Stem cells

What is a stem cell?

Stem cells are undifferentiated cells which can keep dividing to give rise to other types of cell types. They can either: 

• Divide by mitosis to produce more stem cells (self-renewal) 

• Differentiate into specialised cells (exits the cell cycle and loses the capacity to divide) 

What are stem cells needed for in the body?

1. Growth 

2. Repair of tissues  

3. Replacement of dead cells  

Totipotent stem cells

• Can differentiate into all types of specialised cells in the body; have the capacity to form an entire organism. In animals, only stem cells from the very early embryo (less than 3 days old) are totipotent

• ‘toti’ = ‘total’, all types of cell

Pluripotent stem cells

• Can differentiate into all types of cell but not a whole organism. Embryonic stem cells from blastocyst stage embryos (3-5 days old; approx. 150 cells stage) are pluripotent. Pluripotent stem cells in mammals can’t form the placenta

Multipotent stem cells

• Can differentiate into multiple types of specialised cells, but not all types. Tissue stem cells are multipotent 

• Bone marrow stem cells can only differentiate into blood cells

Unipotent stem cells

• Stem cells that can only become one type of cell, happens at the end of specialisation 

• An example of unipotent stem cells are cardiomyocytes, heart muscle cells

iPS

• Induced pluripotent stem cells (don’t exist naturally as pluripotent) 

• Adult somatic cells were de-differentiated/reprogrammed them, so that the cells regain the capacity to differentiate into any type of cell in the body 

• No ethical issues (an adult that can give consent), will also be recognised as self-cells and not induce an immune response