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Origin, Development and Anatomy of Blood and Blood-forming Organs


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Types of Hematopoiesis     
  1. Medullary Hematopoiesis: Bone Marrow
  2. Extramedullary hematopoiesis: Outside of the marrow. Also made in the liver and spleen

Hematopoiesis in the Embryo and Fetus 

  1. Mesoblastic period: yolk sac
             fetus 1-2 months
  1. Mesenchyme cells: undifferentiated precursor of all tissues. Give rise to fat, cartiledge, bone.
  2. Blood island surrounded by endothelial cells
  3. Blood cells (free) in lumen of primiti

Hematopoiesis in the Embryo and Fetus


        2. Hepatic Period: Liver and spleen

Liver and spleen starts to differentiate to lymphocytes.

  • Liver 80%
  • spleen 20%

Hematopoiesis in the Embryo and Fetus


         3. Myeloid period: bone marrow

  • Gone into the bone  and start to make blood
  • monocytes and megakarocyte


  1.  Axial
  2. Appendicular
  1. Adult (top of humerus, femur, peliv,sternum, cranium, vertebral skeletal always making blood)
  • PSIC
  • ASIC, spinal processes or vertebral bodies
  • Sternum
  • 1-2 ml bone marrow aspirated


  •  Red Bone Marrow


  • Actively producing RBC, WBC, platelets



  • Yellow Bone marrow 
  • Full of fat
  • In emergencies fat can change to RBC
Anatomy of Bone
  1. Cancellous: spongy bone "trabeculae"
  • hematopoietic cord
  • marrow sinus "space"
  • central vein
  • Granulocyte, megakaryocyte,and erythroblast seen

Indications for Bone Marrow Studies:


  • Primary hematologic disease 
  • Anemia, erthrocytosis, polycythemia
  • Leukopenia & leukocytosis
  • Immature of abnormal cells in circulation
  • Thrombocytopenia & thrombocytosis

Indications for Bone Marrow Studies:


  • Secondary hematologic disease 
  • Solid malignant tumors that metastasize to bone marrow (i.e. Ovarian, lung cancer)
  • Disseminated bacterial, fungal, or protozoan infections

Bone marrow aspirate examination:


1. Estimation of cellularity


  • Red bone marrow (RBC, WBC, and thrombocyte precursors) vs. yellow bone marrow (fat cells); normally 50% red marrow in adult
  • Myeloid: Erythroid (M:E ratio)
    • ratio of WBC precursors and mature WBC vs. RBC precursors
    • M:E ra

Bone marrow aspirate examination:


2. Differential nucleated cell count 


  • bone marrow is prepared for examination
  • coverslip and slide prep are stained to differentiate types of formed elements
  • 1000 nucleated cells (WBC & RBC) are counted

Nucleated Cell differential and reporting
  • Pronormoblasts 0-1.5
  • Basophilic nomoblasts 0-5
  • Polychromatophilic normoblast 5-30
  • Orthochromatic normoblasts 5-10

Bone marrow aspirate examination:


3. Iron stores and special stains
  • Wright Giemsa

Reticuloendothelial System (RE)

(mononuclear, phagocytic) 

  • fixed macrophages: tissue cells (spleen)
  • free macrophages: connective tissue
  • endothelial cells
  • circulating monocytes: in the blood stream, leave in 12 hrs and become macrophages

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