Makindo Medical Notes

Related Subjects: |Anatomy of the Ear |Anatomy of the Oesophagus |Anatomy of the Diaphragm |Anatomy of Large Bowel |Anatomy of Small Bowel |Anatomy of the Biliary system |Anatomy of the Eye |Anatomy of the Larynx |Anatomy of the Ear |Anatomy of Male Genitalia

🦴 Anatomy of Bone Marrow

Bone marrow is a soft, spongy tissue within bones that is vital for haematopoiesis (blood cell production). Two types: Red marrow (active blood cell production) & Yellow marrow (mainly fat storage).

🔎 Types of Bone Marrow

• 🟥 Red Marrow: Produces RBCs, WBCs, platelets. – In adults: sternum, ribs, vertebrae, pelvis, proximal femur/humerus epiphyses. – Abundant in children, decreases with age.
• 🟨 Yellow Marrow: Rich in fat (energy store). – In severe blood loss, can convert → red marrow to aid haematopoiesis.

🏗️ Bone Marrow Structure

• Stroma: Reticular connective tissue, fibroblasts, endothelial cells, adipocytes → supports haematopoiesis.
• Haematopoietic Tissue: Stem/progenitor cells in red marrow → differentiate into blood cell lineages.

🩸 Haematopoiesis

The process of blood cell formation from haematopoietic stem cells (HSCs), which are multipotent and self-renewing.

🌱 Haematopoietic Lineages

• Myeloid Lineage: RBCs, platelets, granulocytes, monocytes. – Erythropoiesis: RBCs → oxygen transport. – Thrombopoiesis: Platelets → clotting. – Granulopoiesis: Neutrophils, eosinophils, basophils → innate immunity. – Monocytopoiesis: Monocytes → macrophages for phagocytosis.
• Lymphoid Lineage: B, T, NK cells. – B cells: Antibody production. – T cells: Cell-mediated immunity. – NK cells: Kill virus-infected/cancerous cells.

⚖️ Regulation of Haematopoiesis

• Erythropoietin (EPO): Kidney-derived, ↑ RBC production during hypoxia.
• Thrombopoietin (TPO): Liver/kidneys → regulates platelets.
• G-CSF: Stimulates neutrophil production (used clinically post-chemotherapy).
• Interleukins: Broad immune regulation.

🏡 Bone Marrow Microenvironment

• Stromal cells + ECM + cytokines create a “niche” regulating HSC self-renewal vs differentiation.

📌 Functions of Bone Marrow

• 🩸 Blood cell production: RBCs, WBCs, platelets.
• 🛡️ Immune response: Produces B & T lymphocytes.
• 🌱 Stem cell reserve: Lifelong pool of HSCs.
• ⚡ Fat storage: Yellow marrow = energy reserve.

⚠️ Clinical Relevance

• 🧪 Bone marrow aspiration/biopsy: Used in diagnosis of leukaemia, anaemia, myelodysplasia.
• 🎗️ Leukaemia: Malignant proliferation of WBC precursors → impaired normal cell production.
• 🚫 Aplastic anaemia: Marrow failure → pancytopenia.
• 🔄 Bone marrow transplant: Stem cell infusion to restore haematopoiesis in cancer/immune disease.
• 🩹 Myelofibrosis: Marrow replaced with scar tissue → anaemia, splenomegaly.

📊 Quick Revision Table

Feature	Red Marrow	Yellow Marrow
Main role	Haematopoiesis	Fat storage (energy)
Location (adults)	Flat bones, epiphyses	Shafts of long bones
Cell content	HSCs, progenitor cells	Adipocytes
Plasticity	Ongoing blood cell production	Can revert to red marrow in severe anaemia/bleeding