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Cell Differentiation. Stem Cells: Unspecialised cells which are capable of proliferation (repeated division via mitosis) and differentiation (development into other specialised cells)

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Cell Differentiation

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Stem Cells:

  • Unspecialised cells which are capable of proliferation (repeated division via mitosis) and differentiation (development into other specialised cells)
  • From cells in inner cell mass (approx 30 cells) eventually all types of specialised cells differentiate (approx 200)
  • Although all cells have the same DNA, as stem cells proliferate, different genes activate. (differentiation)
  • Signals for activation may be:
    • Internal (genes)
    • External (microenvironment- chem. secreted from other cells, physical contacted with other cells and molecules in immediate environment)

Various types of stem cells:

    • Totipotent: potential to create any/all cell types. (found in zygote – 1st five days)
    • Pluripotent: Potential to create foetal cell types (but not embryonic membranes) (found in ICM)
    • Multipotent: Potential to create cell types which are linked by a particular function. (blood stem cell RBC, WBC etc)

Primary Germ layers (pluripotent stem cells)

  • Ectoderm: (closer to body stalk)
      • epidermis of the skin;
      • hair, nails, glands of skin;
      • lens in the eye;
      • receptor cells;
      • epithelium in mouth, nose and anal canal;
      • teeth enamel;
      • nervous system;
      • A. lobe of Pituitary gland, Adrenal medulla;

Primary Germ layers (pluripotent stem cells)

  • Mesoderm: (middle)
      • Skeletal, smooth & cardiac muscles;
      • connective tissues;
      • lymphoid tissues;
      • Endothelium of blood vessels;
      • epithelium of body / joint cavities;
      • kidney, ureter;
      • gonads, reproductive tracts;
      • adrenal cortex;
      • dermis of skin
  • Endoderm (furthest from body stalk)
    • Epithelium of:
      • A.C.;
      • bladder, urethra, gallbladder;
      • pharynx, larynx, trachea, lungs;
      • tonsils, thyroid, thymus glands,
      • Vagina.

Sources of Stem Cells:

1. Adult stem cells

a. Umbilical cord blood & placental

  • multipotent stem cells (can be used to produce blood cells)
  • no harm to mother or child

b. General Adult stem cells

  • mutlipotent stem cells

2. Embryonic

  • pluripotent stem cells
  • requires destruction of embryo

Stem Cell Research:

  • both therapeutic cloning and embryonic stem cell research are permitted in Australian law (as of 2006)

Embryonic Stem Cell research.

  • Cells may be obtained by IVF and are often unused by donors
  • generally 4-5 days old

1. ICM is transferred to culture dish with nutrient solution

2. Cells divide (subculturing) may continue for months

3. Within 6 months 30 cells  millions

  • Cell may also be obtained through therapeutic cloning
    • Nucleus from patients cell inserted into donor egg (minus donor egg nucleus) resulting cell develops into new, identical, blastocyst.

Adult Stem cell Research.

  • Likely that stem cells exist in all body tissues
  • Scientists are trying to discover a way to reintroduce a patients own stem cells into their damaged organs rectifying disease or injury.
  • E.g. Umbilical cord stem cells may be used to help treat conditions such as leukaemia, anaemia and immune system diseases

Ethical Considerations (embryonic research):

  • Positive:
    • Production of replacement tissues and organs may save lives and alleviate suffering
    • Adult stem cell research may take many years to produce practical uses
    • Generally uses surplus IVF embryos which would have been destroyed anyway
    • Embryos used are pre-implanted and could not develop into human life unless implanted. (no difference between using morning after pill or IUD)

Ethical Considerations (embryonic research):

  • Negative
    • Stem cell research is potential but may take many years  many destroyed embryos
    • In future embryos may be produced solely for research  Human embryo trade
    • Routine destruction of embryos desensitising of value of human life
    • Could use adult stem cells which avoids destruction of human life