Hematopoiesis Overview and Types

Hematopoiesis

• The process of blood cell production, differentiation, and development.
• It takes place to maintain homeostasis.
• Cells of the blood are constantly being lost or destroyed.
• Hematopoiesis is essential for the body’s ability to fight infection and heal wounds.

Sites of Hematopoiesis

• Early life: Yolk sac
• Later on: Bone marrow, liver, spleen

Types of Hematopoiesis

• Medullary hematopoiesis: Hematopoiesis occurs in bone marrow
• Extramedullary hematopoiesis: Hematopoiesis occurs in organs other than bone marrow, such as the liver and spleen.
  • Occurs physiologically during fetal development.
  • Occurs in adults when the bone marrow cannot keep up with the body’s needs.

Stem Cells

• Totipotent: Gives rise to a whole organism
• Pluripotent: Gives rise to the three germ layers of the embryo (endoderm, mesoderm, and ectoderm).
• Multipotent: Gives rise to a limited number of cell types, such as blood cells.

Multipotent (Hematopoietic) Stem Cells

• Undifferentiated and uncommitted stem cells.
• Reside primarily in the bone marrow.
• Ability to self-renew or differentiate into any of the many blood cell types.
• Can differentiate into the myeloid or lymphoid lineages.

Bone Marrow Stroma

• Suitable environment for stem cell growth and differentiation.
• Composed of stromal cells and a microvascular network.
• Stromal cells:
  • Adipocytes
  • Fibroblasts
  • Reticulum cells
  • Endothelial cells
• Extracellular molecules:
  • Collagen
  • Glycoproteins
  • Glycosaminoglycans
  • Growth factors

Hematopoietic Growth Factors (HGF)

• Glycoprotein hormones that regulate proliferation and differentiation of hematopoietic progenitor cells and function of mature blood cells.
• HGFs bind to specific receptors on target cells.
• Activity:
  • Locally: at the site of production by cell-cell contact.
  • Circulate in plasma.

HGF Function

• May bind to the extracellular matrix, forming niches where stem cells can adhere.

Explore the fascinating process of hematopoiesis, which is crucial for blood cell production and maintaining homeostasis. This quiz covers the sites, types, and the roles of stem cells involved in hematopoiesis, helping you understand how the body fights infections and heals itself.