What are Blood Stem Cells – Definition & Originate

Presentation notes of Blood Stem Cells origin in Bone Marrow, Functions & Lifespan in word/ .pdf/.ppt

STEM CELLS

The stem cells are the primitive cells in the bone marrow, which give rise to the blood cells. As the stem cells can give rise to different types of blood cells, these are called pluripotent hemopoietic stem cells (PHSC) .

In the earlier stages, the stem cells are not designed to form a particular type of blood cell. And it is also not possible to determine the blood cell to be developed from these stem cells. So at this stage, the cells are called uncommitted pluripotent hemopoietic stem cells (Uncom­mitted PHSC).

When the cells are designed to form a particular type of blood cell, the stem cells are called committed pluri­potent hemopoietic stem cells (Committed PHSC). The committed stem cells are of two types namely:

1.  Lymphoid stem cells (LSC) which give rise to lympho­cytes.

2.  Colony forming blastocytes, which give rise to the blood cells other than lymphocytes. When grown in cultures, these cells form colonies hence the name colony forming blastocytes. There are different units of colony forming cells as follows:

  • Colony Forming Unit—Erythrocytes (CFU-E). The stem cells of this unit develop into erythrocytes.
  • Colony Forming Unit—Granulocytes/Monocytes (CFU-GM). These cells give rise to granulocytes (neutrophils, basophils and eosinophils) or Mono-cytes.
  • Colony Forming Unit—Megakaryocytes (CFU-M). From these, platelets are developed.

CHANGES DURING ERYTHROPOIESIS

The stem cells of the colony forming unit—E (CFU-E) pass through different stages and finally become the matured red blood cells. During this process four important changes are noticed.

1.   Reduction in size of the cell (from the diameter of 25 m to 7.2 m)
2.   Disappearance of nucleoli and nucleus
3.   Appearance of hemoglobin and
4.   Change in the staining properties of the cytoplasm

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