stem cells

Question 1

what are stem cells?

Answer 1

a stem cell is an unspecialised cell from the embryo, fetus or adult, that…
- under certain conditions, has self-renewal capability by reproducing itself for long periods
- can differentiate whereby unspecialised cells give rise to specialised cells that make up the tissues and organs of the body
- possess large nuclear to cytoplasmic ratio

stem cells are able to replenish their own population and generate cells that travel down various differentiation/developmental pathways

Question 2

what are the 3 unique features of ALL stem cells?

Answer 2

1. stem cells are unspecialised ⮕ stem cells do not have any tissue-specific structures that allows it to perform specialised functions, however unspecialised stem cells can give rise to specialised cells through specialisation/differentiation
2. stem cells are capable of dividing and renewing themselves for long periods ⮕ stem cells may replicate many times in a process called proliferation. if resulting cells continue to be unspecialised, the cells are said to be capable of long-term self renewal by mitotic divisions
3. stem cells can give rise to specialised cells. ⮕ internal (genes become activated & inactivated in a regulated way) & external (chemicals secreted by other cells, physical contact with neighbouring cells etc) signals trigger stem cell differentiation.

Question 3

what is stem cell potency?

Answer 3

stem cell potency refers to the range of cell types to which a stem cell an give rise to.

it reflects the differential potential of the stem cell
it is determined by the number of pathways it can take in its subsequent development through specialisation/differentation

Question 4

what are the 3 basic measures of stem cell potency?

Answer 4

• totipotent
• pluripotent
• multipotent

Question 5

what are totipotent stem cells?

Answer 5

• ☆ totipotent stem cells are master cells of the body that have the ability to give rise to all cell types that make up an organism
• only zygotic stem cells are totipotent.
• totipotent stem cells have the potential to differentiate into any cell type in the adult body to form whole organisms AND any cell of the extra-embryonic membranes
• totipotent stem cells occur at the earliest stage of embryonic development, before the blastocyst stage

Question 6

what are pluripotent stem cells?

Answer 6

• ☆ pluripotent stem cells descend from totipotent stem cells and have the ability to give rise to all types of cells that develop from the three germ layers - mesoderm, endoderm and ectoderm
• they do not have the potential to make differentiated cells that form the extra-embryonic membranes (unlike totipotent stem cells)
• embryonic stem cells (ESCs) are pluripotent stem cells, formed 5-7 days after fertilization

the only known sources of human pluripotent stem cells are those isolated and cultured from inner cell mass of early human embryos and from fetal tissue that was destined to be part of the gonads

Question 7

what are multipotent stem cells?

Answer 7

• ☆ multipotent stem cells are cells that descend from pluripotent stem cells and can differentiate into a limited number of cell types OR many cell lines within a specific type of tissue
• more specialised than totipotent & pluripotent stem cells.
• formed after 7 days upon fertilisation
• blood stem cells are multipotent stem cells from the bone marrow give rise to all the cells of the blood (eg RBC, WBC, platelets), but not to other types of cells
• multipotent stem cells are found in most organs in adult animals, where they can replace dead or damaged cells

Question 8

what are committed stem cells?

Answer 8

• ☆ committed stem cells (includes multipotent & unipotent cells) are those that have a more limited pathway of development compared to pluripotent cells and are destined to produce a specific group of cells
• once committed, stem cells do not switch commitment
• eg the hemangioblast stem cell gives rise to all the blood vessels, blood cells and lymphocytes
• committed stem cells can give rise to more specifically committed stem cells or can generate progenitor cells

Question 9

what are progenitor cells?

Answer 9

• ☆ progenitor/precursor cells are intermediate cell types generated by stem cells before they achieve their fully differentiated state. progenitor cells are partly differentiated cells that divide and give rise to differentiated cells.
• progenitor cells usually show some evidence of differentiation, although the process is not complete until the fully differentiated cell has been formed
• progenitor cells are committed to a limited number of pathways of differentiation/development
• progenitor cells are more limited in developmental pathways than a multipotent stem cell

progenitor cells are derived from committed multipotent cells

Question 10

what is the significance of mitotic division of stem cells?

bro idk how to phrase this lol

Answer 10

mitotic division of stem cells preserves a population of undifferentiated cells while steadily producing a stream of differentiating cells

Question 11

what are the differences between embryonic stem cells and adult stem cells?

