2 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)
3 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)
4 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;
5 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 skinEndoderm (furthest from body stalk)Epithelium of:A.C.;bladder, urethra, gallbladder;pharynx, larynx, trachea, lungs;tonsils, thyroid, thymus glands,Vagina.
6 Sources of Stem Cells: 1. Adult stem cells a. Umbilical cord blood & placentalmultipotent stem cells (can be used to produce blood cells)no harm to mother or childb. General Adult stem cellsmutlipotent stem cells2. Embryonicpluripotent stem cellsrequires destruction of embryo
7 Stem Cell Research: Embryonic 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 donorsgenerally 4-5 days old1. ICM is transferred to culture dish with nutrient solution2. Cells divide (subculturing) may continue for months3. Within 6 months 30 cells millionsCell may also be obtained through therapeutic cloningNucleus from patients cell inserted into donor egg (minus donor egg nucleus) resulting cell develops into new, identical, blastocyst.
8 Adult Stem cell Research. Likely that stem cells exist in all body tissuesScientists 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
9 Ethical Considerations (embryonic research): Positive:Production of replacement tissues and organs may save lives and alleviate sufferingAdult stem cell research may take many years to produce practical usesGenerally uses surplus IVF embryos which would have been destroyed anywayEmbryos used are pre-implanted and could not develop into human life unless implanted. (no difference between using morning after pill or IUD)
10 Ethical Considerations (embryonic research): NegativeStem cell research is potential but may take many years many destroyed embryosIn future embryos may be produced solely for research Human embryo tradeRoutine destruction of embryos desensitising of value of human lifeCould use adult stem cells which avoids destruction of human life