Bone Marrow: Types, Locations, Functions, and Transplantation

Bone marrow is the soft, vascular tissue filling bone cavities, existing in two interconvertible forms:

Red Marrow (Myeloid Tissue)

• Function: Hematopoiesis — produces erythrocytes, leukocytes, platelets.
• Location: Axial skeleton (skull, ribs, sternum, vertebrae, pelvis) and proximal epiphyses of long bones (femur, humerus) in adults; all bones in children.
• Cellularity: 40–60% hematopoietic cells; rest fat, stroma, vessels.

Yellow Marrow (Adipose Tissue)

• Function: Energy storage (triglycerides); can revert to red marrow under hypoxic/erythropoietin drive.
• Location: Diaphyses of long bones (femur, humerus) in adults.
• Conversion: Red → yellow with age; yellow → red in severe anemia, high altitude, EPO therapy.

Clinical Significance

• Biopsy/aspiration: Posterior iliac crest (gold standard for hematologic diagnosis).
• Transplantation: Autologous (myeloma, lymphoma) or allogeneic (leukemia, aplastic anemia, immunodeficiency). HLA matching critical.
• Donation: Peripheral blood stem cells (mobilized with G-CSF) now >90% of donations; marrow harvest under GA alternative.