Answer 11

• potency ⮕ embryonic stem cells are pluripotent while adult stem cells are multipotent
• ability to culture in lab ⮕ embryonic stem cells are easier to culture compared to adult stem cells
• ethical issues ⮕ adult stem cells are less ethically problematic as not destruction of blastocysts are involved, compared to embryonic stem cells
• potential to differentiate ⮕ embryonic stem cells can become most cells/tissues of the body but most adult stem cells are limited to become specific types of tissue
• use for therapy ⮕ adult stem cells are already used in therapies (eg bone marrow transplant) while embryonic stem cells have great potential for developing future therapies

Question 12

what are the 3 categories of embryonic stem cells?

Answer 12

1. embryonic stem cells (ESCs) ⮕ can be isolated from the inner cell mass (ICM) of the blastocyst
2. embryonic germ cells ⮕ can be isolated from the precursor to the gonads in aborted fetuses
3. embryonic carcinoma cells (FYI)

Question 13

what are the 6 defining properties of embryonic stem cells?

Answer 13

1. ESCs are capable of undergoing an unlimited number of symmetrical divisions without differentiating
2. ESCs exhibit & maintain a stable, full (diploid), normal complement of chromosomes
3. ESCs are clonogenic, meaning a single ESC can give rise to a colony of genetically identical cells
4. pluripotent ESCs can give rise to differentiated cell types that are derived from all 3 primary germ layers (endoderm, ectoderm, mesoderm)
5. ESCs are capable of developing into all fetal tissues during development
6. ESCs are easy to obtain pure and can be cultivated in large numbers, unlike adult stem cells

properties 4, 5 & 6 are unique to ESCs

Question 14

what are primary roles of adult stem cells?

Answer 14

• maintain & repair the tissue in which they are found
• replace cells that die because of injury or disease

Question 15

what is an adult stem cell?

Answer 15

• ☆ an adult stem cell is an undifferentiated cell found amongst differentiated cells in a tissue or organ, and can differentiate to yield the major specialised cell types of the tissue or organ
• adult stem cells are rare. they are dispersed in tissues throughout the mature animal and behave very differently, depending on their local environment. at any time, stem cell numbers in the body are very low, making them very difficult to identify & purify
• the origin of adult stem cells in mature tissues is unknown

Question 16

what are the 3 defining properties of adult stem cells?

Answer 16

1. adult stem cells can make identical copies of themselves for long periods of time - known as long-term self-renewal
2. adult stem cells can give rise to fully differentiated cells that have mature phenotypes, are fully integrated into the tissue and are capable of specialised functions that are appropriate for the tissue
3. adult stem cells are clonogenic

there are a very small number of adult stem cells in each tissue

Question 17

what is hematopoiesis?

Answer 17

hematopoiesis is blood formation. it is a well-studied example of cell differentiation as blood cells at all stages are relatively accessible and can be grown in culture.
hematopoietic stem cells (HSCs) are multipotent stem cells found in blood. their main role is to replace blood cells. there is a population of HSCs located in the bone marrow, and HSCs are derived from the mesoderm in the embryo

Question 18

what are the 3 main lineages from which blood cells are derived?

Answer 18

1. lymphoid lineage ⮕ produces lymphocytes, a type of WBC. B lymphocytes are formed in the bone marrow and make antibodies. T lymphocytes are formed in the thymus and attack foreign cells & regulate immune response
2. myeloid lineage ⮕ gives rise to the rest of the WBCs, including leukocytes. leukocytes perform phagocytosis, identify & destroy cancer cells and remove debris from dead/injured cells
3. erythroid lineage ⮕ yields RBCs (or erythrocytes) and megakaryocytes, which form platelets. erythrocytes transport gases while platelets are for blood clotting functions

Question 19

what are the 3 main sources of human embryonic stem cell lines?

Answer 19

1. cell lines that already exist
2. spare embryos left over from fertility treatments
3. custom made embryos created by somatic nuclear transfer - some argue it’s morally worse to create an embryo with the intention of destroying it in research. but such embryos have a better chance of meeting the needs of patients as they can be produced from a specific patient as a source of cells that are compatible with the patient

Question 20

what are the arguments for and against using spare embryos to harvest ESCs?

Answer 20

FOR
1. destruction of embryos won’t undermine society’s values as embryos have been created & used for IVF with no significant change in how we value human life
2. if it is morally acceptable to use embryos for fertility treatments, it should not be immoral to sacrifice embryos for curing devastating diseases
3. spare embryos would be destroyed anyway once the time limit for keeping them in the freezer has expired; it is better not to waste the embryos but to use them in research that could benefit people.

