About Stem Cells
What stem cells are?
Stem cells are the predominant cells of the human body. They have two characteristic properties which distinguish them from most cells of the adult organism. First, under certain circumstances, they have the ability to renew themselves and give rise to a large number of their copies with exactly the same properties. Second, the stem cells have the capacity to differentiate into different cell types. They are the source of all types of cells (hematopoietic cells, cells of our immune system and cells structuring almost every organ and tissue).
Stem cells have three stages in their life:
A. Embryonic stem cells
The first step in human development is when the fertilized egg or zygote begins to divide to generate stem cells called embryonic. These cells were characterized as pluripotent because they can differentiate into any cell type of the 200 present in our body.
Seven days after fertilization, embryonic cells form a sphere called a blastocyst. At this stage of blastocyst there are two kinds of cells. Embryonic cells inside the blastocyst create an inner cell mass, which will then give the body of the embryo. In the housing of the blastocyst there is trophoblast, which will then be converted in the placenta. Stem cells at this stage of blastocyst are called pluripotent, i.e. can be converted to almost any cell type in the human body. The isolation of such cells for future purposes would cause disruption in the fetus, which cannot be implanted in the uterus and of course dies. After the eighth week of development, the embryo is now called a fetus and has already begun to take human shape. Stem cells at this stage are responsible for the development of all tissues before birth. The stem cells of this step are also pluripotent because they can still be converted to almost any cell type in the human body.
B. Stem cells from umbilical cord blood
The umbilical cord carries blood from the placenta to the fetus. This cord blood is rich in nutrients and oxygen. The cord blood is also rich in stem cells, called umbilical cord blood stem cells. These cells are genetically identical to the child to be born. These precious stem cells did not differentiate during embryogenesis -(they did not manage to form tissues and remained in placental blood and umbilical cord blood). The stem cells of this step are multipotent, which means they can be converted into various kinds of cells, but not all.
C. Adult stem cells
Stem cells transferred to the fetus via the umbilical cord will be stored in various spots in the body in order to repair damages that will be generated throughout our adult life. The main spot of storage of stem cells, the “home” on the human body is the bone marrow. Note that there are many types of adult stem cells in humans. The stem cells of the bone marrow are specifically hematopoietic (forming all cell types of blood) or mesenchymal (form bone, cartilage, adipose tissue, etc.). Stem cells exist even in the brain, without knowing their capabilities, an open area of research. The stem cells at this stage are also multipotent, which means that these can be converted into various kinds of cells, but not all.