Stem cells types and applications

STEM cells are life itself!

Stem cells are cells that underlie the formation of all tissues and organs. They are characterized by 2 basic properties: the capacity to self-replicate and the capacity of cell differentiation. Self-replication is the self-renewal or the stem cell capacity to give birth to a daughter cell identical to itself. Differentiation is the stem cell ability to give rise to different daughter cells, more specialized, capable of exercising only certain well defined functions in the body. (e.g. The hematopoietic stem cell is able to self-replicate by asymmetric division - giving birth to daughter hematopoietic stem cells, identical to itself - and at the same time, to differentiate itself - giving birth to a more specialized daughter cell, called lymphoid progenitor cell or myeloid progenitor cell, which, through successive differentiations, should then generate the 3 types of blood cells, the erythrocytes, the leukocytes and the platelets, see Figure 1.)

Stem cells can be ranked according to the types of specialized cells that they can generate in more categories - totipotent stem cells are the first cells that develop after the egg fertilization by sperm, present only in the embryo stage until the age of 5 -6 days (these cells can give rise to all the over 220 cell types in the human body), pluripotentential stem cells, present in the embryo of more than 6 to 8 days and the fetus, multipotent stem cells (including hematopoietic stem cells and somatic stem cells) present in the fetus, infant and adult. (see Figure 2.)



Why are stem cells necessary?
In intrauterine life of the embryo and fetal development is done starting from the stem cells.
After birth, every cell in the body has a genetically pre-determined life time. It is therefore necessary to regularly replace cells that are characterized by a "programmed death" (e.g. Red blood cells normally have a lifespan of 120 days) or because of the action of various assaults on the body (e.g. traumas, infections, toxins).
An example of the way this periodic "renewal" of body cells takes place is haematopoiesis. All the 3 types of cells in the blood (red blood cells, leukocytes and platelets) originate from a sequence of cellular differentiations from a single cell, namely the hematopoietic stem cell.
After birth, hematopoietic stem cells are present only in the bone marrow and only very poorly in the peripheral blood and they are responsible for the periodic replacement of blood cells, a process called haematopoiesis.