1. MLAB 1415- Hematology Keri Brophy-Martinez
Chapter 4 : Hematopoietic Organs

2. Hematopoiesis: overview
Medullary
Origin of blood cells and sequential sites of normal blood production within the bone marrow
Extramedullary
Blood cell production in hematopoietic tissue other than bone marrow
Liver
Spleen
Compensatory mechanism to provide blood cells in times of need

3. Ontogeny (origin) of Hematopoiesis
Begins in mesoderm of yolk sac forming erythroid cells.  Production continues for about six weeks before declining and ends in about two months.
Hemoglobin found in these embryonic cells consist of Gower 1, Gower 2 and Portland.
Fetal liver now assumes responsibility for hematopoiesis during second month.  Yolk sac erythoid cells move to liver and
remain there until the seventh month

4. Ontogeny (origin) of Hematopoiesis
From third to sixth month,
hematopoiesis occurs in
kidney, thymus, spleen and lymph
nodes
Other emerging cells
About three months of life, see platelets
About five months of life, see leukocytes

5. Ontogeny (origin) of Hematopoiesis
Around seventh month of fetal life, hematopoiesis shifts to bone marrow  
Fetal marrow fills with RBCs

6. Ontogeny (origin) of Hematopoiesis
At birth, liver and spleen stop hematopoietic activity.
Bone marrow now becomes active site of hematopoiesis

7. Ontogeny (origin) of Hematopoiesis
Children up to teen years, has hematopoiesis in all bones
Hematopoiesis gradually decreases in shafts of long bones. 
Around age hematopoiesis shifts to production in sternum, ribs, pelvis, vertebrae, and skull. 
After age 40, less area in these sites available for hematopoiesis.

9. Storage Pools Granulocytes and platelets also exist in two pools
Circulating
Marginal

10. Bone Derived Cells
Non-hematopoietic cells involved with bone turnover closely linked with hematopoiesis
Osteoblasts
Responsible for the formation, calcification and maintenance of the bone structure
Large irregularly shaped cells in the bone marrow that may be confused with plasmacytes or malignant cells
Osteoclasts
Responsible for absorption of bone
Assist in degradation of bone
Giant multinucleated, irregularly shaped phagocytic cells in the bone marrow that may be confused with megakaryocytes

11. Bone Derived Cells
Osteoblast
Osteoclast

12. References
Harmening, D. M. (2009). Clinical Hematology and Fundamentals of hemostasis (5th ed.). Philadelphia, PA: F.A. Davis Company.
McKenzie, S. B. (2010). Clinical Laboratory Hematology (2nd ed.). Upper Saddle River, NJ: Pearson Education, Inc..