M01.10.12 Bone Marrow

Bone marrow is the primary hematopoietic organ responsible for the production of blood cells. It exists in two forms: red marrow (active in hematopoiesis) and yellow marrow (inactive, primarily composed of adipose tissue). In adults, red marrow is localized to the axial skeleton and proximal ends of long bones.

Structure of Bone Marrow

1. Stroma

• The supportive framework is composed of:
  • Reticular cells (produce reticular fibers)
  • Adipocytes (store energy and regulate the bone marrow environment)
  • Fibroblasts, macrophages, and endothelial cells

2. Hematopoietic Cells

• Includes three primary lineages:
  • Erythroid lineage: Produces red blood cells.
  • Myeloid lineage: Produces granulocytes, monocytes, and platelets.
  • Lymphoid lineage: Gives rise to B and T lymphocytes.

3. Sinusoids

• Thin-walled blood vessels that allow newly formed blood cells to enter the bloodstream.
• Lined by a single layer of endothelial cells supported by a thin basement membrane.

Histological Appearance

• Red Bone Marrow:
  • Rich in hematopoietic cells.
  • High cellularity with erythroid islands (clusters of erythroblasts around a central macrophage).
  • Presence of megakaryocytes (large cells responsible for platelet production).
• Yellow Bone Marrow:
  • Predominantly composed of adipocytes.
  • Sparse hematopoietic activity.

Age-Related Changes

• At birth, all bone marrow is red, transitioning to yellow with age as hematopoietic demand decreases.
• By adulthood, red marrow is retained in flat bones (e.g., sternum, ribs, pelvis) and the epiphyses of long bones.

Points to Remember

• Bone marrow is the primary site of blood cell production.
• It consists of stromal cells, hematopoietic cells, and sinusoids.
• Red marrow is active in hematopoiesis, while yellow marrow serves as an energy reserve.
• Histological identification relies on the cellularity and presence of adipocytes.

Clinical Relevance

• Bone Marrow Biopsy: Used to diagnose conditions like leukemia, anemia, or myelofibrosis.
• Bone Marrow Transplant: A treatment for hematologic malignancies or bone marrow failure.

Bibliography

1. Gartner, L. P., & Hiatt, J. L. (2020). Color Textbook of Histology. Elsevier.
2. Mescher, A. L. (2021). Junqueira’s Basic Histology: Text and Atlas. McGraw-Hill Education.
3. Ross, M. H., & Pawlina, W. (2020). Histology: A Text and Atlas. Lippincott Williams & Wilkins.

Normal bone marrow,

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Normal bone marrow,

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Normal bone marrow smear,

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Normal bone marrow smear,

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Normal bone marrow smear,

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Normal bone marrow smear with plasma cells,

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Normal bone marrow smear with megakaryocyte,

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