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  • STEM CELLS

  • We hear a lot about stem cells these days,

  • but what are they, where do they come from

  • and what do we really know about them?

  • Inside our bodies there's a microscopic world,

  • busy and complex like the world around us.

  • Stem cells build and maintain this world.

  • This is a story of stem cells and their lives

  • inside and outside our bodies.

  • Life begins with one cell, the fertilised egg.

  • Throughout development cells divide over and over again

  • to produce the billions of cells that make up the body.

  • At certain stages, most cells stop making copies of themselves

  • and start to specialise.

  • When we are fully formed almost all our cells are specialised.

  • Cells are beautiful things when you see them down a microscope.

  • Normally they're so miniscule we can't see them,

  • even though they're what make us.

  • And each type of cell has its own characteristic.

  • Some types of cell grow very closely together

  • and form beautiful patterns.

  • Other types of cell will move away from one and other.

  • Some cells become big, others are always very small.

  • It depends on what type of cell they are.

  • These different cell types work in specialised teams.

  • Some carry oxygen through the blood system,

  • some do the stretching and contracting in our muscles,

  • some carry messages between our brain and the rest of our body.

  • Stem cells are very special cells They act as a resevoir,

  • because the specialised cells

  • can no longer make copies of themselves.

  • So, if they die and get used up, they have to be replaced from somewhere.

  • And this is where the stem cells function.

  • Stem cells are used in the blood system.

  • We need to make millions of new blood cells every day

  • and these are generated from stem cells.

  • And these cells actually live in the bone marrow.

  • Altogether a blood stem cell can make eight different types

  • of specialised cell.

  • They're used in the skin.

  • We need to make new skin cells all the time

  • because we're always wearing away our skin.

  • And actually now we know they're present even in the brain.

  • We always have to make new stem cells,

  • so they're not completely exhausted,

  • because otherwise we'd lose the capacity to make any new cells.

  • So the stem cell has to make a decision.

  • Every time it divides, it produces two daughter cells,

  • and those daughter cells can be new stem cells,

  • or they can be specialised cells.

  • Stem cells in the adult tissues can normally only make

  • the type of cell in that tissue.

  • So a stem cell in the skin, can make cells in the skin,

  • but it can't make blood cells and vice versa.

  • Stem cells are already useful in medicine.

  • One skin stem cell alone can produce enough specialised skin stells

  • to cover the whole body.

  • This produced a breakthrough in the treatment of extensive burns.

  • 1ST DEGREE BURN...

  • When a person is heavily burnt, we take a sample

  • from an unburnt area and we take apart the skin sample

  • and we get the cells out of it,

  • and we seed the cells in a culture flask like this one.

  • We feed the cells with a special liquid, which is full of protein and sugar.

  • They need to eat like you.

  • At some point, these cells will divide, will multiply.

  • And they will cover the entire bottom of the flask.

  • We remove the cells using a special chemical

  • and we take this sheet of cells into the surgery room

  • and transplant the patient with it.

  • We can do only part of the skin today,

  • which means we can do the outer most layer of the skin,

  • which is very important, because without this layer you wouldn't be able to survive.

  • However, we cannot reconstruct sweat glands our hair follicles.

  • So these burnt patients have had their lives saved by stem cells,

  • but they have no hair and they don't sweat.

  • That is obviously a problem.

  • They are alive, but I can't say they have a normal life.

  • That's why many laboratories are trying to understand

  • how the skin is built to be able to reconstruct it in the lab,

  • so we can improve the life of these patients.

  • Stem cells are also used to treat patients with blood disorders,

  • such as leukaemia.

  • A transplant of just a few blood stem cells,

  • is enough to repair the entire blood system.

  • Stem cells for specific tissues and organs

  • can only make the cells of that tissue.

  • We know there are stem cells in skin, blood, guts and muscles,

  • but we don't know whether other organs have their own stem cells,

  • or how useful they will be.

  • Back along the chain of development, there's another kind of stem cell.

  • It's controversial. It can become any specialised cell.

  • The embryonic stem cell.

  • This cell comes from a blastocyst, the stage of development

  • before implantation in the uterus.

  • For fertility treatment, blastocysts are produced in the laboratory.

  • If they are not used for a pregnancy, they can be donated for research.

  • In the early embryo, there's a group of cells

  • that can give rise to all the tissues of the body.

