is about two days. Red blood cells, about four months. Nerve and brain cells are supposed to live forever. This is why these cells rarely regenerate and take a long time if they do.
Stem cells are regenerative
Different cells have different life cycles, and many are constantly regenerating, but when damage occurs and the body needs to come up with a new supply of cells to heal itself, it relies on the stem cell’s ability to quickly create more cells to repair the wound. Herein lays the potential for the introduction of new stem cells to enhance or be the driving factor in the healing process.
Scientists first found ways to use stem cells in bone marrow, and following this discovery, the first stem cell transplant was performed in 1956 via bone marrow between identical twins. It resulted in the complete remission of the one twin’s leukemia.
This and all other stem cell therapies since involve introducing new stem cells into the area to encourage the healing process. Often, the stem cell will create a particular type of cell simply because it is in proximity to other cells of that type. Unfortunately, researchers still had a ways to go before they could use stem cells from unrelated persons.