Hematopoiesis

• What is hematopoiesis?

  The continuous, regulated process of renewal, proliferation, differentiation, and maturation of all blood cell lines.
• What are the main phases of hematopoietic development?

  Mesoblastic phase, hepatic phase, and medullary (myeloid) phase.
• What is the lifespan of red blood cells (RBCs)?

  120 days.
• What is the role of hematopoietic stem cells (HSCs)?

  They are capable of self-renewal and directed differentiation into all required cell lineages.
• What are the objectives of the chapter on hematopoiesis?

  To define hematopoiesis, describe blood cell evolution, predict active marrow, relate hematopoiesis to organs, explain stem cell theory, discuss cytokines, describe morphologic changes, define apoptosis, and discuss therapeutic applications.
• What are the sites of hematopoiesis during fetal development?

  • Yolk sac
  • Fetal liver
  • Thymus
  • Spleen
  • Bone marrow
• How does hematopoiesis differ in adults compared to developing humans?

  In adults, hematopoiesis is primarily restricted to the bone marrow, while in developing humans, it occurs in various sites including the yolk sac and fetal liver.
• What is the significance of the hepatic phase in hematopoiesis?

  It is characterized by the production of megakaryocytes and fetal hemoglobin (Hb F) as the predominant hemoglobin.
• When does medullary (myeloid) phase hematopoiesis begin?

  Between the fourth and fifth month of fetal development.
• What is the myeloid-to-erythroid ratio during the myeloid phase?

  The ratio gradually approaches 3:1 to 4:1, which are normal adult levels.
• What are the components of adult hematopoietic tissue?

  • Bone marrow
  • Lymph nodes
  • Spleen
  • Liver
  • Thymus
• What is the primary lymphoid tissue responsible for T and B lymphocyte development?

  The bone marrow and thymus.
• What is the role of stromal cells in the bone marrow?

  They provide structural support and regulate hematopoietic stem and progenitor cell survival and differentiation.
• What is the composition of normal bone marrow?

  It contains red marrow (hematopoietically active) and yellow marrow (hematopoietically inactive).
• What happens to the active marrow as a person ages?

  Active marrow is gradually replaced by adipocytes, leading to an increase in yellow marrow.
• What is the significance of marrow cellularity?

  Marrow cellularity typically decreases with age, indicating the ratio of hematopoietic cells to adipocytes.
• What are the types of cells found in red marrow?

  • Hematopoietic cells
  • Stromal cells
  • Blood vessels (arteries, veins, vascular sinuses)
• What are the main types of stromal cells in the bone marrow?

  Endothelial cells, adipocytes, macrophages, lymphocytes, osteoblasts, osteoclasts, and reticular adventitial cells.
• What is the function of the extracellular matrix in the bone marrow?


  It serves to anchor developing hematopoietic cells in the bone cavity.
• How do endothelial and reticular adventitial cells contribute to hematopoiesis?

  They separate hematopoietic cells from the lumen of vascular sinuses and provide structural support.
• Where do poietic cells develop?

  In specific niches within the cords.
• What are erythroid precursors also known as?

  Erythroblasts.
• Where are more mature erythroblasts located in relation to vascular sinuses?

  Adjacent to the outer surfaces of the vascular sinuses.
• What is the composition of normal adult bone marrow?

  50% hematopoietic cells and 50% fat.
• What are the main components of bone marrow?

  • Hematopoietic cells
  • Stromal cells
  • Blood vessels (arteries, veins, vascular sinuses)
• What type of cells originate from mesenchymal cells in the bone marrow?

  Stromal cells.
• What is the role of endothelial cells in the bone marrow?

  They regulate the flow of particles entering and leaving hematopoietic spaces in the vascular sinuses.
• What do adipocytes secrete that affects hematopoiesis?

  Cytokines or growth factors that positively stimulate HSC numbers and bone homeostasis.
• What is the function of macrophages in the bone marrow?

  Phagocytosis and secretion of cytokines that regulate hematopoiesis.
• What are osteoblasts and osteoclasts responsible for?

  Osteoblasts are bone-forming cells, while osteoclasts are bone-resorbing cells.
• What is the structure of the hematopoietic microenvironment or niche?

  • Nurtures and protects HSCs
  • Regulates quiescence, self-renewal, and differentiation
  • Involves complex signaling networks
• What is the primary role of the nutrient artery in the bone marrow?

  To supply blood only to the marrow.
• How does blood exit the marrow?

  Via the central longitudinal vein.
• What are the key functions of the liver?

  • Protein synthesis and degradation
  • Coagulation factor synthesis
  • Carbohydrate and lipid metabolism
  • Drug and toxin clearance
  • Iron recycling and storage
  • Hemoglobin degradation
• What is the anatomical arrangement of hepatocytes in the liver?

  They are arranged in radiating plates emanating from a central vein.
• What role do Kupffer cells play in the liver?

  They remove senescent cells and foreign debris from the blood.
• What is extramedullary hematopoiesis?

  • Production of blood cells outside the bone marrow
  • Occurs in response to infectious agents or pathologic conditions
• Where is the spleen located in the body?

  Underneath the diaphragm behind the fundus of the stomach in the upper left quadrant of the abdomen.
• What are the three types of splenic tissue?

  • White pulp
  • Red pulp
  • Marginal zone
• What is the function of the red pulp in the spleen?

  It acts as a filter for blood passing through the region.