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• Cell replacement theory

  • Technology that relies on replacing diseased or dysfunctional cells with healthy functioning ones
• • cells can be classified as either stem cells or specialised cells
  • stem cell is an undifferentiated cells
• Differentiation is the process by which unspecified cells develop the characteristics and the functions of particular types of cells. such as blood cells, muscle cels, nerve cells etc.
• As a stem cell proliferates, specific genes become activated, which drive the process of differentiation
• • The external signals for cell differentiation include
  • Chemicals secreted by other cells
  • Neighbouring cells physical contact
  • certain molecules in the cell’s immediate surroundings (microenvironment)
• Totipotent- has the potential to become any type of cell and cells of the morula
• Pluripotent- has the potential to become most types of cells inner cell mass of blastocyst
• Multi-potent- has the potential to become some types of cells
• Embryonic stem cells

  • From the inner cell mass of the blastocyst and pluripotent
  • ADV: cells are pluripotent, so can be induced to differentiate into any cell required
  • DADV: Transplanted tissue does not match the patient, so tissue rejection is a possibility and requires the long-term use of immunosuppressant drugs
  • DADV: legal limits to access and potential ethical issues
• Adult stem cells

  • from the foetus, cord blood and your own body for all of your life
  • Cells are multipotent
  • ADV: Many can be harvested relatively easily and differentiated into known type of cells
  • Transplanted tissue does match the patient so tissue rejection is not a concern
  • No ethical issues with using the patient's own cells
  • DADV: Cells are multipotent, and thus have a narrower number of cells that they can be induced to differentiate into
  • Finding and harvesting some types of adult stem cells can be difficult
• The Process

  • Scientists first extract tissue samples from adult tissue/ embryo through biopsy
  • Cells are then transferred to a culture dish containing a nutrient solution where they will then proliferate. Over a few days, the cells will divide, spread over the surface of the culture medium, and begin to fill the dish
  • At this stage cells are removed and placed in several fresh culture dishes ( subculturing) and multiple generations of stem cells proliferate- stem cell line
  • Stem cells then are differentiated into required cells
  • These differentiated cells are then transplanted into the patient
• Induced pluripotent stem cellsBiopsy tissue from patient – usually skin cells or other tissue-specific cells.

  • Culture stem cells in the lab.
  • Reprogram adult stem cells back into an embryonic-like pluripotent state.
  • Culture stem cell lines.
  • Differentiate stem cells into required cells.
  • Transplant tissue into patient.