Hematopoietic stem cell differ from progenitor stem cell in that they can –

There are two major types of stem cells 1) Embryonic stem cells (ES) These are pluripotent cells which can differentiate into all the tissues of the human body. 2) Adult stem cells Adult stem cells have a more restricted differentiation capacity and are usually lineage-specific, i.e. multipotent or unipotent. There are two types of adult stem cells A) Bone marrow stem cells These are hematopoietic stem cells which reside in bone marrow and differentiate into various blood cells. Although residing mainly in the marrow, a subset circulates normally in the peripheral blood. From 3 weeks to 3 months of intraembryonic life, hematopoietic stem cells in the yolk sac are the primary source of blood cells. From 3 months to just before birth stem cells, migrate to the liver, which is the major organ for hematopoiesis during that period. After birth bone marrow becomes the major source. A remarkable observation about hematopoietic stem cells is that they may capable of giving rise to neurons, hepatocytes, myocardium, bile duct cells, endothelial cells and skeletal muscle. This change in stem cell differentiation from one cell type to another is called transdifferentiation. Other types of bone marrow stem cells are bone marrow stromal cells which can differentiate, depending on the tissue environment, into chondrocytes, osteoblasts, adipocytes, myoblasts, endothelial cell precursors. B) Tissue stem cells These are located outside the marrow in sites called niche. These include