Stem cells are able to repair and replace damaged tissues and organs, and research on the use of these remarkable cells to treat many otherwise incurable conditions is ongoing. In this lesson, we’ll learn what stem cells are and how they are being used in medicine.
Definition of a Stem Cell
Stem cells are the cells that are capable of forming the entire human body.
They’re amazing since the very beginning of life, a fertilized egg cell divides repeatedly to form a group of stem cells that will go on to eventually make all the organs and tissues in your body. Stem cells are also present in adults, where they play an important role in repairing and replacing damaged cells and tissues.The main feature of a stem cell is that it can divide to give rise to both more stem cells and also specialized cells like nerve cells or muscle cells. No other type of cell can do this! In this way, stem cells replenish themselves at the same time that they provide new specialized cells to create or repair organs and tissues.
Types of Stem Cells
There are several different types of stem cells, and they have different abilities and functions. Totipotent stem cells have the ability to differentiate into every type of cell in the body. These are only found in very early embryos and disappear later in fetal development. Pluripotent stem cells are also found only in embryos and are able to form almost all of the types of cells in the body.
At later stages of fetal development, and even in adults, there are stem cells known as multipotent, which means that they are able to form several types of specialized cells that are in closely related families of cells. For example, mesenchymal stem cells can give rise to cells that make up all types of connective tissues, like muscle, bone, and cartilage. This is a type of multipotent stem cell, because it can divide to produce several types of related cells, but it could never produce a cell of a different type, such as a nerve cell or liver cell.
Take a look at this image.
This is a hematopoietic stem cell in the bone marrow, which can differentiate into all of the blood cells (red and white) in the body. Other types of stem cells in the bone marrow can differentiate into connective tissue, like muscle and bone, or to nervous tissue.
Embryonic Stem Cells
When a human egg cell is fertilized, it begins to divide immediately, and all of the cells in this very young embryo are totipotent stem cells. Within a few days, the dividing cells have formed a hollow structure called a blastocyst. Within the blastocyst, cells in one region group together to form an inner cell mass. This inner cell mass contains all the pluripotent stem cells that will make up the developing fetus, and eventually, create an adult human being.
Medical Uses of Embryonic Stem Cells
Embryonic stem cells can be taken from the inner cell mass and cultured in a laboratory. It is thought that these cells might eventually be able to be used to treat patients with serious illnesses and injuries, like spinal cord injuries and diabetes, and research is ongoing to develop stem cell therapies for such patients. The goal of this research is that stem cells could be induced to differentiate into the cells that were damaged by the injury or disease, and then implanted into the patient to replace the damaged tissues.This research is very controversial and also has serious safety issues. Since embryonic stem cells are pluripotent, they can divide into almost any type of cell.
If they’re simply injected into a patient, they will not necessarily develop into the proper cells and may instead form a tumor or cause further damage to the patient. If methods could be developed to control the differentiation of stem cells, however, this could provide a treatment for many diseases and injuries that are now thought to be incurable.
Adult Stem Cells
Some multipotent stem cells are present in most body tissues in children and adults.
These stem cells differentiate into specialized tissue cells to repair and replace damaged tissue. There is also a large concentration of multipotent and even some pluripotent stem cells present in the bone marrow. The concentration of bone marrow stem cells is highest in young children and declines with age.
Medical Uses of Adult Stem Cells
Unlike embryonic stem cells, adult stem cells are already in use in medicine. In patients with certain types of blood and bone marrow cancers (leukemia, lymphoma, etc.
) and certain other disorders such as aplastic anemia or hereditary immune deficiencies, bone marrow transplants are used to replace the bone marrow stem cells of a patient. In this procedure, the immune system and bone marrow stem cells of the patient are destroyed by radiation or high-dose chemotherapy. Then, new bone marrow stem cells are infused into the patient to repopulate the immune system with healthy cells. This is a successful procedure that has been used clinically for over 50 years. It is not free of risks, however. Patients must take immune suppressant drugs to prevent rejection of the bone marrow graft, and in some cases, the transplant is unsuccessful even with these drugs.Mesenchymal stem cells, which can differentiate into connective tissues like muscle and bone and cartilage, have also been used in orthopedic applications to repair damaged cartilage in the knee.
This is a new therapy, but it has shown some promise in treating cartilage injuries that do not heal on their own. Research is currently being conducted on various other types of adult stem cells with the hope that they could eventually be used to repair spinal cord injuries and heart damage following a heart attack, and treat autoimmune diseases like Type 1 diabetes.Because adult stem cells are present in the bone marrow of all adults and children, they are easy to obtain. Recently, stem cells have also been extracted from adipose (fatty) tissue, which is easier and less painful to remove than bone marrow. The use of adult stem cells in medicine is also much less controversial than the use of embryonic stem cells. For these reasons, the majority of research into medical applications of stem cells is being conducted on adult stem cells, despite their inability to differentiate into all types of cells in the body.
..Stem cells are the cells that are capable of forming the entire human body and are found in both embryos and adults.
In the embryo, stem cells are totipotent, which means they can form all of the cells in the body, or pluripotent, able to form almost all of the cells in the body. In children and adults, stem cells are likely to be multipotent, able to form several types of related cells, but not all types of body cells. In children and adults, the majority of stem cells are found in the bone marrow, although some stem cells can be found in most tissues and organs. Adult stem cells are used clinically now in bone marrow transplants and to repair damaged knee cartilage.
Research into other uses of both adult and embryonic stem cells is ongoing and will hopefully lead to treatments for many currently incurable disorders, such as spinal cord damage, heart damage, and many autoimmune disorders.