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									Previous Lecture Summary
    Hematopoiesis and cells of immune
•   Hematopoiesis
    – The process of formation of red and white blood cells
    – Begins in the embryonic yolk sac in the first week of
•   Hematopoietic stem cell
    – A type of cell that gives rise to all types of blood cells
    – Can differentiate into any other cell type
    – Maintain their population level by cell division (self-
    – Are very scarce (1 HSC / 5x104 bone marrow cells)
    – Very difficult to grow in-vitro
                  Types of stem cells

•   Totipotent
    – Cells can give rise to an entire organism e.g. a fertilized egg,
      zygote, Human identical twins develop when totipotent cells
      separate and develop into genetically identical fetuses
•   Pluripotent (also called as Embryonic stems cells /ES)
    – Arise from totipotent cells and can give rise to most but not all
      of the cell types necessary for fetal development e.g. human
      pluripotent cells can give rise to all cell types
•   Multipotent
    – Arise from further differentiation of pluripotent cells, can give
      rise to only a limited number of cell types
•   Unipotent
    – Arise from further differentiation of pluripotent cells, can give
      rise to only same cell type as themselves
                 Progenitor cells

   Multipotent stem cells that have lost the
    capacity for self renewal and are committed
    to a particular cell lineage
   Mainly two lineages:
    • Lymphoid progenitor cells giving rise to B, T and
      NK cells
    • Myeloid progenitor cells giving rise to RBCs,
      many WBCs and megakaryocytes
Hematopoiesis and cells of immune
          Cells of Immune System
•   Granulocytic cells: 3 types based on morphology and
    cytoplasmic staining characteristics:
    • Neutrophils
    • Basophils
    • Eosinophils

•   Monocytes, Histiocytes, Kupffer cells, Microglia,
    Alveolar macrophages, Intravascular Macrophages
•   Dendritic cells

•   Lymphocytes (B and T)
   Multilobed nucleus
   Granulated cytoplasm (stain with both acid and base
   PMN (polymorphonuclear leuckocyte)
   Production in bone marrow
   Life span of only few days in tissues
   Generally first cells to arrive at site of inflammation
   Leukocytosis (increased number of circulating
    neutrophils): a sign of infection
   Extravasation: movement of circulating neutrophils
    into tissues
     • Adherence to vascular endothelium
     • Penetation in the gap between adjacent
       endothelial cells lining the vessel wall
   Chemotactic factors
     • That promote accumulation of neutrophils at
       inflammatory site
     • Components of complement system and blood
       clotting system, many cytokines secreted by Th
       cells and macrophages
   Active phagocytic cells like macrophages
   Primary and secondary granules containing lytic
    enzymes and bactericidal substances
   Primary granules
     • larger, denser, contain peroxidase, lysozyme and
       various hydrolytic enzymes
   Secondary granules
     • smaller, contain collagenase, lactoferrin,
   Granules fuse with phagosomes and cause
   Kill ingested microorganisms
    • Antimicrobial substances (oxygen-dependent
      and oxygen-independent pathways)
          Larger respiratory burst
          more reactive oxygen intemediates
          reactive nitrogen intermediates
          higher expression of defensins

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