Types of Human Stem Cells

Types of Human Stem Cells

• Totipotential Cells:
  • Present shortly after fertilization
  • Most versatile, can develop into all human cell types, including fetus
• Pluripotential Stem Cells:
  • Develop a few days post-fertilization
  • Can differentiate into any cell type except fetal development
• Multipotential Stem Cells:
  • Derived from pluripotential cells
  • Found in adults, limited to forming specific cell types
  • Example: Bone marrow produces various blood cells, cartilage, and adipose tissue

Stages of Hematopoiesis

• Mesoblastic Stage:
  • Begins around the 19th day of gestation in yolk sac blood islands
  • Active for 8-12 weeks, mainly focused on erythropoiesis
  • Involves embryonic hemoglobin types: Gower 1, Gower 2, and Portland
• Hepatic Stage:
  • Occurs in the 3rd month of gestation, shifting hematopoiesis to the fetal liver
  • By the 4th month, primitive cells decrease as definitive erythroblast, granulocytes, and megakaryocytes emerge
  • Spleen, thymus, and lymph nodes become active in hematopoiesis
  • Hemoglobin present: Hemoglobin F, Hemoglobin A1, Hemoglobin A2
• Myeloid/Medullary Stage:
  • Takes place between the 5th and 6th month of gestation as bone marrow becomes primary hematopoiesis site
  • At birth, bone marrow is the dominant source of cell production
  • Hematopoiesis happens in most bones, primarily in flat bones (e.g., sternum, ribs, vertebrae)

Bone Marrow Structure and Function

• One of the largest organs, consisting of hematopoietic cells, fat tissue, and stroma
• Red marrow: Active in cell production
• Yellow marrow: Contains fats, inactive in cell production
• Red marrow can regress into yellow marrow
• Marrow contains immature cells that mature into functional blood cells

Cellular Elements of Bone Marrow

• Pluripotential stem cells initiate hematopoietic cell generation and maturation
• Multipotential hematopoietic stem cells serve as the progenitor for all blood cells

Hematopoietic Cell Phases

• Primitive/Multipotential Cells:
  • Most immature, capable of self-renewal and differentiation into all blood cells
• Intermediate Cells:
  • Committed progenitor cells on the path to distinct lineages
• Mature Cells:
  • Fully developed with specific functions, seen in peripheral blood
  • Granulocytes include basophils, eosinophils, and neutrophils

Examination of Maturing Cells

• General cellular characteristics include overall cell size and nuclear-cytoplasmic (N:C) ratio
• Nucleus contains DNA and genetic information; chromatin changes from loose to clumped structure during maturation
• Cytoplasm stains basophilic (deep blue) indicating protein presence
• Hematopoietic growth factors (cytokines) stimulate or inhibit precursor cell production, including Colony Stimulating Factors (CSF) and Colony Forming Units (CFU)