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Questions and Answers
What is the primary source of new blood cells during normal childhood and adult life?
At which stage of fetal development does the bone marrow become the most important site of haemopoiesis?
What is the term for the process by which the liver and spleen resume their fetal haemopoietic role in certain disease states?
What is the percentage of fat in the marrow of middle-aged adults?
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What is the region of the developing embryo where the stem cells that give rise to definitive haemopoiesis are first observed?
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What is the term for the common precursors of endothelial and haemopoietic cells?
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During which stage of fetal development do the liver and spleen continue to produce blood cells?
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What is the fate of the marrow in the long bones during childhood and beyond?
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Study Notes
Haemopoiesis During Gestation
- Haemopoiesis starts with the embryonic yolk sac through a process called 'primitive haemopoiesis'
- However, the main source of haemopoiesis comes from stem cells in the aorta-gonads-mesonephros (AGM) region
- These stem cells, called haemangioblasts, give rise to endothelial and haemopoietic cells that colonize the liver, spleen, and bone marrow
Haemopoietic Sites During Fetal Development
- From 6 weeks to 6-7 months, the liver and spleen are the primary haemopoietic organs
- The placenta also contributes to fetal haemopoiesis during this period
- From 6-7 months, the bone marrow becomes the main site of haemopoiesis
Haemopoiesis in Childhood and Adult Life
- In childhood and adult life, the bone marrow is the sole source of new blood cells
- Developing cells are located outside bone marrow sinuses, and mature cells are released into the sinus spaces and general circulation
- In infancy, all bone marrow is haemopoietic, but in childhood and adulthood, fatty replacement of marrow occurs in long bones
- In adults, haemopoietic marrow is limited to the central skeleton and proximal ends of the femurs and humeri
Haemopoiesis in Diseased States
- In certain diseases, haemopoiesis can expand down the long bones
- The liver and spleen can also resume their fetal haemopoietic role, known as 'extramedullary haemopoiesis'
- Even in active haemopoietic areas, approximately 50% of the marrow consists of fat in middle-aged adults
- Remaining fatty marrow can revert to haemopoiesis in some diseases
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Description
Learn about the development of haemopoiesis in the embryonic stage, from primitive to definitive haemopoiesis and the role of haemangioblasts. Understand how the liver, spleen, and bone marrow are involved in this process.
