What Is Bone Marrow?

The bone marrow is the spongy part of your bones where oxygen-carrying red bloods, infection-fighting white cells, and clot-forming platelets are made. The bone marrow is a soft tissue with many cavities located at the center of bones. It serves as the primary stem cell manufacturer of the body and participates in fat storage and bone remodeling.

Healthy bone marrow is essential to living. Sickle cell anemia, leukemia, lymphoma, and aplastic anemia are some life-threatening diseases that occur when the bone marrow fails to function properly.

Bone marrow under microscopic staining and examination
Steve Gschmeissner / Science Photo Library / Getty Images

Anatomy of the Bone Marrow

The bone marrow consists of bone cavities, a complex network of blood vessels, and two types of marrow—red marrow and yellow marrow.

Red marrow contains blood stem cells that can become red blood cells, white blood cells, or platelets. These hematopoietic (blood cell forming) stem cells are pluripotent cells (able to produce several types of cells). They are responsible for the production and maintenance of your blood cells.

Yellow marrow is made mostly of fat. It mainly consists of mesenchymal stem cells—multipotent cells found in the supporting tissue surrounding the bone marrow called the stroma. Mesenchymal stem cells have the potential to develop into a number of tissues such as bone, cartilage, and fat.

Function

The primary function of the bone marrow is to manufacture blood cells—red cells, white cells, and platelets. Red blood cells carry oxygen throughout the body, whereas white cells help to fight infections and platelets are necessary for blood to clot.

The cells produced by the bone marrow are:

Most of the immune and blood cells in the body are made in the red bone marrow, whereas cells that lead to the formation of bone, cartilage, and fat are made in the yellow marrow. The bone marrow also participates in bone remodeling, the removal of abnormal cells, and the recycling of cell parts used in the formation of new cells.

The bone marrow makes more than 200 billion new blood cells every day. As you can imagine, it is vitally important to have a properly functioning bone marrow to keep up with the body's demands.

Blood and immune cells constantly undergo processes of renewal and regeneration. For example, red blood cells have a lifespan of about 120 days so they need to be constantly replaced.

Diseases of the Bone Marrow 

The bone marrow may become damaged or malfunction due to:

Many diseases that affect the bone marrow also affect the bone itself, as the bone and marrow work together to regulate bone remodeling.

Bone Marrow Transplants

Bone marrow transplant is the leading treatment and oftentimes the only curative treatment for conditions that threaten bone marrow’s ability to function properly. Bone marrow transplants can help jumpstart or regenerate an immune system by increasing the body’s capacity to produce healthy blood cells.

Because of a person’s unique genetic makeup, a matching donor—oftentimes a family member—needs to be found. If a genetic match is confirmed then bone marrow is harvested and readied for transplant.

A bone marrow transplant may be used to:

  • Treat diseases that have caused bone marrow to stop functioning or function abnormally. Blood disorders such as sickle cell anemia, blood cancers such as leukemia, lymphoma, and genetic conditions that limit or stop the bone marrow from making healthy or functional cells may require a transplant. 
  • Replace damaged bone marrow. High doses of chemotherapy or radiation can damage the bone marrow. The marrow may also be damaged by viral illnesses or possibly by autoimmune disorders. Healthy bone marrow can replace the unhealthy bone marrow and help jumpstart the immune system. 
  • Replace genetically altered bone marrow. Healthy marrow can replace unhealthy, nonfunctional, or largely absent bone marrow in genetic diseases such as Hurler syndrome and adrenoleukodystrophy.

Bone marrow is most commonly harvested from the long bones of the hips and thigh bones although active marrow is can be found inside the spine, shoulder bones, ribs, breastbone, and skull.

When Is a Bone Marrow Transplant Needed?

Malfunctioning bone marrow may present with nonspecific symptoms such as fatigue, easy bruising, unexplained weight loss, or fever. Or, a person may have repeated infections.

When symptoms suggest the bone marrow isn't working properly, doctors conduct a complete medical history and physical exam, which can be followed by a series of tests including a complete blood cell count, which assesses red cells, white cells, and platelets.

If these tests indicate problems, a bone marrow biopsy, genetic screening, and other tests may be done to further explore a diagnosis.

If cancer or another blood disorder is found to be the cause of malfunctioning bone marrow, chemotherapy and/or radiation may be used to eliminate the disease. Once the disease is eradicated a bone marrow transplant may be considered.

Unfortunately, chemotherapy and radiation can sometimes damage the bone marrow and suppress the immune system, simultaneously heightening the potential need for a bone marrow transplant and the risk of its rejection.

Alternative Sources of Stem Cells

There are three other main sources of stem cells that may be used to repopulate the bone marrow:

Peripheral blood stem cells (PBSC): These stem cells circulate in the veins and arteries of all normal people. Patients recovering from chemotherapy and healthy people who are treated with certain drugs that stimulate the growth of the bone marrow have relatively large numbers of PBSC in their blood. The PBSC can be collected and used in certain situations as a source of stem cells for transplantation.

Umbilical cord blood (UCB): Stem cells can be found in the placenta of newborn babies once the umbilical cord is cut. These stem cells have been more frequently used in stem cell transplantation.

Embryos: The use of stem cells is controversial. Ethical reasons have therefore limited their use, although more research is being done to explore its future potential.

Was this page helpful?
Article Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. National Cancer Institute. Bone marrow.

  2. Ullah I, Subbarao RB, Rho GJ. Human mesenchymal stem cells - current trends and future prospective. Biosci Rep. 2015;35(2):e00191. doi:10.1042/BSR20150025

  3. Gulati GL, Ashton JK, Hyun BH. Structure and function of the bone marrow and hematopoiesis. Hematol Oncol Clin North Am. 1988 Dec;2(4):495-511. PMID: 3065314.

  4. Silva A, Anderson AR, Gatenby R. A multiscale model of the bone marrow and hematopoiesisMath Biosci Eng. 2011;8(2):643-658. doi:10.3934/mbe.2011.8.643

  5. Smith AR, Wagner JE. Alternative haematopoietic stem cell sources for transplantation: place of umbilical cord bloodBr J Haematol. 2009;147(2):246-261. doi:10.1111/j.1365-2141.2009.07828.x