Stem cells: Types, What they are and what they do

What is stem cell?

While cells in the body serve a purpose, stem cells can be used to become any type of cell.

Stem cells can be defined as undifferentiated cells that are capable of transforming into specific cells when the body requires them.

Scientists and doctors are fascinated by stem cells because they can help explain how certain functions work and sometimes how they go wrong.

Stem cells are also promising in treating certain diseases for which there is no cure.

Stem cells sources

Two main sources of stem cells are adult tissues and embryos. Scientists are also looking for ways to create stem cells from other cells using genetic “reprogramming”.

Stem cells for adults

Throughout a person’s life, stem cells are present in their body. These stem cells can be used by the body whenever it requires them.

Adult stem cells are also known as tissue-specific stem cells or somatic stem cells. They exist in every part of the body, even before an embryo is born.

Although they are not in a specific state, the cells are more specialized than embryonic stem cells. They will remain in this state until they are needed for a specific purpose (e.g., skin or muscle cells).

Every day, the body renews its tissues. Stem cells are found in certain parts of the body such as the gut or bone marrow. They constantly divide to create new tissues that can be used for repair and maintenance.

Different types of tissue contain stem cells. Researchers have discovered stem cells in a variety of tissues, including:

  • The brain
  • Bone marrow
  • Blood and blood vessels
  • Skeletal muscles
  • Skin
  • The liver

But stem cells are not easy to find. They can remain non-specific and non-dividing for many years before the body calls them to grow or repair new tissue.

Adult stem cells are capable of self-renewing or dividing indefinitely. They can create different cell types or regenerate the original organ.

These divisions and regeneration are what heal a skin injury or allow an organ like the liver to repair itself after damage.

Scientists believed that adult stem cells could not differentiate based upon their origin tissue. Some evidence suggests they can also differentiate to other types of cells.

Embryonic stem cell transplants

An embryo is formed at the very beginning of pregnancy after the sperm fertilizes eggs.

The embryo forms a blastocyst, or ball of cells, around 3-5 days after fertilization by sperm.

The blastocyst is a source of stem cells that will be later implanted in the womb. A blastocyst is approximately 4-5 days old.

Scientists take embryo stem cells from embryos. These are often extra embryos that result in in vitro fertilization (IVF).

Doctors in IVF clinics fertilize multiple eggs in a test tube to make sure at least one egg survives. To start a pregnancy, they will only implant a small number of eggs.

These cells form a single cell when sperm fertilizes eggs.

The single-celled zygote begins to divide and form 2, 4, 8, 16, and so forth. It is now an embryo.

This mass of approximately 150-200 cells will be the blastocyst shortly after the embryo implants in your uterus. Two parts make up the blastocyst.

  • An outer cell mass that is part of the placenta
  • An inner cell mass which will eventually develop into the human body

The embryonic stem cells can be found in the inner cell mass. These cells are called totipotent by scientists. These cells are totipotent because they can develop into any type of cell in the body.

The right stimulation can make cells blood cells, skin cells and all other types of cells that the body requires.

The blastocyst stage lasts about five days in early pregnancy before the embryo implanted in the uterus or womb. This stage is when stem cells start to differentiate.

Embryonic stem cell differentiation can lead to more types of cells than adult stem cells.

Mesenchymal stem cells, (MSCs),

MSCs are made from connective tissue, or stroma, that surrounds the body’s organs and other tissues.

Scientists have used MSCs in the creation of new tissues such as bone, cartilage and fat cells. They could one day be used to solve a variety of health problems.

Induced pluripotent stem cell (iPS).

These cells are created in a laboratory using skin cells and other tissue-specific cell types. These cells behave in the same way as embryonic stem cells and could be used to develop a variety of therapies.

But, it is important to continue research and develop.

Scientists first take stem cells from an embryo or adult tissue in order to grow them. These cells are then placed in controlled cultures where they can divide and reproduce, but not further specialize.

A stem-cell line is a collection of cells that have been grown in controlled conditions and are capable of reproducing and dividing.

Researchers can share stem-cell lines and manage them for different purposes. They can also stimulate stem cells to become more specific. This is called directed differentiation.