  • These are the cells we're very interested in

  • because we know that we can take the cells from the early embryo

  • and grow them in culture, and maintain them in a state

  • where they can contribute to all the tissues.

  • What we're seeing here is the blastocyst stage of development.

  • It's smaller than a pin head.

  • You can't see it without the microscope.

  • So at this stage, the cells in the embryo - these are the cells -

  • they can make any tissue at all.

  • What we have to do, is isolate these cells.

  • One way is we can remove the trophectoderm cells

  • so that we're just left with a clean inner cell mass.

  • So we can grow these in culture, and they'll multiply

  • until we have lots of these cells

  • that still have the capacity to form

  • any tissue at all.

  • Embryonic stem cells can become heart, blood, brain or skin cells

  • depending on the way they are grown.

  • These stem cells have turned into heart cells.

  • When you're working with stem cells, you're always observing the cells

  • and you're trying to understand how it is they can do what they can do.

  • You're trying, actually, to make them do what you want to do.

  • It's almost like a battle of wills.

  • A stem cell goes through a long series

  • of decisions to become a specialised cell.

  • A combination of internal and external signals guide each stem cell

  • along the path towards specialisation.

  • These signals are normally provided by the body.

  • By figuring out how to recreate these signals in the lab,

  • scientists aim to grow pure populations of almost any cell type.

  • The challenge to us is to understand each decision and how it's controlled.

  • And then how to provide those signals,

  • to impose the direction on the sytem.

  • And once we get to a point where that begins to happen,

  • then you suddenly see that you could use it

  • to address medical conditions and problems.

  • Work that we have been doing recently

  • has been focussed on trying to make stem cells for the brain

  • from embryonic stem cells. And it turns out we're able to do this.

  • These neural stem cells are now no longer able to make all cells,

  • they can only make three types of cells, the three types that exist in the brain.

  • So this is an important first step in creating a useful and powerful system,

  • that can both be applied for drug screening and perhaps in the end for transplantation.

  • These lab-grown human cells, produced in large numbers,

  • provide improved models for testing new medical treatments

  • and may reduce the need for animal testing.

  • The same cells may help us understand what goes wrong in complex diseases,

  • like Alzheimer's, Parkinson's and diabetes.

  • Diabetes is a chronic disease defined by high blood sugar levels

  • that stay high just because there is not enough insulin.

  • We know that the insulin is produced by cells in the pancreas.

  • We call them beta cells.

  • Transplantations of those cells are now done in clinics.

  • Those cells are isolated from donor organs.

  • After transplantation with those cells, you can normalise diabetes.

  • You can correct diabetes.

  • The major obstacle to beta cell transplantation in diabetes

  • is the shortage of donor cells.

  • We can transplant only 25 patients per year,

  • while there are more than 50,000 patients in Belgium that are treated with insulin.

  • We have to look for other techniques

  • to produce insulin-making cells in the laboratory.

  • What the researchers try to do

  • is first examine this path, this evolution

  • between the embryonic stem cell and the insulin-producing beta cell,

  • and then to also try to isolate the different stages,

  • the different kind of stem cells on the way to beta cells.

  • If one can then isolate them and let them grow in the laboratory

  • then you can make as many insulin-producing cells as you want.

  • And that's the goal of many investigators in the world.

  • The embryonic stem cell area is a very exciting area.

  • It really has opened a new world, that of regenerative medicine.

  • We have now bridges between all the laboratories

  • that have a particular expertise.

  • Working together, we will be in a good position

  • to examine, to investigate its enormous potential,

  • but the enthusiasm should not cover all the technical and scientific

  • questions and obstacles that exist

  • and that will have to be studied very carefully.

  • Stem cell research is a fast-moving field.

  • Around the world, new findings are constantly reported,

  • creating new questions and fresh challenges for scientists

  • seeking to harness these cells and to shape future medicine.

  • So cells are the building blocks of the tissues and organs of the body.

  • And many people are interested in this.

  • What captured my imagination, was when I realised that

  • in development, cells actually have to make choices

  • and decide to become different types of cell,

  • and understanding how that is controlled, how that decision is made...

  • If you could understand that, it seems to me,

  • then you would understand the most important thing about life.

STEM CELLS

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B1 中級 美國腔

一個幹細胞的故事 (A Stem Cell Story)

  • 193 17
    Anastasia Chang 發佈於 2021 年 01 月 14 日
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