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L12 - STEM CELLS I Describe the roles, fates and process of…

- - - - Extraembryonic
      - Embryonic tissue (Embryo Proper)
        
        Pluripotent
        
        Produce all the somatic cell types
        
        Cannot differentiate into extramebryonic tissue
        
        *E.g. Embryoblasts = Pluripotent Embryonic Stem cells
        
        Multipotent
        
        Produce specific somatic cell types
        
        E.g. Multipotent cells of the Ectoderm/Endoderm/Mesoderm
        
        Bipotent
        Able to differentiate into two cell types
        E.g. Myotube cell
        
        Unipotent
    - - E.g.Gametes
        Terminally differentiated, they cannot differentiate in isolation of one another.
    - - Haematopoietic Stem cells are considered to have High Potency
  - - - Assymmetric cell divison cause an unequal distribution of cytosolic contents which produces differentiated progeny
      - Symmetric cell division results fom equal division of intracellular material.
        
        CAUSE PROLIFERATION OF PARENT CELL TYPE
- - - - Hepatocytes
        
        Remarkable Capacity to regenerate
        
        Technically "compenatory hypertrophy" - not regeneration
        
        Can regrow to original size after 70% reduction
        
        Remnant tissue grows to recover original mass & function in <2 weeks
        
        Almost all hepatocytes re-enter S phase, proliferate and differentiate (G0)
      - Fbroblasts
      - Some smooth muscle cells
    - - Typically mature cells are terminaly differentaited
        
        Potential Issues with tissue structure if not terminally differentiated
        
        Would the syncitium of cells in muscle types be jeopardised if they divided throughout our life?
        
        Reactivated neurons that divide, would that nterfer with synapses,
      - Homeostasis of Terminally Differentiated Cells
        
        Most adult tissues contain tissues pecific
        stem cells in reversible G0
        (quiescence)
        
        Maintain cellular homeostasis for
        the organism’s lifespan.
        
        Tissue damage (external stimuli)
        
        Activation of SCs àundergo immense
        
        Proliferation
        
        Differentiation
        
        Regeneration
        
        Uncontrolled Stem Cell Replication is cancerous
        
        Hayflick's Limit desribes the limitations to cell division
        
        Telomere Shortening
        
        Mutation Accumulation
        
        DNA replication is imperfect
        
        Relationship between cancer risk and number of stem cell divisions in different tissue types is proportional
        
        Limiting stem cell proliferation safeguards against cancerous replication
        
        Asymmetric division allows progeny to rapidly differentiate and regenerate tissue