Hematopoiesis

• What is hematopoiesis?

  A controlled, continuous, and regulated process of blood cell production.
• What are the key components involved in hematopoiesis?

  • Cell renewal
  • Proliferation
  • Differentiation
  • Maturation
• What is the outcome of hematopoiesis?

  It results in the formation and development of mature and functioning cells in the blood.
• What type of cells are allowed to circulate in the blood?

  Only mature cells are allowed to circulate in our blood.
• Why should hematopoiesis never stop?

  Because the body needs a continuous supply of blood cells.
• How does the body regulate blood cell production?

  The body produces what it needs, no more, no less.
• What is the chief site of the mesoblastic phase of hematopoiesis?

  The yolk sac.
• When does the mesoblastic phase begin?

  As early as the 19th day of gestation.
• What type of cells are produced during the mesoblastic phase?

  • Erythroblasts (immature or primitive red blood cells)
• What is hemoglobin composed of?

  Hemoglobin is made up of 4 units of heme paired with a globin.
• What is thalassemia?

  An inherited blood disorder caused when the body doesn’t make enough hemoglobin.
• What are the types of embryonic hemoglobins present during the mesoblastic stage?

  • Gower I Hemoglobin
  • Gower II Hemoglobin
  • Portland Hemoglobin
• What are the globin contents of Gower I Hemoglobin?

  2 Epsilon globin chains and 2 Zeta globin chains.
• What are the globin contents of Gower II Hemoglobin?

  2 Alpha globin chains and 2 Epsilon globin chains.
• What are the globin contents of Portland Hemoglobin?

  2 Zeta globin chains and 2 Gamma globin chains.
• What is the chief site of the hepatic phase of hematopoiesis?

  The liver.
• When does the hepatic phase begin?

  At 5 to 7 gestational weeks.
• What types of cells are produced during the hepatic phase?

  • Developing erythroblasts
  • Granulocytes
  • Monocytes
  • Lymphoid cells
  • Megakaryocytes
• What is the most predominant hemoglobin during the hepatic stage?

  Hemoglobin F (HbF).
• How long is HbF abundant after delivery?

  For the first 6 months after delivery.
• What are the globin contents of Hemoglobin F (HbF)?

  2 Alpha globin chains and 2 Gamma globin chains.
• What is the characteristic of Hemoglobin A (HbA) during pregnancy?

  It is present in little amounts during pregnancy.
• When does HbA become abundant?

  Beyond 6 months of delivery.
• What are the types of Hemoglobin A (HbA)?

  • HbA1 (95%): 2 Alpha globin chains and 2 Beta globin chains
  • HbA2 (2-3%): 2 Alpha globin chains and 2 Delta globin chains
• What percentage of HbF is still present in adults?

  1. 2% of HbF is still present in adults.
• What is the chief site of the medullary phase of hematopoiesis?

  The bone marrow.
• When does the medullary phase occur?

  From the 5th to 6th month of gestation.
• What types of cells are produced during the medullary phase?

  • Hematopoietic cells that give rise to mature RBCs, WBCs, and platelets
• What are HSCs?

  Hematopoietic stem cells that give rise to blood cells.
• What is the inner part of the bone called?

  The bone marrow.
• What is the principal source of blood cell production in adults?

  The flat bones (e.g., sternum, ribs, pelvis).
• What is retrogression in the context of bone marrow?

  Replacement from red to yellow bone marrow (active to inactive).
• What are the characteristics of red bone marrow?

  • Active
  • Composed of hematopoietic cells and macrophages
  • Arranged in extravascular cords
  • Functions: production of blood cells, iron storage, B-cell development
• What are the characteristics of yellow bone marrow?

  • Inactive (not capable of producing cells)
  • Accumulation of fats
  • Can become active again if there is increased demand for blood cells
• What are the classifications of bone marrow cellularity?

  • Normocellular: 30-70% hematopoietic cells
  • Hypercellular (Hyperplasia): >70% hematopoietic cells
  • Hypocellular (Hypoplasia): <30% hematopoietic cells
  • Aplastic (Aplasia): very few or total absence of hematopoietic cells
• What is the function of the nutrient artery?

  It supplies blood only for the bone marrow.
• What is the function of the periosteal artery?

  It provides nutrients for both the bone and the bone marrow.
• What is the role of the hematopoietic microenvironment?

  • Nurtures and protects HSCs
  • Balances quiescence, self-renewal, and differentiation of HSCs
• What are the functions of stromal cells in the hematopoietic microenvironment?

  • Supply semifluid matrix (stroma)
  • Excrete extracellular matrix for cell adhesion
  • Regulate HSCs and maintain proteins needed by maturing cells
• What are the types of stromal cells and their functions?

  • Endothelial cells: regulate particle flow
  • Adipocytes: secrete steroids influencing erythropoiesis
  • Macrophages: phagocytosis and cytokine secretion
  • Osteoblasts: bone-forming cells
  • Osteoclasts: bone-resorbing cells
  • Reticular cells: support vascular sinuses and hematopoietic cells