What is Bone Marrow?

Bone marrow is the soft spongy tissue that lies within the hollow interior of long bones. In adults, marrow in large bones produces new blood cells. Bone marrow forms around 4% of total body weight (around 2.6 kg in a healthy adult).

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.

Functions of bone marrow

Red blood cells (erythrocytes) carry oxygen to the tissues.

Platelets or thrombocytes (derived from megakaryocytes) help prevent bleeding and aid in clotting of blood.

Granulocytes (neutrophils, basophils and eosinophils) and macrophages (collectively known as myeloid cells) fight infections from bacteria, fungi, and other parasites. They also remove dead cells and remodel tissue and bones.

B-lymphocytes produce antibodies, while T-lymphocytes can directly kill or isolate invading cells.

RBC live for around 170 days and rest are shorter lived and need to be replenished continuously. An average human requires approximately one hundred billion new hematopoietic cells each day. This is performed by the Hematopoietic Stem Cells (HSCs).

Bone marrow and stem cells

Around the central bore of the bone or the central sinus lie the Mesenchymal stem cells. These cells have the capacity to form various cells of the body including osteoblasts (that form bones), chondrocytes (that form cartilage), myocytes (that form muscles) and other cells. Apart from this there are the endothelial stem cells that form blood vessels.

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.

Further Reading

Last Updated: Jun 21, 2023

Dr. Ananya Mandal

Written by

Dr. Ananya Mandal

Dr. Ananya Mandal is a doctor by profession, lecturer by vocation and a medical writer by passion. She specialized in Clinical Pharmacology after her bachelor's (MBBS). For her, health communication is not just writing complicated reviews for professionals but making medical knowledge understandable and available to the general public as well.


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  1. Djaíne Da Conceição Dantas Djaíne Da Conceição Dantas Brazil says:

    Obrigado. Estava precisando muito saber das funções da medula óssea.

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