8.2.2 Stem Cells

What are Stem Cells?

• Stem cells are undifferentiated cells capable of:
  • Self-renewal: Continuously dividing to produce more stem cells.
  • Differentiation: Giving rise to specialised cell types.

Types of Stem Cells

1. Totipotent Stem Cells:

• Found in the early embryo.
• Can differentiate into any type of specialised cell, including extra-embryonic cells (e.g., placenta).

2. Pluripotent Stem Cells:

• Found in the later stages of the embryo.
• Can differentiate into many types of specialised cells, but not extra-embryonic cells.

3. Multipotent Stem Cells:

• Found in adult tissues (e.g., bone marrow).
• Can differentiate into a limited range of cell types.
• Example: Haematopoietic stem cells give rise to different blood cells.

4. Unipotent Stem Cells:

• Found in specific tissues.
• Can differentiate into only one type of cell.
• Example: Skin stem cells that produce new skin cells.

Key Features of Stem Cells

• Stem cells play a critical role in:
  • Growth.
  • Repair of tissues.
  • Replacement of damaged or dead cells.
• Stem cells' ability to differentiate is due to selective gene expression.

Stem Cells in Medicine

• Stem cells are used in regenerative medicine:
  • Treating diseases such as leukaemia (using bone marrow transplants).
  • Potential for use in repairing damaged tissues, e.g., in spinal cord injuries.

Ethical Considerations

• Embryonic stem cells: Using embryos to obtain pluripotent stem cells raises ethical concerns about the destruction of embryos.
• Adult stem cells: An alternative that avoids ethical issues but has a limited range of differentiation compared to embryonic stem cells.