6.5- Stem Cells Flashcards
What is differentiation?
The process of cells becoming specialised.
What are stem cells?
Undifferentiated cells- aren’t adapted to a particular function and have the potential to differentiate.
-able to undergo cell division repeatedly = source of new cells necessary for growth, development and tissue repair.
- once specialised they lose ability to divide, entering G0 phase.
Activity has to be strictly controlled:
- slow division = leads to ageing, tissue isn’t replaced efficiently.
- uncontrolled division= tumors (mass of cells)= cancer.
What is meant by potency?
A stem cell’s ability to differentiate into different cell types.
The greater the number of cell types it can differentiate into, the greater its potency.
What are the 3 potency levels/types?
- Totipotent stem cells- can differentiate into any type of cell. ( eg. Fertilised egg/zygote. Eventually forms whole organism)
- Pluripotent stem cells- can form all tissue types but not whole organisms. Present in early embryos.
- Multipotent stem cells- can only form a range of cells within a certain type of tissue. (Eg. Haematopoetic stem cells in bone marrow)
Why is differentiation important?
In multicellular organisms cells have to specialise in order to take on different roles in tissues and organs.
When cells differentiate they become adapted to their particular role and this is based on the function of the tissue, organ and organ system.
All blood cells are derived from stem cells in the bone marrow.
Explain the replacement of red and white blood cells.
RBCs:
Mammalian erythrocytes are essential for transport of O2 around the body.
- due to lack of nucleus/organelles= life span is only 120 days so they need to be replaced constantly.
- stem cells in bone marrow produce 3 billion erythrocytes per kg of body mass a day to meet demand.
Neutrophils:
- essential role in immune system. Live for only 6 hours.
- stem cells produce 1.6 billion per kg per hour. This increases during infection.
What are the sources of animal stem cells?
- Embryonic stem cells:
- present at early stage of embryo development.
- totipotent.
- after 7 days, blastocyst (mass of cells) is formed. Cells are now pluripotent. Remain in this state in fetus until birth. - Tissue/adult stem cells:
- present throughout life from birth. Multipotent.
- can be harvested from umbilical cords of newborns. Advantage as plentiful supply of umbilical cords and no surgery needed. Can be stored for future as they wouldn’t be rejected in a transplant for that individual.
What are the sources of plant stem cells?
Meristematic tissue (meristems):
- present wherever growth is occurring. Tips of roots and shoots.
- located between phloem and xylem tissues= called vascular cambium.
Cells in this region differentiate into the different cells present in the xylem/phloem as this ensures that vascular tissue grows as plant grows.
-pluripotent.
What are the uses of stem cells?
Potential of treating:
- heart disease- muscle tissue in heart is damaged.
- type 1 diabetes- insulin producing cells can be injected.
- Parkinson’s disease- caused by death of dopamine.
- Alzheimer’s disease- brain cells destroyed.
- macular degeneration- causes blindness in elderly.
- birth defects.
- spinal injuries.
Already used in:
- treatment of burns(can produce new skin).
- drug trials.
-development biology.
What are the ethical problems of using stem cells?
- Removal of stem cells from embryos causes destruction of the embryos.
- Religious objections- life begins at contraception so destruction of the embryo is murder.
lack of consensus as to whether embryo itself has rights and who owns the genetic material being used.
Use of plant/adult stem cells and those from umbilical cords overcome these issues to a decent extent, however, these cells are multipotent not pluripotent like embryonic stem cells.
