The most simplest and used definition ofis that they represent the "building blocks" of the human body.
But why stem cells are so special, in comparison with all the others, more than 200 types of adult specialized cells from the structure of our tissues and organs?
All adult cells have a well established function or functions and therefore are considered specialized cells.
For instance: muscle cells have the primary function of generating movement, by contraction and relaxation; neurons are highly specialized cells responsible for processing and transmission of cellular signals. But none of these 2 type of adult cells can't fulfill other functions q.e. to secrete bile - only liver cells can do this
Stem cells are first of all unspecialized cells, but they have 2 defined and unique features: self-replication and cellular differentiation.
Self replication or self-renewal means the capacity of stem cells to give rise to a new population of cells identical with themselves. Thus it's possible to maintain for long term a pool of stem cells, responsible for providing new adult cells:
- to replace those which are periodically removed according to their life span (cells ageing) or
- those which are destroyed due to different insults (infections, trauma, different diseases or environmental injuries).
Differentiation capability represents the stem cells feature to divide and give rise to "daughter cells", with a higher degree of definition for their cellular functions (more specialized cells).
For instance: blood forming stem cells give rise to different type of blood cells: red blood cells (named also as erythrocytes), white blood cells (named also as leukocytes) and platelets (named also as thrombocytes).
For a better understanding of self replication and differentiation processes and their importance I'm giving you an example:
Human red cells are important component of the blood, responsible for carrying oxygen to the tissues and take up the carbon dioxide (CO2) resulting from their metabolism processes.
The life span of a human red blood cell is 110-120 days and then, they are destroyed mainly in the spleen. Those red cells, have to be replaced by a new generation in order to maintain the normal value of red cells in the blood.
The replenish process is done based on the new adult red cells released from bone marrow as a result of blood forming stem cells differentiation into more adult and specialized cells belonging to red cells lineage.
At the same, if the pool of appropriate number of stem cells would not be maintained by self replication also known as renewing process, no other stem cells for future new cycles of cells differentiation would be available.
Stem cells are the first cells which appear after the moment of conception. They are the foundation of all types of cells, tissues and organs in the human body, all stemming from these unique cells.
During entire our life, all renewing, replenishing, internal repairing and regeneration processes are done based on adult stem cells, which are present in many tissues.
But in some tissues stem cells have to divide regularly, while in others only in certain situations. The number of tissue specific stem cells as well as the repairing and regeneration capacity are also not the same for all tissues and organs. These depends on the regular and the special conditions tissue demands.
For instance: gut has a high level of cellular turn over, meaning a high demands for replacing the worn out or damaged cells. Therefore also the specific tissue somatic stem cells has to divide regularly to meet this demand.
This "internal restoration system" can cope with the physiological requirements of tissue renewal. Also, in the recovery stage after infections, trauma, diseases or environmental injuries, it has an important role for regaining the body health.
By the new stem cells based therapies the researcher are proposing to use the unique features of these cells to support and boost the internal regeneration, especially in those tissues where is exceeded as a result of serious or chronic insults.
Although we are in an early stage of the emerging field of regenerative medicine some encouraging results were already published as a result of preclinical or clinical research activity.