Hemopoiesis

• Hemopoiesis


  Formation of blood elements
• Types of hemopoiesis


  • Erythropoiesis
  • Thrombopoiesis
  • Granulopoiesis
  • Monopoiesis
  • Lymphopoiesis
• Hemopoietic tissue


  Produces blood cells
• Early development of RBC production

  1. At the mesoderm of the yolk sac

  2. In the liver and spleen during 2nd trimester

  3. In the bone marrow from 2nd month of intrauterine life

  4. In the bone marrow and thymus for T lymphocytes postnatally
• Lymphoid tissue


  Produces lymphocytes
• Myeloid tissue


  • Produces most formed blood elements
  • Synonymous with red bone marrow from birth onwards
  • Stroma made of reticular fibers and reticular cells (type III collagen)
  • Supplied with sinusoidal capillaries lined with endothelial cells and external perisinusoidal macrophages
  • Newly formed blood cells enter bloodstream by transcellular migration
• Origin of human cells

  1. Zygote -> morula -> blastula -> gastrula

  2. Zygote is totipotent

  3. Cells of trophoblast give rise to placenta and fetal membrane

  4. Inner cell mass are embryonic stem cells (pluripotent)
• Multipotent cells


  Versatile cells that transform into numerous cell types and replicate very fast
• Proerythroblast


  • Spherical and centrally located nucleus occupying 80% of cell
  • Possess fine chromatin granules
  • 1 or 2 prominent nucleoli
  • Basophilic cytoplasm but forms a perinuclear halo
• Basophilic erythroblast


  • Spherical nucleus taking 75% of cell
  • Coarse chromatin (clockface pattern)
• Polychromatophilic erythroblast


  • Nucleus takes 50% of cell
  • Checkerboard chromatin
  • No nucleolus
  • Contains hemoglobin
• Normoblast


  • Eccentric and pyknotic nucleus
  • Contains considerable amount of hemoglobin
  • Pinkish cytoplasm
  • Paucity of organelles
• Reticulocyte


  • Normoblast that has extruded its nucleus
  • Still synthesize hemoglobin
  • Can prematurely enter the bloodstream
• Myeloblast


  • Oval or round nucleus
  • 1-3 nucleoli
  • Fine and even chromatin granules
  • Scanty, moderately basophilic cytoplasm
• Promyelocyte


  • Azurophilic granules
  • Round to oval nuclei with clumped chromatin
• Neutrophilic myelocyte


  • No visible nucleolus
  • Less basophilic than promyelocyte
  • Undergoes up to three mitosis
• Neutrophilic metamyelocyte


  • No longer capable of mitosis
  • Indented nucleus
  • Slightly basophilic
• Stab cell or Band form

  • U or S shaped nucleus
  • 2 lobes
• Eosinophilic myelocyte


  • Clumped chromatin
  • Azurophilic granules
• Eosinophilic metamyelocyte


  • Looks like neutrophilic metamyelocyte except for specific cytoplasmic granules
• Basophilic myelocyte and metamyelocyte


  • Look like neutrophilic counterpart except some granules
  • Nucleus stains less intensely
• Megakaryoblast


  • Large slightly indented ovoid nucleus
  • Loose chromatin material
  • Inconspicuous multiple nucleoli
  • Undergoes 7 incomplete mitosis: endomitosis
• Promegakaryocyte


  • Intermediate stage
  • Several lobes in nucleus
• Megakaryocyte


  • Multilobed nucleus
  • Coarse chromatin
  • Indistinct nuclei
  • Azurophilic granules
• Platelet formation


  Megakaryocytes form pseudopodia that enter sinusoids and they fragment
• Monoblast


  • Large round cell
  • Oval nucleus
  • Fine chromatin granules
  • Resembles myeloblast
• Promonocyte


  • Larger than monoblast
  • Paler staining
  • Chromatin and nucleoli visible
• Lymphopoiesis


  • Occurs in central lymphoid organs (thymus and bone marrow)
  • T cells migrate to thymus while B cells stay in bone marrow
  • In peripheral lymphoid organs, B and T cells remain mitotic ability and undergo mitosis when presented with antigens
  • Recirculating pool of lymphocytes that can migrate via bloodstream
• Lymphoblast


  • Abundant basophilic cytoplasm
  • No azurophilic granules
  • Large and spherical nucleus
  • Fine and dispersed chromatin material
• Prolymphocyte


  • Slightly smaller than lymphoblast
  • Condensed chromatin material
  • Basophilic cytoplasm with azurophilic granules