Lecture Notes on Hematopoiesis

Introduction to Hematopoiesis

• Definition: Production of blood cells in the body, not just red blood cells.
• Terminology:
  • Hematopoiesis: All blood cells (formed elements).
  • Erythropoiesis: Specifically red blood cells (erythrocytes).

Key Concepts

• Stem Cells:
  • Hematopoietic stem cells are the precursors for all blood cells.
  • Characteristics:
    • Pluripotent: Can differentiate into various cell types.
    • Self-replicating: Maintains a stem cell population.

Site of Hematopoiesis

• Location:
  • In adults: Primarily in red bone marrow.
  • In utero: Begins in yolk sac, moves to liver and spleen by 3 months gestation, and finally to red bone marrow at birth.
  • By adulthood, red bone marrow is primarily found in the axial skeleton (e.g., skull, sternum, vertebral column, pelvis, ends of long bones).

Bone Marrow Changes with Age

• At approximately 20 years old, about 50% of red bone marrow converts to yellow bone marrow (fat).

Lineages in Hematopoiesis

1. Lymphoid Lineage:

   • Produces lymphoid progenitor cells.
   • Results in:
     • Natural Killer (NK) Cells: Part of the innate immune system, target and kill infected cells.
     • Lymphoblasts: Can mature into T cells (in thymus) and B cells (in bone marrow).
       • B Cells: Mature in the bone marrow; produce antibodies as plasma cells.
       • T Cells: Mature in the thymus and can become T-helper cells or cytotoxic T cells.

2. Myeloid Lineage:

   • Produces myeloid progenitor cells.
   • Results in:
     • Erythrocytes (Red Blood Cells):
       • Begins as Proerythroblasts → Erythroblasts → Reticulocytes → Mature Erythrocytes.
     • Granulocytes: Myeloblasts differentiate into:
       • Neutrophils: First responders to infection.
       • Basophils: Involved in allergic responses.
       • Eosinophils: Important in fighting parasitic infections.
     • Monocytes:
       • Circulating form (monocyte) turns into macrophage upon entering tissues.
     • Megakaryocytes: Produce platelets (thrombocytes) through thrombopoiesis.

Regulation of Erythropoiesis

• Erythropoietin (EPO):
  • A hormone released by kidneys to stimulate erythropoiesis in response to low oxygen levels in the blood.
  • Acts on precursor cells in the bone marrow to increase production of red blood cells.

Summary of Processes

• Hematopoiesis: General process of blood cell production.
• Erythropoiesis: Specific process for red blood cell production.
• Thrombopoiesis: Process for platelet production.
• Key Nutrients: Vitamin B12, folate, and iron are essential for red blood cell production.

Conclusion

• Understanding hematopoiesis is crucial for insights into blood disorders and overall health.
• For further information, refer to additional lectures and resources.