It has been difficult to grow large numbers embryonic stem cells. This is because it was easier than growing adult stem cells. Scientists are now making progress with both types of cells.

Different types of stem cells

According to the potential of stem cells to differentiate into other types, researchers classify them.

The most powerful embryonic stem cells are those that can transform into any type of cell in your body.

The complete classification is:

Totipotent: These stem cells can be differentiated into any type of cell. When the zygote begins to divide, only a few cells will appear. These are totipotent.

Pluripotent: These cells can transform into any type of cell. Pluripotent cells are formed from embryos in the beginning.

Multipotent: These cells can become a close-related family of cells. For example, adult hematopoietic cells can differentiate into red blood cells and platelets.

Oligopotent: These cells can differentiate into several cell types. This can be done by adult lymphoid stem cells or myeloid stem cells.

Unipotent: These cells can only make one type of cell, and that is their own. They are stem cells, however, because they can regenerate themselves. Adult muscle stem cells are an example.

Because embryonic stem cells cannot be part of extra-embryonic membranes and the placenta, they are considered pluripotent rather than totipotent.


Although stem cells are not designed to serve a single purpose, they can be used for many purposes.

First, stem cells can be stimulated to take on any role, and can also regenerate tissue damaged under the right conditions.

This potential could save lives, repair injuries and restore tissue damaged after an injury or illness. Scientists are exploring many potential uses of stem cells.

Tissue regeneration

The most important use for stem cells is tissue regeneration.

A person needing a new kidney had to wait until a donor was available and then have a transplant.

Although there is a shortage in donor organs, scientists can instruct stem cells to differentiate in certain ways to allow them to grow specific types of tissue or organs.

To make new skin tissue, doctors can use stem cells found just below the skin’s surface. This tissue can be used to repair severe burns or other injuries, and the new skin will then grow back.

Treatment for Cardiovascular Disease

A team of researchers at Massachusetts General Hospital published PNAS early edition in 2013 describing how they created blood vessels using human stem cells in laboratory mice.

After 2 weeks, the stem cells were implanted and networks of blood-perfused vessels formed. These new blood vessels were as good as natural ones.

These authors hoped that the technique would eventually be used to treat patients with cardiovascular or vascular disease.

Brain disease treatment

One day, doctors may be able use replacement cells and tissues in the treatment of brain diseases such as Alzheimer’s and Parkinson’s.

Parkinson’s disease, for instance, results in uncontrolled muscle movements due to damage to brain cells. Scientists may use stem cells to repair the brain tissue. This could restore the brain cells that control uncontrolled muscle movements.

These types of treatments have been proven promising by researchers who have successfully differentiated embryonic stem cells.

Therapy for cell deficiency

Scientists are hopeful that one day they will be able to create healthy heart cells in a lab and transplant them into patients with heart disease.

These cells can repair damage to the heart by repopulating it with healthy tissue.

People with type 1 diabetes may also be able to receive pancreatic cell transplants to replace insulin-producing cells their immune systems have destroyed or lost.

Only one treatment is currently available: a pancreatic transplant. Very few pancreases are available.

Treatments for blood diseases

Adult hematopoietic cells are now used routinely by doctors to treat certain diseases such as sickle cell anemia and leukemia.

Hematopoietic stem cell are found in blood and bone and can make all types of blood cells, including red blood cells that carry oxygen that fights disease and white blood cells.

Stem cells can be donated or harvested

Stem cells can be donated by people to support a loved one or for their own future use.

These are some of the sources that can make donations:

Bone marrow These cells are usually taken from the pelvic or hip bone. The stem cells are then taken from bone marrow by technicians for donation or storage.

Stem cells for peripheral nerves One person is given several injections to cause stem cells to be released into their bloodstream. The blood is then removed from the body. A machine separates the stem cells and doctors return the blood.

Umbilical cord blood After delivery, stem cells can be taken from the umbilical cord without causing harm to the baby. Some people donate cord blood while others keep it.

Although this stem cell harvesting can be costly, the benefits for future use include:

  • The stem cells can be easily obtained
  • There is less likelihood of tissue transplant rejection if it comes directly from the recipient.

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