Stem cells come from several primary sources, broadly categorized into embryonic and adult origins: Embryonic Stem Cells:

• Derived from embryos that are about 3 to 5 days old, specifically from the inner cell mass of a blastocyst, which is a hollow ball of about 150 cells formed after the fertilized egg (zygote) divides multiple times

• These cells are pluripotent, meaning they can differentiate into almost any cell type in the human body

• Embryonic stem cells are often obtained from embryos created via in vitro fertilization (IVF) and donated for research with informed consent

Adult Stem Cells:

• Found in small quantities in various tissues throughout the body, including bone marrow, peripheral blood, fat (adipose tissue), brain, skin, blood, umbilical cord blood, and other organs like liver, pancreas, and cornea

• These cells are typically multipotent, meaning they can differentiate into a limited range of cell types related to their tissue of origin

• Bone marrow is a rich source of hematopoietic stem cells (which give rise to blood cells), and these cells are commonly harvested from the iliac crest of the pelvis

• Adult stem cells can also be collected from peripheral blood through a process called apheresis

• Umbilical cord blood and tissue are additional sources of stem cells, often collected at birth

Other Sources:

• Emerging research suggests potential stem cells in amniotic fluid and baby teeth, though these are less established sources

• Scientists are also exploring ways to create stem cells through genetic reprogramming of other cell types

In summary, stem cells originate from early-stage embryos (embryonic stem cells) and from various tissues in the fetus, newborn, and adult body (adult stem cells), with bone marrow, blood, fat, and umbilical cord being key adult sources