Stem Cells

• Stem cell


  A cell that can divide (by mitosis) an unlimited number of times
• Stem cell


  • Each new cell (produced when a stem cell divides) has the potential to remain a stem cell or to develop into a specialised cell such as a blood cell or a muscle cell (by a process known as differentiation)
• Potency


  The ability of stem cells to differentiate into more specialised cell types
• Types of potency


  • Totipotency
  • Pluripotency
  • Multipotency
• Totipotent stem cells


  Stem cells that can differentiate into any cell type found in an embryo, as well as extra-embryonic cells (the cells that make up the placenta)
• Pluripotent stem cells


  Embryonic stem cells that can differentiate into any cell type found in an embryo but are not able to differentiate into extra-embryonic cells (the cells that make up the placenta)
• Multipotent stem cells


  Adult stem cells that have lost some of the potency associated with embryonic stem cells and are no longer pluripotent
• As tissues, organs and organ systems develop, cells become more and more specialised
• Having differentiated and specialised to fulfil particular roles, most adult cells gradually lose the ability to divide until, eventually, they are no longer able to divide
• Adult stem cells


  • Small numbers remain to produce new cells for the essential processes of growth, cell replacement and tissue repair
  • Although these adult stem cells can divide (by mitosis) an unlimited number of times, they are only able to produce a limited range of cell types - they are multipotent
• Multipotent adult stem cells

  • Stem cells found in bone marrow - they can only differentiate into blood cells (red blood cells, monocytes, neutrophils and lymphocytes)
• In adults, multipotent stem cells can be found throughout the body (eg. in the bone marrow, skin, gut, heart and brain)
• Stem cell therapy


  The introduction of adult stem cells into damaged tissue to treat diseases (eg. leukemia) and injuries (eg. skin burns)
• Stem cells can be totipotent, pluripotent or multipotent
• Stem cell types


  • Totipotent
  • Pluripotent
  • Multipotent