Stem cells are the origin of life and forerunners of modern medicine”

Types and tasks of stem cells

All-rounders with special properties

There are various types of stem cells. They are classified according to three different methods:

  • Classification by cell type
  • Classification by ontogenetic age
  • Classification by differentiation potential

 

Classification by cell type

The stem cells can be classified according to which cell types or tissue they are precursors for. A blood stem cell e.g. cannot become new bone or a nerve cell.

 

Hematopoietic stem cells

Another word for hematopoietic stem cells is blood stem cells. These stem cells are responsible for the whole hematopoiesis but have a very limited life span. Every day, about 200 billion of erythrocytes (red blood cells), 120 billion of leucocytes (white blood cells), and 150 billion of thrombocytes (platelets) must be formed in an adult person.

 

Mesenchymal stem cells

Mesenchymal stem cells are the precursor cells of connective tissue. They develop into bone and cartilage as well as muscles, tendons, and ligaments. They are found particularly in the gel-like part of the umbilical cord tissue – Wharton’s Jelly.

stem-cells-types-tasks-fat-tissue-mesenchymal

Human fat tissue is rich in both mature fat cells and in adult mesenchymal stem cells and is therefore a valuable source of stem cells.

 

Neuronal stem cells

Neuronal stem cells are destined to become nerve cells, in particular brain cells. They are especially interesting in the research of neurodegenerative diseases like dementia or Parkinson’s, but also traumatic injuries, e.g. after strokes or serious head injuries caused by accidents. The expectation for the future is that neuronal stem cells may trigger repair processes and thus minimize damages.

 

Classification by ontogenetic age

In biology Ontogenesis is the development of the individual – from the egg cell to the sexually mature organism. The classification by ontogenetic age therefore differentiates between embryonic, fetal, and adult stem cells.

stem-cells-types-tasks-ontogenesis

Embryonic stem cells exist only during the early cell division after fertilization. Adult stem cells divide throughout life.

 

Embryonic stem cells

Embryonic stem cells act in the beginning of human life – long before birth. They are the “mothers of all cells” and can develop into any type of specific cell. However, they exist only for a very short time – namely during the development into the blastocyst, the state of the embryo about three to four days after fertilization. For medical purposes, this means that you would have to grow embryos and destroy them afterwards. Embryonic stem cells are therefore highly controversial from an ethical point of view, and their production is prohibited in the EU.

 

Adult stem cells

Adult stem cells from the bone marrow and other organs are the reservists of our organism. They create substitutions for dead cells. They are no longer able to differentiate into all types of cells in an organism, like embryonic stem cells, and they are not as viable as stem cells from umbilical cord blood. Furthermore, the extraction of adult stem cells is laborious, risky and expensive.

 

Neonatal stem cells

Stem cells from umbilical cord blood technically belong to the adult cells, even though they are particularly young and potent. They are therefore their own class –neonatal stem cells.

 Collecting umbilical cord blood at birth is the most simple and ethically inoffensive way to extract young and potent stem cells; thus securing them for medical precaution for the child.

 

5 great reasons why you should protect your baby's stem cells

  • Stem cells are valuable because they are the body’s building blocks
  • Stem cells are used to treat life-threatening diseases
  • Stem cells shorten critical waiting time
  • Stem cells have a 25% chance of perfect match between siblings
  • Stem cells could revolutionize medical treatment

Classification by differentiation potential

Stem cells can be classified according to how many different cell types they can develop into. All stem cells are not just the same. There is a hierarchy from the generalist to the specialist. The general rule is: The earlier a stem cell develops, the higher is its differentiation potential.

 

Omnipotent/totipotent stem cells

A complete organism can originate from omnipotent or totipotent stem cells. The fertilized egg cell, called the zygote, develops to an embryo by cell division. Omnipotent stem cells exist only in a very short stage of embryonic development: That is until the blastocyst develops three to four days after fertilization, when all organs and tissues are created. The cells arrange themselves in the blastocyst. The outer layers form the so-called trophoblast, which develops into the amniotic sac, the umbilical cord, and the placenta. The inner cell layers form the embryoblast, which becomes the complete human being.

stem-cells-types-tasks-totipotent

When the egg cell and the sperm cell fuse, the zygote develops into the morula through cell division. In humans, this stage of development starts with the 16-cell stage during the embryogenesis . It takes about four days from fertilization to morula. During this time, the stem cells are totipotent, i.e. they can create a completely new organism including placenta, amniotic sac, and umbilical cord.

 

Pluripotent stem cells

Pluripotent stem cells also have the ability to differentiate into all types of cells, but they cannot become an entirely new organism anymore. Pluripotent stem cells are particularly interesting to stem cell research and tissue engineering. The goal of the latter is to grow tissue in a three-dimensional structure and with complex tasks. One day, whole organs could be replaced by means of this method.

 

Multipotent stem cells

Multipotent stem cells can differentiate into various cell types of their specific tissue. E.g. all blood components like erythrocytes, leucocytes, and thrombocytes originate from hematopoietic stem cells. Neuronal stem cells may become different types of brain cells, but can not become muscle cells or heart cells.

 

Oligopotent stem cells

Oligopotent stem cells are still able to differentiate into a few cell types of their tissue. Blood-forming stem cells are multipotent, and when they divide their daughter cells may develop into myeloic stem cells or lymphoid stem cells. Both types of these stem cells are oligopotent only. The myeloic stem cells become erythrocytes, granulocytes, thrombocytes, and monocytes. The lymphoid stem cells become part of the immune system – namely T cells, B cells, and killer cells.

 

Unipotent stem cells

Unipotent stem cells in this hierarchy are those with the lowest differentiation potential. They can only become their own type of cell. An example of unipotent stem cells are spermatogonial stem cells, which are contained in the testicles. They can only become sperm cells.