Stem Cells

Question 1

What is a stem cell?

Answer 1

cells that have not yet specialised.

Question 2

talk through the development of an embryo. Zygote, morula, blastocyst, gastrula, embryo

Answer 2

Start as a single cell, a fertilised egg (zygote).
Morula: when zygote undergoes mitosis. A ball of unspecialised embryonic stem cells.
When morula has 16 cells (3-4 days) it enters the uterus.
Blastocyst (day 5): when cells begin to specialise. Has a single layer of surface of cells that implant in the uterus and develop into placenta and the inner cell mass becomes the embryo.
Gastrulation occurs over five days forming a gastrula.
Gastrula (day 12): three layers of cells.
Becomes an embryo (week 3) an the a foetus (week 8). Recognisable as a human.
Week 5/embryo stage: brain, spinal cord and heart develop, tissues grow into bones, eyes and ears form, limbs buds develop from ectoderm and mesoderm, webbing between fingers and toes is eventually removed by apoptosis.

Question 3

what is gastrulation?

Answer 3

folding into three layers of cells to make a gastrula.

Question 4

what are the germ layers?

Answer 4

ectoderm, mesoderm, endoderm.

Question 5

how are the germ layers supported and sustained?

Answer 5

Layers are supported by membranes: yolk sac which surrounds egg yolk and has a developed system which transports nutrients from the egg yolk to the embryo and the amnion which surrounds the embryo and is filled with fluid. It is a shock absorber.

Question 6

what does each germ layer become?

Answer 6

Ectoderm: outer layer forms epidermis, hair, PNS, brain and spinal cord cells.
Mesoderm: middle layer forms muscle, cartilage, kidney and gonad cells.
Endoderm: inner layer that forms lungs, bladder and lining of digestive system cells.

Question 7

what can stem cells do?

Answer 7

Can replicate into new stem cells.

Can differentiate into cell types.

Question 8

what are embryonic stem cells? where are they gotten? divisions?

Answer 8

Undifferentiated cells of embryos (zygote and blastocyst stage).
Obtained from surplus 3 to 5 day old embryos from IVF.
Replicate indefinitely.

Question 9

what are adults stem cells? where are they found? what are some features?

Answer 9

Present in small amounts in adult tissues such as hair follicles, bone marrow, the spinal cord and germ cells.
Repair and regenerate damaged and aged tissue.
Limited number of cells it can differentiate into.
Cannot replicate indefinitely.

Question 10

what is potency?

Answer 10

A cells ability to differentiate.

The more types it can differentiate into, the more potent.

Question 11

what are the different potencies?

Answer 11

Totipotent: capable of any cell type or even another embryo. Zygotes are the only ones.
Pluripotent: can differentiate into any of the three germ layers. Present in blastocysts. Primordial germ cells that become gametes are pluripotent.
Multipotent: can become multiple types of cells.
Unipotent: differentiate into one type of cell eg. Skin cells.
Embryonic stem cells are totipotent or pluripotent.
Adult stem cells are multipotent or unipotent.

Question 12

how do stem cells get implanted?

Answer 12

Stem cells can be injected to repair damage.

Question 13

what must happen for stem cell therapy to work?

Answer 13

stem cells must be able to replicate in cultures.
Must be able to replicate into the needed cell.
Must not remain as self-renewing cells with the potential to grow out of control.
The immune system must not reject them- embryonic cells are better accepted than adult stem cells unless the adult stem cells are from the person.

Question 14

when is stem cell therapy more effective?

Answer 14

Where a small and defined cell population is damaged it is more effective.

Question 15

what do bone marrow stem cells form? why might they be needed? how are they collected?

Answer 15

Bone marrow stem cells (haematopoietic stem cells) form blood cells.
If bone marrow is damaged or diseased a stem cell transplant may be needed.
Chemotherapy and radiotherapy, leukaemia often damage it.
Stem cells are collected from a healthy patient with a large needle- painful.
A less painful procedure involves blood being filtered for stem cells and the returned to the patient.

Question 16

what are cord blood stem cells? what are they used for?

Answer 16

Blood stem cells can be taken from cord blood.
Blood from the umbilical cord.
Contains adult stem cells for the blood and immune systems.
Younger and healthier than those in bones.
Used to treat type 1 diabetes.

Question 17

what are intestinal stem cells?

Answer 17

The epithelial lining has a great ability to repair and renew as it contains adult stem cells.

Question 18

what are epidermal stem cells? how are they used?

Answer 18

skin has a great ability to repair and renew as it has adult stem cells.
Can be harvested and used to grow more in a lab.
Layers of new epidermis can be grafted on.

Question 19

how are embryonic stem cells sources? how are they used?

Answer 19

Obtained from embryos in the earliest stages of development (3-5 days old).
Donated by people using IVF.
IVF often produces more embryos than needed.
surplus are stored in a freezer for 5 years and discarded if not needed.
Cultured and allowed to divide rapidly.
Can treat damaged or diseased or injured tissues.

Question 20

what are induced pluripotent stem cells? what can they do?

Answer 20

Adult stem cells that have been genetically reprogrammed to an embryonic state
Not known if there are differences between these and normal ones.
They can make three germ layers.

Question 21

comparisons of ethics with ESCs and ASCs

Answer 21

Embryonic stem cells: used to be destroyed but now can not be damaged.
Adult stem cells: given by people with there consent.

Question 22

what are advantages of ESCs?

Answer 22

Unlimited supply.
Cell division can occur indefinitely.
Can grow in large quantities.
Can differentiate into any type of cell.

Question 23

what are disadvantages of embryonic

Answer 23

Not yet technically possible to train stem cells.
Ethical objections.
Potential for uncontrolled growth. (teratoma formation).

Question 24

what are advantages of adult stem cells?

Answer 24

Already programmed to make a particular cell type and thus can be used for specific treatment.

Question 25

what are disadvantages of adult stem cells?

Answer 25

No indefinite growth.
Limit on cell types which can be formed.
difficult to obtain.
Small number of cells in only some tissues.
Potential for uncontrolled growth.

Question 26

what are advantages of induced pluripotent stem cells?

Answer 26

Use normal somatic cells (many cells available).
Use cells from the person who needs them.
No immune rejection.

Question 27

what are disadvantages of induced pluripotent stem cells?

Answer 27

Time and technology needed to reprogram cells.
May be limited in differentiation capacity.
Not enough knowledge.
Objections to genetic reprogramming.
Potential for uncontrolled growth.