stem cells

• a stem cell is an unspecialised cell
• stem cells can proliferate into more stem cells through mitosis or differentiate into a specialised cell
• differentiation is the process by which cells become specialised. during mitosis, different genes become activated, allowing cells to specialise
• stem cells can differentiate under right conditions and are triggered by :

  • internal signals are controlled by genes being on or off
  • external signals are signals in the cells environment like chemicals secreted by other cells, physical contact with other cells and certain molecules in the microenvironment
• potency is the number of possible fates open to a cell, this decreases with age
• totipotent cells have the ability to create any cell of the body and embryonic membrane

  e.g. cells of embryo within the first few mitotic divisions
• pluripotent cells can form any cell of the body but not the embryonic membrane

  e.g. embryonic stem cells
• multipotent cells can only form some cells of the body

  e.g. umbilical cord blood and placental stem cells, adult stem cells