There are 2 main types of stem cells – embryonic and adult.
1 – EMBRYONIC STEM CELLS
Embryonic stem cells (ESCs) are present only during the earliest periods of human life development, around 5 days after the egg is fertilized. As a result they are obtained from embryos formed by eggs which have been fertilized in the lab and donated for research purposes.
Embryonic stem cells are pluripotent. This means that they can divide and develop into all types of specialized cell in the human body. Because of this ability, embryonic stem cells hold the most potential for regenerative medicine. However, the FDA limits their use due to ethical issues and scientific challenges like the potential for the transmission of genetic diseases, tissue rejection and controlling how they differentiate.
2 – ADULT STEM CELLS
Adult stem cells appear as the fetus grows and remain present in the body for the rest of the person’s life. These stem cells are able to self-renew for many years and give rise to more adult stem cells.
Adult stem cells are multipotent and tissue-specific. This means that they divide and develop only into the specialized cells of the tissues they live in. These adult stem cells are found in the bone marrow, fat tissue, skin, muscles and intestines.
Adult stem cells include hematopoietic stem cells and mesenchymal stem cells.
a – HEMATOPOIETIC STEM CELLS
Hematopoietic stem cells (HSCs) or blood forming stem cells give rise to many erythrocytes (red blood cells), leukocytes (white blood cells) and platelets every day. There are several types of hematopoietic stem cells and the most common is the hematopoietic stem cell (HSC-CD 34+). HSCs do not decrease in number as we age and they are responsible for tissue regeneration.
b – MESENCHYMAL STEM CELLS
Mesenchymal stem cells (MSCs) which are also known as marrow stromal cells, are obtained from fat tissue and the bone marrow. MSCs have the ability to form osteoblasts (bone forming cells), chondrocytes (cartilage forming cells), myocytes (muscles forming cells) and adipocytes (fat cells). MSCs reduce in number as we age. Studies suggest that they have a vital role of prepping the microenvironment to ensure that the hematopoietic cells are better able to do their work.