What Is Bone Marrow, and What Does It Do?

Red bone marrow is involved in hematopoiesis. This is another name for blood cell production. Hematopoietic stem cells that are found in red bone marrow can develop into a variety of different blood cells, including:

• Red blood cells. These are the cells that work to carry oxygen-rich blood to the cells of the body. Old red blood cells can also be broken down in red bone marrow, but this task is mostly performed in the liver and spleen.
• Platelets. Platelets help your blood clot. This prevents uncontrolled bleeding.
• White blood cells. There are several types of white blood cells. They all work to help your body fight off infections.

Newly produced blood cells enter your bloodstream through vessels called sinusoids.

As you age, your red bone marrow is gradually replaced with yellow bone marrow. By adulthood, red bone marrow can be found only in a handful of bones, including the:

• skull
• vertebrae
• sternum
• ribs
• the ends of the humerus (upper arm bone)
• pelvis
• the ends of the femur (thigh bone)
• the ends of the tibia (shin bone)

Yellow bone marrow is involved in the storage of fats. The fats in yellow bone marrow are stored in cells called adipocytes. This fat can be used as an energy source when needed.

Yellow bone marrow also contains mesenchymal stem cells. These are cells that can develop into bone, fat, cartilage, or muscle cells.

Because yellow bone marrow starts to replace red bone marrow over time, most bones in an adult body contain yellow bone marrow.

Bone marrow is crucial for producing blood cells. Therefore, a range of blood-related conditions involve issues with bone marrow.

Many of these conditions affect the numbers of blood cells produced in bone marrow. This causes the conditions to share many common symptoms, including:

• Fever. This can be a result of not having enough healthy white blood cells.
• Fatigue or weakness. This is caused by a lack of hemoglobin, the protein in red blood cells that carries oxygen.
• Increased infections. This is due to having fewer healthy white blood cells, which help fight infections.
• Shortness of breath. A lower red blood cell count can result in less oxygen being delivered to tissues in your body.
• Easy bleeding and bruising. This is due to having fewer healthy platelets, which are important for helping your blood to clot.

Here’s a look at some specific conditions involving bone marrow issues.

Leukemia

Leukemia is a type of cancer that can affect both your bone marrow and lymphatic system.

It happens when blood cells get mutations in their DNA. This causes them to grow and divide more rapidly than healthy blood cells. Over time, these cells start to crowd out the healthy cells in your bone marrow.

Leukemia is classified as either acute or chronic, depending on how fast it progresses. It’s further broken down by the type of white blood cells it involves.

Myeloid leukemia (also known as myelogenous leukemia) involves red blood cells, white blood cells, and platelets. Lymphocytic leukemia involves lymphocytes, a specific type of white blood cell.

Some of the major types of leukemia include:

• acute myeloid leukemia (AML)
• chronic myeloid leukemia (CML)
• acute lymphocytic leukemia (ALL)
• chronic lymphocytic leukemia (CLL)

There’s no clear cause of leukemia, but certain things can increase your risk, including:

• exposure to certain chemicals
• exposure to radiation
• some genetic conditions, such as Down syndrome

Aplastic anemia

Aplastic anemia occurs when bone marrow doesn’t produce enough new blood cells. It occurs due to damage to the stem cells of bone marrow, which makes it harder for them to grow and develop into new blood cells.

This damage can be either:

• Acquired. Exposure to toxins, radiation, or infectious diseases, such as Epstein-Barr or cytomegalovirus, causes the damage. Autoimmune disorders, such as rheumatoid arthritis and lupus, can also sometimes cause aplastic anemia.
• Inherited. A genetic condition causes the damage. An example of inherited aplastic anemia is Fanconi anemia.

Myeloproliferative disorders

Myeloproliferative disorders happen when the stem cells in bone marrow grow abnormally. This can lead to increased numbers of a specific type of blood cell.

There are several types of myeloproliferative disorders, including:

• Primary myelofibrosis. With this condition, red blood cells don’t develop normally and have an unusual shape. It can also cause a decrease in red blood cell production.
• Polycythemia vera. Bone marrow produces too many red blood cells. These extra cells may collect in the spleen, causing swelling and pain. Itching is also a common symptom of polycythemia vera, possibly because of an abnormal histamine release.
• Essential thrombocythemia. Bone marrow produces too many platelets, making blood sticky or thick. This slows down the flow of blood through the body.
• Hypereosinophilic syndrome. Bone marrow produces too many eosinophils. This is a type of white blood cell involved in allergic reactions and destroying parasites. This may lead to itching or swelling around the eyes and lips.
• Systemic mastocytosis. This condition involves having too many mast cells. These are white blood cells that alert infection-fighting blood cells to target specific areas of the body. Having too many mast cells can affect the function of your skin, spleen, bone marrow, or liver.

Bone marrow transplants, also called stem cell transplants, are typically done when people have certain autoimmune diseases or cancers.

During a bone marrow transplant, stem cells are harvested (sometimes from a donor) and eventually transferred into a person living with specific cancers or immunodeficiency disorders. The new stems cells go to work on eradicating cancer cells or other unhealthy cells.

Diseases that may benefit from bone marrow transplants

The diseases that most commonly benefit from bone marrow transplants include:

• lymphomas
• leukemias
• immune deficiency disorders
• multiple myeloma
• severe aplastic anemia

However, because people can experience the same disease differently, bone marrow transplants may not work for everyone. You and your doctor can decide if this therapy is right for you.

Types of bone marrow transplants

There are a few different types of bone marrow transplants. They include:

• Autologous bone marrow transplant. This is when stem cells are harvested from a patient themselves and given back to them after they’ve had intensive treatment.
• Allogeneic bone marrow transplant. A donor who has the same genetic type as a patient — usually a sibling, parent, or unrelated donor — donates their stem cells.
• Umbilical cord blood transplant. Stem cells are taken from an umbilical cord immediately after a baby’s birth. They are then tested and frozen until they’re needed.

Bone marrow transplants can come with side effects and complications, especially when someone is already battling a disease. The treatment’s success rate also depends on a lot of factors, including the:

• overall health of the person
• type of transplant being done
• type of disease

Even with these caveats, bone marrow, or stem cell, transplants can be lifesaving in the right situations.

Bone marrow is found in the bones throughout your body. There are two types of bone marrow. Red bone marrow is involved in the production of blood cells, while yellow marrow is important for fat storage. As you age, yellow bone marrow replaces red bone marrow.

The stem cells found in healthy bone marrow can be lifesaving for people living with certain autoimmune diseases and cancers. Bone marrow transplants, which involve harvesting stem cells and infusing them into people living with certain conditions, have been used in successful treatments since the late 1960s.