Stem Cells

• 2 methods of stem cell division are symmetric which produces 2 identical stem cells for self-renewal and asymmetric which produces one differentiated cell and one daughter cell identical to the parent cell. This allows both self-renewal and differentiation/repair.
• Key features of stem cells are their ability to self-renew and differentiate. Stem cells are important in development, cell replacement & repair.
• Stem cells are regulated by their niche, the intrinsic environment and extrinsic environment. Stem cell niches are found on the outside of the ECM with stem cells on the inside of the ECM.
• Extrinsic regulation of stem cells involves neighbouring cells, growth factors/cytokines, and niche & stem cell orientation.
• Intrinsic regulation of stem cells involves growth factor gradients, transcriptional regulators, cell cycle regulators, signal pathways & cell survival. 
• Stem cells can differ based on origin and potential. They can be adult or embryonic, and totipotent, pluripotent, multipotent & unipotent.
• Embryonic stem cells can form the mesoderm, endoderm & ectoderm. Blastocyst inner mass cells are found outside of the embryo proper and can form all cells except those of the extra-embryonic tissues (are pluripotent). 
• Adult stem cells are multipotent or unipotent, and allow tissue repair & maintenance.
• Totipotency occurs up to the 8 cell stage and means cells can differentiate into any embryonic or extraembryonic tissues.
• Pluripotent stem cells are found in the inner cell mass of blastocysts, and form the epiblast layer.
• Multipotent stem cells are found from the morula onwards and can differentiate into all embryonic but not extraembryonic cells.