AGAINST
1. if stem cell therapies become routine treatments, human embryos could be exploited as a source of therapeutic materials, which may indicate a decreasing respect for human life
2. could encourage society to tolerate the loss of life to save a life
3. could be the beginning of a slippery slope leading to dehumanizing scenarios like embryo farms, cloned babies & fetuses used for spared parts

Question 21

what is therapeutic cloning?

not as imp

Answer 21

therapeutic cloning is the creation of stem cells for use in a medical treatment for a particular individual.
therapeutic cloning currently means creating an embryonic stem cell line by a technique called somatic cell nuclear transfer

Question 22

what are the arguments for and against allowing therapeutic cloning?

not as imp

Answer 22

FOR
1. potentially huge benefits to humankind in the future, which outweighs any wrong-doing (destroying embryos)
2. embryonic stem cell lines could be created from the cells of patients suffering rare & complex diseases, creating a vast resource that can be used by many scientists

AGAINST
1. misguided individuals could implant cloned human embryos into a woman’s uterus to create a cloned person
2. commercial pressures and international competition could drive scientists to conduct more and more research on embryos, which would just become a resource for researchers
3. eggs used to create embryos have to be donated by women, who could be exploited for their eggs, especially in poorer countries with fewer legal restrictions

Question 23

what are the arguments for and against embryos having full moral status from fertilization onwards

Answer 23

FOR
1. developmentfrom a fertilized egg into a baby is a continuous and any attempt to pinpoint when personhood begins is arbitrary
2. although an embryo does not currently have the characteristics of a person, it will become a person and should be given the respect and dignity of a person

AGAINST
1. an early embryo that has not yet implanted into the uterus does not have the psychological, emotional or physical properties that are associated with being a person, and therefore doesn’t have any interests to be protected
2. embryos need to be transferred into a woman’s uterus to develop, and the probability that embryos used in IVF will develop into full term successful birth is low. something that could potentially become a person should not be treated as if it actually were a person

Question 24

what are the arguments for and against embryos having full moral status as it develops

Answer 24

FOR
embryos could be given increasing moral status at…
1. 6 days after fertilization as the embryo implants into the uterus
2. around 14 days after fertilization as the primitive streak, the beginnings of the nervous system, starts to appear
3. the phase when the baby could survive if born prematurely
4. birth
a fertilized egg before implantation could be granted a lesser degree of respect than a human fetus of newborn baby
more than half of all fertilized eggs are lost due to natural causes, so using some embryos in stem cell research should not worry people either

AGAINST
1. a person’s life is protected as they are important to the person concerned.
2. if we are not sure whether a fertilised egg should be considered a human being, then we should not destroy it
3. if we judge the moral status of the embryo from its age, then we are making arbitrary decisions about who is human. eg if formation of nervous system marks the beginning of personhood, then a patient who has lost nerve cells in a stroke has become less human? no right

Question 25

what are arguments for and against the embryo having no moral status at all

Answer 25

FOR
1. fertilised human eggs are just parts of other people’s bodies until they have developed enough to survive independently. if we destroy a blastocyst before implantation into the uterus we don’t harm it as it has no beliefs, desires, expectations, aims or purposes to be harmed

AGAINST
1. taking embryonic stem cells out of an early embryo prevents it from developing in its normal way, meaning it is prevented from becoming a human being

Question 26

what are iPSCs?

Answer 26

iPSCs (induced pluripotent stem cells) are specialised adult cells that can be reprogrammed to an embryonic stem cell-like state by introducing genes important for maintaining essential properties of embryonic stem cells

iPSCs don’t involve destroying embryos :)

Question 27

what are the benefits and challenges of using iPSCs in future therapies?

Answer 27

benefits: since iPSCs are made from the patient’s own cells, it is hoped that reprogramming can provide a source of patient-specific specialised cells that would be recognized by the body and won’t be rejected
challenges: producing tailor-made cells wold be a time-consuming, slow, and likely expensive process

Question 28

what are safety challenges of using iPSCs?

Answer 28

• iPSCs & ESCs can self renew indefinitely and this property must be turned off to prevent tumours from forming
• reprogramming technqiues that involve manipulating genes inside the cells may be affected by the age of cells they are made from
• since cells made are patient-specific, standardization will be a challenge

Question 29

what are considerations regarding accessibility of iPSCs stem-cell-based therapy?

Answer 29

1. such therapies would need a well-developed healthare system with the necessary infrastructure for producing & distributing the cells, with highly trained specialists to manage & develop treatments
2. ESC-based therapies may not be made available to patients in countries where use of cells from early embryos is viewed as morally unacceptable