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    Related Topics

    From Lymphatic System

    Lymph Nodes
    Small structures that filter lymph and store immune cells.
    Pharyngeal Tonsil
    Located in the nasopharynx (adenoids).
    SALT
    Skin-associated lymphoid tissue.
    Deep Cervical Lymph Nodes
    Located along internal jugular vein; receive lymph from head and neck.
    Tracheobronchial Nodes
    Drain lungs and bronchi.
    Lymphatic Capillaries
    Initial lymphatic vessels that collect interstitial fluid.
    BALT
    Bronchus-associated lymphoid tissue.
    Retroaortic Nodes
    Located behind the aorta.
    Submental Lymph Nodes
    Drain the floor of the mouth and central lower lip.
    Cisterna Chyli
    Dilated sac at the start of the thoracic duct.
    Subscapular Axillary Nodes
    Located along the posterior chest wall.
    Popliteal Lymph Nodes
    Drain the foot and leg.
    Waldeyer’s Ring
    Ring of lymphoid tissue surrounding the naso- and oropharynx.
    Axillary Lymph Nodes
    Drain the upper limbs and chest wall.
    Pectoral Axillary Nodes
    Located along the anterior chest wall.
    Mastoid Lymph Nodes
    Drain the posterior scalp and ear.
    Anterior Mediastinal Nodes
    Drain anterior thoracic structures.
    Superficial Cervical Lymph Nodes
    Drain superficial structures of the head and neck.
    Thoracic Duct
    Main lymphatic duct draining most of the body.
    MALT
    Mucosa-associated lymphoid tissue.
    Paratracheal Nodes
    Located lateral to the trachea.
    Lingual Tonsils
    Located at the base of the tongue.
    Central Axillary Nodes
    Located centrally in the armpit.
    Iliac Lymph Nodes
    Include external, internal, and common iliac nodes.
    Parotid Lymph Nodes
    Drain the lateral face and scalp.

    Red Bone Marrow

    Reviewed by our medical team

    Produces lymphocytes; site of B-cell maturation.

    1. Overview

    Red bone marrow is a vital soft tissue found within certain bones of the body, primarily responsible for hematopoiesis—the production of blood cells. It plays a dual role in both the circulatory and immune systems. Red bone marrow produces red blood cells, white blood cells (including lymphocytes), and platelets. As a primary lymphoid organ, it is crucial for the generation of B lymphocytes and the development of early-stage T lymphocyte precursors. Its role makes it indispensable in maintaining oxygen delivery, immune defense, and hemostasis.

    2. Location

    Red bone marrow is found within the trabecular (spongy) bone of specific skeletal regions. Its distribution changes with age:

    • In children: Found throughout most bones, including long bones (femur, humerus).

    • In adults: Restricted to the axial skeleton and proximal epiphyses of certain long bones.

    Major adult locations include:

    • Vertebrae

    • Sternum

    • Ribs

    • Iliac crests (hip bones)

    • Proximal femur and humerus

    With age, much of the red marrow in the appendicular skeleton is replaced by yellow marrow, composed mostly of adipose tissue.

    3. Structure

    Red bone marrow has a complex, supportive microenvironment suited for hematopoiesis and immune cell development. It consists of two major compartments:

    • Stroma: The connective tissue framework composed of:

      • Reticular cells and fibers

      • Adipocytes (fat cells)

      • Fibroblasts and endothelial cells

    • Hematopoietic compartment: Contains:

      • Hematopoietic stem cells (HSCs): Multipotent stem cells capable of producing all blood cell lines

      • Myeloid and lymphoid progenitor cells

      • Developing erythrocytes, leukocytes, and megakaryocytes

    Blood vessels in red marrow include sinusoids—thin-walled capillaries that allow mature blood cells to enter circulation directly.

    4. Function

    Red bone marrow performs several essential functions critical to both hematologic and immune system health:

    • Hematopoiesis: Generation of all blood cell types, including:

      • Red blood cells (erythrocytes)

      • White blood cells (leukocytes – granulocytes, monocytes, lymphocytes)

      • Platelets (via megakaryocytes)

    • Lymphopoiesis: Production of B lymphocytes and early T cell precursors (which then migrate to the thymus)

    • Storage of hematopoietic stem cells: Ensures a continuous supply of cells for blood renewal and repair

    5. Physiological Role(s)

    Red bone marrow contributes to a range of vital physiological processes:

    • Oxygen transport: Through the production of red blood cells containing hemoglobin

    • Immunity: As a primary lymphoid organ, it generates lymphocytes, including:

      • B cells: Mature within red marrow and later populate lymphoid organs

      • T cell precursors: Migrate to the thymus for further maturation

    • Coagulation: Produces platelets essential for blood clotting

    • Response to infection: Increases output of specific leukocytes in response to systemic infections

    • Tissue regeneration: Reservoir of multipotent stem cells capable of aiding in tissue repair and regeneration

    6. Clinical Significance

    Bone Marrow Disorders

    Disorders affecting red bone marrow can significantly impair immunity and blood cell production:

    • Aplastic anemia: Bone marrow fails to produce sufficient blood cells

    • Myelofibrosis: Replacement of marrow with fibrotic tissue, impairing function

    • Myelodysplastic syndromes: Ineffective hematopoiesis, often a precursor to leukemia

    Leukemia and Lymphoma

    Many hematologic cancers originate in or affect the red bone marrow:

    • Leukemia: Uncontrolled proliferation of abnormal white cells within the marrow

    • Multiple myeloma: Cancer of plasma cells derived from B lymphocytes

    Bone marrow biopsy is a key diagnostic tool for such diseases.

    Bone Marrow Transplantation

    Hematopoietic stem cell transplantation (commonly referred to as bone marrow transplant) is used to treat:

    • Leukemias and lymphomas

    • Aplastic anemia

    • Inherited immunodeficiencies

    Healthy stem cells are infused to repopulate and restore bone marrow function after chemotherapy or radiation.

    Marrow Suppression (Myelosuppression)

    This may occur due to:

    • Chemotherapy or radiation therapy

    • Certain infections (e.g., parvovirus B19)

    • Autoimmune disorders

    Consequences include pancytopenia, increasing the risk of infection, anemia, and bleeding.

    Imaging and Diagnostic Tests

    Assessment of red marrow includes:

    • Bone marrow aspiration and biopsy: For evaluation of marrow cellularity and morphology

    • Bone marrow MRI: Differentiates red marrow from yellow marrow and detects infiltration or malignancy

    Age-Related Changes

    With age, red bone marrow is progressively replaced by yellow marrow (fatty tissue), reducing hematopoietic activity. However, red marrow can reconvert in response to:

    • Severe anemia

    • High-altitude hypoxia

    • Chronic blood loss or increased hematopoietic demand

    Did you know? Lymphatic capillaries, the smallest of the lymphatic vessels, are extremely thin-walled and allow for the uptake of interstitial fluid.