Download Stem cells powepoint File

Stem Cells
Where we find them, and how they can
be used in medicine.
Specification
• 11 Explain what is meant by the terms stem cell, pluripotency
and totipotency and discuss the way society uses scientific
knowledge to make decisions about the use of stem cells in
medical therapies (e.g. regulatory authorities relating to
human embryo research, ability of stem cells to develop into
specialised tissues, potential sources of stem cells, who could
benefit from the therapies, procedures to obtain stem cells
and their risks).
• 12 Describe how totipotency can be demonstrated practically
using plant tissue culture techniques.
What is a stem cell?
A stem cell is a cell that is able to replicate itself indefinitely by
mitosis while maintaining an undifferentiated state, and is then
able to differentiate into mature cell types.
What are the three basic types of stem cells in humans?
How are they different?
http://www.sumanasinc.com/webcontent/animations/content/
stemcells.html
As you watch- What two properties do pluripotent embryonic
stem cells have?
Read p120-121 and fill in 3.12a Stem Cells Table
Activity 3.12a Stem Cells
Type of
stem cell
totipotent
pluripotent
Definition
are undifferentiated cells which can
divide indefinitely by mitosis and
differentiate into all the cell types in
an organism.
Source of stem cell
They are the first eight cells in an
embryo.
Are undifferentiated cells which can
They are the inner mass (50 cells)
divide indefinitely by mitosis and
of the blastocyst stage of an
differentiate into most, but not all cell embryo.
types in an organism (not into
totipotent cells or into extraembryonic cells).
are differentiated cells which retain
multipotent the ability to divide indefinitely by
mitosis and differentiate into a
limited amount of different cell types.
In adults , for example, cells in the
bone marrow can give rise to
range of different types of blood
cells (white and red).
Use of Stem Cells in Medicine and Research
• Read pages 122
• Which stem cells are used the most in medicine and how?
• Pluripotent (embryonic), Provide universal new donor
cells, tissues or organs for treatment by transplantation.
• What are the problems that must be overcome when cells,
tissues or organs are transplanted?
•Risk of infection from donor or from equipment (always
possible for invasive surgery)
•If the right type of tissue is developed, there may still be
issues with rejection by the body’s immune system.
• How can we prevent the recipient’s immune system rejection
of universal tissues and organs created from stem cells? Read
p 122-123
• Complete Activity 3.12b Stem Cell table (see next slide)
Who would benefit from embryonic stem cells? Give specific
examples
• Parkinson’s disease: Replace faulty brain cells
• Diabetes: Replace insulin producing tissue in the pancreas
• Damaged nerves: Replace spinal nerves so that limbs can work
again.
• Heart damage from a heart attack: Repair damage with new
heart muscle
• Organs for transplant: Replace organs that no longer work,
such as livers, kidneys, hearts etc.
Therapeutic Cloning
You can now add notes to the diagram in Your handout
Ovum has haploid nucleus removed
Diploid nucleus is
removed from patient
needing transplant
This cell is then stimulated to
divide by mitosis. After 5 days
there should be a blastocyst
Diploid nucleus fused
with ovum using
electric shock
(somatic cell nuclear
transfer)
Stem cells are then isolated
from blastocyst and used to
create tissues that are
genetically identical to
patient
http://www.barglow.com/cloning-1.gif
Or? Therapeutic Cloning
http://www.wwnorton.com/college/biology/discoverbio3/core/cont
ent/ch15/animations.asp 15.4: Human Cloning
How can we prevent the recipient’s immune system rejection of universal tissues and organs
created from stem cells lines?
Tissue
typing
Use of
Drugs
Reduces the chances of rejection but does not
guarantee it
immunosuppresant drugs to reduce rejectionBut this leads to increased risk of infection.
Therapeutic Embryos are developed with recipient’s own DNA. Pluripotent
stem cells from blastocyst are encouraged to develop into
cloning
needed cell, tissues and organs
No rejection at all.
QUESTIONS for a Quiz
1. What is a stem cell?
(3)
2. Where can pluripotent cells be obtained from? (1)
3. Give an example of where multipotent cells can be obtained from.
(1)
4. What type of stem cell is (partly) differentiated and can only
become a few other cell types?
(1)
5. How do totipotent stem cells differ from other stem cells?
(1)
6. Which type of stem cell can become most of the cell types in an
organism?
(1)
7. Give one way in which stem cells can be used in medicine?(1)
Answer for quiz
1. A stem cell is a cell that is has the unlimited ability to
replicate itself by mitosis; undifferentiated state; and is then
able to differentiate into other cell types.
2. Inner cell mass of a blastocyst
3. Bone marrow
4. Multipotent
5. They can differentiate into all cell types
6. Pluripotent
1. Provide universal new donor cells, tissues or organs for
treatment by transplantation.
• Therapeutic cloning has been allowed by
the government, but all embryos must be
destroyed after 14 days, to avoid human
cloning.
