Stem Cells and the Blood-Forming System

What are Stem Cells?

  1. Stem cells have 4 characteristics.
  2. Stem cells have the capacity for self-renewal.
  3. Stem cells are undifferentiated.
  4. Stems cells have the greatest proliferation potential of all other cells in the body.
  5. Stem cells have the capability of producing one or more lineages of mature, functional cells. 

The Blood-Forming System 

Hemato- or hemopoiesis literally means "blood production" or "blood-forming".

Hematopoiesis is one of a handful of biological systems that has the capacity for continuously producing cells throughout life.

The blood-forming system is unique in three ways:

  1. It is the only biological system whose tissue production site changes as development proceeds from an embryo to a fetus and finally to an adult.
  2. It is the only biological system in which cells are produced in a specific tissue and are then released to circulate through arteries, veins and capillaries to all parts of the body.
  3. It is the only biological system that produces a variety of different cell types each with a different function, all of which are derived from a single cell, the hematopoietic stem cell.


A healthy person produces about 1 million red blood cells and about 200,000 white blood cells every second of their life.

Besides red blood cells, the erythrocytes, which carry oxygen to all parts of the body, the white blood cells consist of at least 7 different types of cells. These are, neutrophils, basophils and eosinophils, collectively called granulocytes, macrophages, platelets and T- and B- lymphocytes. Their function is to protect and help the body in wound healing and against infection and harmful agents. Thus, together there are 8 primary types of blood cells.

All blood cells are produced from a very small population of "hematopoietic stem cells". A single stem cell is capable of being induced into any one of the different types of blood cells mentioned above.

To become a mature blood-cell, the stem cell has to pass through several rounds of division and simultaneously differentiate from a very primitive cell to one that has developed the functional capabilities it has been determined to possess.

The stem cell undergoes a process of determination into lineage-specific progenitor and precursor cells. These cells form the so-called amplification compartment. The compartment provides the large number of mature cells required by the body. The precursor cells gradually loose their potential for division and differentiate and mature further. Finally, the cells enter a maturation compartment. These four compartments are shown graphically below.

Heirarchy