Stem Cells and Medical Applications for the ESAT

Introduction to Stem Cells

Stem cells are undifferentiated cells that possess two unique properties. First, they can renew themselves by dividing through mitosis. Second, they can undergo a process called differentiation to specialise into a variety of different cell types. In humans, different types of stem cells are produced at various stages of development, from the earliest moments of life through to adulthood.

Human Development and Stem Cell Types

Humans reproduce via sexual reproduction, where specialised cells called gametes (sperm and egg) fuse during fertilisation to produce a single fertilised egg cell known as a zygote.

The zygote begins to divide by mitosis to produce daughter cells. The cells produced in this very early stage of life are defined as totipotent stem cells. Totipotent cells have the highest level of potency: they have the potential to differentiate into any of the specialised cells found in an adult human and can develop into a complete multicellular organism, including the placenta.

As the number of cells increases, an embryo forms. The embryo consists of pluripotent embryonic stem cells. These cells can still differentiate into any of the specialised cell types of the adult body. However, unlike totipotent cells, pluripotent cells cannot produce the cells required to form the placenta.

Adult humans also possess stem cells throughout their lives. These adult stem cells are found in various organs, including the skin, heart, brain, and liver. Adult stem cells are described as multipotent. They are undifferentiated but can only differentiate into a limited, small number of different cell types. For instance, stem cells in the bone marrow are multipotent and can only differentiate into the various types of cells found in human blood.

In summary, while all stem cells can divide by mitosis and differentiate, the range of potential cell types they can produce decreases as the organism develops from a zygote to an embryo and finally to an adult.

Stem Cells in Medical Applications

Stem cells are already used in medicine. Bone marrow transplants are a established treatment for certain cancers, where the donor's multipotent stem cells replace the patient's diseased blood cells. However, there is significant research into the use of embryonic stem cells to treat conditions where body cells are destroyed or non-functional. By stimulating these cells to differentiate into specific tissues in a laboratory, they could be used for:

1. Treating diabetes by replacing insulin-secreting cells in the pancreas.
2. Treating severe burns by replacing damaged skin tissue.
3. Replacing neurones damaged by spinal cord injuries to treat paralysis.
4. Replacing heart cells damaged during a heart attack.

Risks and Ethical Considerations

The use of stem cells in medicine is not without challenges. Key risks include:

• Immune Rejection: The patient's immune system may identify transplanted stem cells as foreign and attack them.
• Cancer Risk: There is an increased risk that transplanted stem cells may divide uncontrollably, leading to the development of tumours.
• Ethical Concerns: The use of embryonic stem cells is controversial because the process requires the destruction of human embryos, which many people object to on moral and ethical grounds.

Induced Pluripotent Stem Cells (iPSC)

To address the ethical and rejection issues, scientists developed induced pluripotent stem cells (iPSC). These are created in the laboratory by reprogramming adult body cells to behave like pluripotent embryonic stem cells.

The benefits of iPSC include avoiding the use of human embryos and reducing the risk of rejection, as the cells can be produced from the patient's own body. They are also vital for research: scientists can culture cells from a patient to study diseases like Alzheimer's or test the effectiveness of new drugs in cell cultures before they are administered to patients.