Global challenges Study Guide

Stem cells are undifferentiated cells that have the remarkable ability to develop into many different cell types. They can also divide to produce more stem cells. This unique property makes them incredibly valuable for medical research and treatments. There are several types of stem cells, including embryonic stem cells (derived from embryos) and adult stem cells (found in mature tissues like bone marrow).

The potential benefits of stem cell use in medicine are vast. They offer hope for treating many debilitating diseases and injuries where existing therapies are limited. For example, stem cells could be used to replace damaged tissues or organs, such as in spinal cord injuries, Parkinson's disease, or heart disease. They could also be used to grow new organs for transplantation, reducing reliance on organ donation and the risk of immune rejection. Furthermore, stem cells are invaluable tools for studying disease mechanisms and for testing new drugs, providing a more accurate model than animal testing.

However, the use of stem cells, especially embryonic stem cells, presents significant ethical and practical challenges. One major risk is the potential for uncontrolled cell growth, leading to tumour formation if the cells are not properly controlled after implantation. There is also a risk of immune rejection if the transplanted stem cells are not genetically matched to the patient, although adult stem cells from the patient themselves can mitigate this. Ethical concerns primarily revolve around the destruction of embryos to harvest embryonic stem cells, which some people consider to be the destruction of potential human life. There are also practical issues like the difficulty in culturing stem cells, ensuring their purity, and the high cost of treatments. These factors necessitate careful consideration and a balanced approach when evaluating stem cell therapies.

The human immune system is a complex network of cells, tissues, and organs that work together to protect the body from harmful invaders, such as bacteria, viruses, fungi, and parasites, which are collectively known as pathogens. This system is crucial for maintaining health and preventing disease. It functions by identifying and destroying these foreign substances while distinguishing them from the body's own healthy cells. The immune system operates in several layers of defense. The first line of defense includes physical barriers like skin and mucous membranes, which prevent pathogens from entering the body. Chemical barriers like stomach acid and tears also contribute to this initial protection. If these barriers are breached, the innate immune system provides a rapid, non-specific response. This involves white blood cells, such as phagocytes (e.g., neutrophils and macrophages), which engulf and destroy invading microorganisms. The inflammatory response, characterised by redness, swelling, heat, and pain, is also part of the innate immune system, designed to isolate the infected area and bring immune cells to the site. The adaptive (or specific) immune system provides a more targeted and long-lasting defense. It recognises specific pathogens and produces antibodies and specialised cells, such as lymphocytes (B-cells and T-cells), which can remember past infections. This 'memory' allows the immune system to respond more quickly and effectively to subsequent exposures to the same pathogen, leading to immunity.