Type of cell
How obtained or how
produced
Pluripotent
human stem
cells
Therapeutic
cloning
(somatic cell
nuclear
transfer)
(Human and
animalhuman)
Mutipotent
adult stem
cells
Isolated from ‘spare
embryos’ from IVF
treatment
(50 inner cells removed
from blastocyst)
•
•
•
•
Remove patient’s diploid cell
nucleus
Insert into ovum which has
previously had its nucleus
removed
Mitosis happens and a
blastocyst forms
50 inner cells removed to
produce tissues that are
genetically identical to patient
Neural stem cells from CNS.
Blood stem cells from bone
marrow.
Potential medical
benefits
Legal or ethical issues
Used in research
Used to develop
tissues/organs for
transplantation
Problem: Immune sytem
rejection
• Drugs to suppress
immune system
• Use tissue typing to
match to patient’s tissue
Legal to use surplus
embryos form IVF
treatment
Ethical issues: see
handout.
No rejection by the
immune system
because tissues are
genetically identical
Legal for therapy
only
Ethical issues: see
handout (not all
arguments can be
used)
Less valuable for research
No ethical
because differentiated
Transplantation- no rejection if considerations.
donor and recipient are the same
Ethical Considerations of using Embryonic Stem Cells
AGAINST:
• Embryonic stem cells are (potential) people/babies from the moment of conception
(Objectional on religious grounds)
• Pressure on women to produce surplus embryos
• Cloning/stem cell techniques may get into the wrong hands/regulation might be
difficult to police
• It will soon be possible to use non-embryonic stem cells so research into the use of
embryonic stein cells is unnecessary
• Although there are some advantages there could be unexpected dangerous
consequences therefore not worth the risk
FOR:
• Potential for alleviating human suffering e.g. culturing patient’s own cells to provide
replacement tissues/organs
• Stem cells from IVF would otherwise be discarded;
• Embryos should not be considered as human at an early stage (from blastocyst stage)
• More can be done with embryonic stem cells than differentiated adult stem cells;
• Ethically questionable to use embryonic stem cells but these objections are
outweighed by the greater evil of not using embryonic stem cells to alleviate human
suffering
• Could be excesses but these can be regulated
Plants and Stem Cells
• Do plants have stem cells?
• Yes, actually most plant cells remain totipotent
throughout the life of a plant
• Plant cells can dedifferentiate e.g. a root hair cell can
change into a palisade cell exposed to the correct
chemical signals. Therefore you can grow a whole new
plant from a root, stem, leaf.
• Plants can be reproduced by using plant tissue culture
(micropropagation)
Plants and Plant Tissue Culture (Micropropagation)
• Micropropagation producing many plants which are genetically
identical (clones)
• Put the following steps in order
a) The callus grows into an embryonic plant
b) Place explants on a solid agar medium which will contain
nutrients and growth regulators
c) Surface sterilise the explants to remove bacteria and fungi,
and thus avoid the plant growing poorly or death
d) Embryos form into genetically identical clones
e) Remove small pieces of plant to be cloned – these are called
explants
f) The cells divide by mitosis to form a mass of undifferentiated
cells known as a callus
Answer: 1)e, 2)c, 3)b, 4)f, 5)a, 6)d
• Why is plant tissue culture important?
•
•
•
•
Plant biology research
Plant breeding
Genetic modification of plants
Conservation of endangered plants
• Activity 3.11 Plant tissue culture
• Homework – Stem Cell Exam Questions – Can not yet
answer 2 a (ii) or 3 c
Regulatory Authorities
• Read page 124
• What are regulatory authorities?
• What are their roles?
NOT USED
More information on obtaining stem cells
• Pluripotent Stem cells:
• Spare embryos created during IVF: Those that aren’t
implanted can have stem cells removed from the inner
blastocyst.
• Umbilical cord blood: Contains pluripotent cells that can be
cultured.
• Adult stem cells:
• Found in the brain, liver, skin, bone marrow etc. There are
very few and they can be difficult to harvest, but some are
already used to treat cancers.
Now read p123 Ethical concerns about the use of stem cells and complete the last
column of Activity 3.12b Potential Medical Use of Stem Cells
Read page 124.
What is the role (are the roles) of regulatory bodies?
Type of
Stem Cell
Source of the
Stem Cells
Stem Cell
Potential
Use in
Medicine
Ethical
Considerations
Embryonic Totipotent
After zygote has
gone through 3
cycles of
division, it
consists of 8
identical cells.
Each cell can
develop into a
complete human
being.
Do not
reproduce after
8 cells. Can not
be kept in lab as
cell culture.
Not used often.
Embryonic Pluripotent
Inner cell mass
of the blastocyst
(50 cells that
would usually
form embryo).
Spare embryos
from in vitro
fertilsation
clinics.
Can develop intp
most cell types
but not an entire
human being.
Develop tissues
for
transplantation.
(Possible IS
rejection)
See table on
next page.
Adult –
Mulitpotent
Neural stem cells
from CNS. Blood
stem cells from
bone marrow.
Cells have become
differentiated.
Neural stem cells
become different
neurones
Limited. Less
valuable for
reaserch
because
differentiated.
No ethical
considerations.