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Stem cells in humans

An embryo develops from a fertilised egg. Cells in the early stages of the development of an embryo are known as . These are cells that have not undergone . A cell which has not yet become is undifferentiated.

If cells are removed from the embryo they will differentiate into any cell type. These are called embryonic stem cells. Some stem cells remain in the bodies of adults as adult stem cells.

Adult stem cells can be found in limited numbers in several regions of the body, eg:

Adult stem cells can differentiate into related cell types only, for instance, bone marrow cells can differentiate into blood cells and cells of the immune system, but not other cell types.

Using human stem cells

Stem cells can divide to produce new cells, which can then divide into different cell types. They therefore have the potential to be transplanted into patients to treat medical conditions and disease. They could be used to replace cells that have been damaged or destroyed, for example:

in type 1 diabetes

in cases of multiple sclerosis, which can lead to paralysis

in cases of spinal cord or brain injury, which have led to paralysis

The stem cells used could be:

Embryonic stem cells can differentiate into a wider range of cell types, but are difficult to obtain. The best source is the five-day-old embryo.

Adult stem cells will differentiate into a narrower range of cell types. Bone marrow transplants are an example of adult stem cell transplant. Bone marrow cells will differentiate into different types of blood cells. Bone marrow transplants are carried out:

when blood cells have been destroyed, eg during cancer treatment

Benefits and risks associated with the use of stem cells in medicine

Stem cells have great potential, eg in treating patients with currently untreatable conditions, growing organs for transplants, and research. The benefits of using your own stem cells include:

But there are clinical, and social issues associated with their use. These issues will be different for the growth and transplant of adult, embryonic, or therapeutically-cloned stem cells. They will also depend on whether the stem cells are to be used for therapy or research.

Clinical issues

There is no guarantee how successful these therapies will be, for example, the use of stem cells in replacing nerve cells lost in Parkinson's disease patients.

The current difficulty in finding suitable stem cell donors.

The difficulty in obtaining and storing a patient's embryonic stem cells. These would have to be collected before birth - some clinics offer to store blood from the umbilical cord when a person is born.

Mutations have been observed in stem cells cultured for a number of generations, and some mutated stem cells have been observed to behave like cancer cells.

Cultured stem cells could be contaminated with viruses which would be transferred to a patient.

Ethical issues

One source of embryonic stem cells is unused embryos produced by in vitro fertilisation (IVF).

For , is it right to create embryos for therapy, and destroy them in the process?

Embryos could come to be viewed as a commodity, and not as an embryo that could develop into a person.

At what stage of its development should an embryo be regarded as, and treated as, a person?

Social issues

Educating the public about what stem cells can and cannot do is important.

Whether the benefits of stem cell use outweigh the risks.

Much of the research is being carried out by commercial clinics, so reported successes are not subject to peer review.

Patients could be exploited by paying for expensive treatments and being given false hope of a cure as stem cell therapies are only in their developmental stages.

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BBC Bitesize - GCSE Biology (Single Science) - Cell division and stem cells - WJEC - Revision 3

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An embryo develops from a fertilised egg. Cells in the early stages of the development of an embryo are known as . These are cells that have not undergone . A cell which has not yet become is undifferentiated. If cells are removed from the embryo they will differentiate into any cell type.

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Therapeutic cloning - The production of embryonic stem cells for use in replacing or repairing damaged tissues or organs, achieved by transferring a diploid nucleus from a body cell into an egg whose nucleus has been removed.

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What Are Stem Cells | Biology for All | FuseSchool

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GCSE Science Revision Biology "Stem Cells"

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During the development of an embryo embryo: The developing human offspring inside the womb most of the cells become specialised. They cannot later change to become a different type of cell.

But embryos contain a special type of cell called stem cells. These can grow into any type of cell found in the body. They are not specialised. Stem cells can be removed from human embryos that are a few days old, for example, from unused embryos left over from fertility treatment.

Watch

You may wish to view this BBC News item (2007) about a British research team that grew human heart valves from stem cells for the first time.

Here are some of the things stem cells could be used for:

Making new brain cells to treat people with Parkinson's disease

Rebuilding bones and cartilage

Repairing damaged immune systems

Making replacement heart valves

Therapeutic cloning

If you were to receive medical treatment with cells grown from stem cells, your body's immune system would recognise the cells as foreign, and they would be rejected and die. But this would not happen if you received cells with the same genes as you.

This could be done by cloning one of your cells to produce an embryo, then taking stem cells from this. This is called therapeutic cloning. Here are the steps involved:

Nucleus [ nucleus: The central part of an atom. It contains protons and neutrons, and has most of the mass of the atom. ] taken out of a human egg cell

Nucleus from a patient's cell put into the egg cell

Egg cell stimulated to develop into an embryo

Stem cells taken from the embryo

Stem cells grown in a container of warm nutrients

Stem cells treated to develop into required cell types

Ideas about science - weighing up arguments

The cloning of human embryos is controversial. You need to use your ideas about science to explain the argument. Remember to:

Say clearly what the issues are. For example, some human embryos will be destroyed during the cloning process.

Summarise different views that might be held. For instance, some people think that this is murder. Others believe it is furthering our knowledge of science for the benefit of everyone.

Identify and develop arguments based on the idea that the right decision is the one that has the best outcome for the majority of people. For example, even though a few embryos will be destroyed, many people will be free from suffering and cured of diseases that are currently incurable

Identify and develop arguments based on the idea that certain actions are very hard to justify because they are considered unnatural and wrong. For example, some people think that, no matter what the benefits are of curing a disease, we should not clone embryos because destroying human life is always wrong.

Take care not to confuse adult and embryo stem cells - adult stem cells will only differentiate into a few types of cells. Adult stem cell research tends to be less controversial.

Remember that these types of decisions are values, and produce questions that cannot be answered by science.

Now try a Test Bite.

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During the development of an embryo embryo: The developing human offspring inside the womb most of the cells become specialised. They cannot later change to become a different type of cell. But embryos contain a special type of cell called stem cells. These can grow into any type of cell found in the body.