Hematopoiesis and Erythropoiesis Process

Hematopoiesis

Hematopoiesis is the process by which blood cells are produced in the body. It involves the development of different blood cell types from hematopoietic stem cells.

Erythropoiesis

• Process by which red blood cells (erythrocytes) are produced
• Regulated by erythropoietin (EPO), a hormone produced by the kidneys
• Erythropoiesis occurs in the bone marrow
• Stages of erythropoiesis:
  1. Commitment of hematopoietic stem cells to erythroid lineage
  2. Erythroblast formation
  3. Hemoglobinization
  4. Maturation of reticulocytes
  5. Release of mature erythrocytes into the bloodstream

Stem Cell Development

• Hematopoietic stem cells (HSCs) are the precursor cells that give rise to all blood cell types
• HSCs have the ability to self-renew and differentiate into various blood cell lineages
• Stem cell development is regulated by a complex interplay of cytokines, growth factors, and transcription factors

Leukopoiesis

• Process by which white blood cells (leukocytes) are produced
• Includes the development of granulocytes (neutrophils, eosinophils, and basophils) and agranulocytes (lymphocytes and monocytes)
• Regulated by cytokines such as granulocyte-colony stimulating factor (G-CSF) and granulocyte-macrophage colony-stimulating factor (GM-CSF)

Thrombopoiesis

• Process by which platelets are produced
• Regulated by thrombopoietin (TPO), a hormone produced by the liver and kidneys
• Thrombopoiesis occurs in the bone marrow
• Stages of thrombopoiesis:
  1. Commitment of hematopoietic stem cells to megakaryocyte lineage
  2. Maturation of megakaryocytes
  3. Platelet production and release into the bloodstream

Lymphopoiesis

• Process by which lymphocytes are produced
• Includes the development of B cells and T cells
• Regulated by cytokines such as interleukin-7 (IL-7) and stem cell factor (SCF)
• Lymphopoiesis occurs in the bone marrow and lymphoid organs (e.g., spleen, lymph nodes)

Granulopoiesis

• Process by which granulocytes (neutrophils, eosinophils, and basophils) are produced
• Regulated by cytokines such as G-CSF and GM-CSF
• Granulopoiesis occurs in the bone marrow
• Stages of granulopoiesis:
  1. Commitment of hematopoietic stem cells to granulocyte lineage
  2. Maturation of granulocyte precursors
  3. Release of mature granulocytes into the bloodstream

Hematopoiesis

• Process by which blood cells are produced in the body, involving development of different blood cell types from hematopoietic stem cells

Erythropoiesis

• Process by which red blood cells (erythrocytes) are produced
• Regulated by erythropoietin (EPO), a hormone produced by the kidneys
• Occurs in the bone marrow
• Stages: commitment of hematopoietic stem cells to erythroid lineage, erythroblast formation, hemoglobinization, maturation of reticulocytes, and release of mature erythrocytes into the bloodstream

Stem Cell Development

• Hematopoietic stem cells (HSCs) are precursor cells that give rise to all blood cell types
• HSCs have the ability to self-renew and differentiate into various blood cell lineages
• Regulated by a complex interplay of cytokines, growth factors, and transcription factors

Leukopoiesis

• Process by which white blood cells (leukocytes) are produced
• Includes development of granulocytes (neutrophils, eosinophils, and basophils) and agranulocytes (lymphocytes and monocytes)
• Regulated by cytokines such as granulocyte-colony stimulating factor (G-CSF) and granulocyte-macrophage colony-stimulating factor (GM-CSF)

Thrombopoiesis

• Process by which platelets are produced
• Regulated by thrombopoietin (TPO), a hormone produced by the liver and kidneys
• Occurs in the bone marrow
• Stages: commitment of hematopoietic stem cells to megakaryocyte lineage, maturation of megakaryocytes, and platelet production and release into the bloodstream

Lymphopoiesis

• Process by which lymphocytes are produced
• Includes development of B cells and T cells
• Regulated by cytokines such as interleukin-7 (IL-7) and stem cell factor (SCF)
• Occurs in the bone marrow and lymphoid organs (e.g., spleen, lymph nodes)

Granulopoiesis

• Process by which granulocytes (neutrophils, eosinophils, and basophils) are produced
• Regulated by cytokines such as G-CSF and GM-CSF
• Occurs in the bone marrow
• Stages: commitment of hematopoietic stem cells to granulocyte lineage, maturation of granulocyte precursors, and release of mature granulocytes into the bloodstream

Blood Composition

• Blood is a specialized type of connective tissue composed of plasma (matrix) and formed blood elements (cells)
• Formed blood elements include:
  • Red blood corpuscles (RBCs)
  • White blood cells (WBCs) or leukocytes (granular and agranular)
  • Blood platelets

Blood Smear Preparation

• Giemsa's stain (methylene blue + eosin) is used to differentiate blood cells by their nuclei and cytoplasmic granules
• Blood count:
  • RBCs count
  • Total leukocytic count
  • Platelets count
  • Differential leukocytic count (percentage of each type of leukocyte relative to the total number of WBCs)

Myeloid Tissue Structure

• The stroma:
  • Reticular fibers: support myeloid cells and endothelial cells
  • Stromal cells:
    • Reticular cells: produce reticular fibers and growth factors
    • Macrophages: phagocytosis of aged RBCs and malformed blood elements
    • Fat cells: one of the largest cells in bone marrow
• The myeloid cells:
  • Pluripotent hemopoietic stem cells (PHSCs): give rise to daughter cells
  • Multipotent hemopoietic stem cells (MHSCs): give rise to cell colonies for each formed blood element
  • Colony forming units (CFUs): CFU-Ly, CFU-GEMM, CFU-E, CFU-Meg, CFU-M, CFU-G, CFU-Eo, CFU-Ba

Hemopoiesis

• Definition: The process of formation of different blood elements
• Site:
  • During embryonic life: yolk sac, liver, spleen, and bone marrow
  • In children: bone marrow of all bones
  • In adults: restricted to the marrow of the sternum, ribs, skull, vertebrae, pelvis, and sacrum

Red Blood Corpuscles (RBCs)

• Average RBC count: 5-5.5 millions/mm³ in males, 4.5-5 millions/mm³ in females
• Life span of RBCs: 100-120 days
• Function: oxygen transport
• Shape: eosinophilic biconcave discs
• Nucleus: absent
• Cytoplasm: hemoglobin is more concentrated at the periphery

Erythropoiesis

• First recognizable erythrocyte precursor
• Hemoglobin synthesis is most active
• Hemoglobin is accumulating
• STOP Cell Division
• The synthesis of hemoglobin is completed

Blood Platelets

• Normal count: 150,000-400,000/mm³
• Function: formation of a blood clot
• Structure:
  • Shape: biconvex discs
  • Nucleus: absent
  • The granulomere: granular central core contains granules
  • The hyalomere: pale basophilic area at the periphery

Thrombopoiesis

• Definition: The formation of blood platelets
• Release of mature platelets from the bone marrow into the bloodstream