Bone Marrow: Facts, Types & Pathology

Picture of Bone marrow

What is Bone marrow?

Bone marrow is the flexible tissue in the interior of bones. In humans, red blood cells are produced by cores of bone marrow in the heads of long bones in a process known as hematopoiesis. On average, bone marrow constitutes 4% of the total body mass of humans; in an adult having 65 kilograms of mass (143 lbs), bone marrow typically accounts for approximately 2.6 kilograms (5.7 lb). The hematopoietic component of bone marrow produces approximately 500 billion blood cells per day, which use the bone marrow vasculature as a conduit to the body’s systemic circulation. Bone marrow is also a key component of the lymphatic system, producing the lymphocytes that support the body’s immune system.

Bone marrow transplants can be conducted to treat severe diseases of the bone marrow, including certain forms of cancer such as leukemia. Additionally, bone marrow stem cells have been successfully transformed into functional neural cells, and can also potentially be used to treat illnesses such as inflammatory bowel disease.

Fast facts on Bone marrow

Here are some key points about bone marrow. More detail and supporting information is in the main article.

  • A bone marrow transplant can save the lives of people battling leukemia, lymphoma and other blood cancers.
  • At birth, all bone marrow is red. As humans age, red marrow increasingly begins to convert to yellow marrow.
  • In adults, around half of the bone marrow is red and half is yellow.
  • 200 billion new red blood cells are made by the bone marrow every day, along with white blood cells and platelets.
  • Around 1% of the body’s red blood cells are regenerated every day.
  • Healthy bone marrow manufactures between 150,000 and 450,000 platelets per microliter of blood, the amount of blood that fits on the head of a pin.
  • Bone marrow contains mesenchymal and hematopoietic stem cells.
  • Around 10,000 people in the US are diagnosed each year with diseases that require bone marrow transplants.
  • 7 out of 10 people who require a bone marrow transplant do not have a matching donor in their family, and rely on the registry of bone marrow donors to find a match.
  • The process for matching a patient with a donor involves comparing human leukocyte antigen (HLA) types in order to find a match.
  • Several diseases, many of which are incurable, pose a threat to bone marrow and prevent bone marrow from turning stem cells into essential cells.

Picture of Bone marrow

Types of Bone marrow

There are two types of bone marrow:

  • red marrow that is responsible for producing red blood cells, white blood cells and platelets
  • yellow marrow consisting mainly of fat cells

There are a number of blood vessels and capillaries traversing through the marrow making it a very vascular organ.

At birth and in early childhood most of the marrow is red. As a person ages more and more of it is converted to the yellow type. About half of adult bone marrow is red.

What does Bone marrow do for your body?

The majority of red blood cells, platelets, and most of the white blood cells are formed in the red marrow. Yellow bone marrow produce fat, cartilage and bone.

White blood cells survive anywhere from a few hours to a few days, platelets for about 10 days, and red blood cells for about 120 days. These cells must be constantly replaced by the bone marrow as each blood cell has a set life expectancy.

Certain conditions may trigger additional production of blood cells, such as when the oxygen content of body tissues is low, if there is loss of blood or anemia, or if the number of red blood cells decreases. In such cases, the kidneys produce and release erythropoietin, a hormone that stimulates the bone marrow to produce more red blood cells.

Similarly, the bone marrow produces and releases more white blood cells in response to infections, and more platelets in response to bleeding. If a person experiences serious blood loss, yellow bone marrow can be activated and transformed into red bone marrow.

Bone marrow Pathology and Diagnosis

Certain diseases of the bone marrow like leukemia, multiple myeloma, myelodysplastic syndrome (MDS), pancytopenia, anemia etc. require examination of the bone marrow tissue. This is called bone marrow aspiration or bone marrow biopsy. A needle is used to withdraw samples of the marrow from within the bone. This is often a very painful process.

Bone marrow is suppressed with the use of cancer chemotherapy. This leads to severe drop in production of RBCs (leading to anemia), WBCs (leading to increased risk of life threatening infections) and platelets (leading to risk of bleeding tendencies).

With advent of medical science it is possible now to transplant the bone marrow in diseased individuals. This process has shown success in a number of cancer patients.

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