11. LYMPHATIC SYSTEM

Introduction

The lymphatic system is an accessory drainage system closely linked with the venous system. It absorbs excess tissue fluid, removes large particles like proteins, and plays a vital role in immunity.

LYMPH AND LYMPHATIC SYSTEM

  • Lymphatic system absorbs 10–20% of tissue fluid not reabsorbed by venous capillaries.
  • Removes larger particles such as proteins and particulate matter.
  • Lymph flows through lymph nodes before draining into venous blood.
  • Lymph from intestines, called chyle, is milky due to fat absorption via lacteals.

FUNCTIONS OF THE LYMPHATIC SYSTEM

  1. Drains excess interstitial fluid – Maintains circulating blood volume.
  2. Transports dietary lipids – Fat-soluble vitamins (A, D, E, K).
  3. Carries out immune responses – Lymphoid tissue responds to microbes or abnormal cells.

COMPOSITION, FORMATION AND CIRCULATION

Components of the lymphatic system

  1. Lymph vessels
    • Begin blindly in tissue spaces; form intricate networks.
    • Larger, more permeable than blood capillaries.
    • Join to form superficial and deep lymphatics, passing through lymph nodes.
    • Drain into thoracic duct and right lymphatic duct.
  2. Central lymphoid tissues
    • Bone marrow and thymus.
    • Bone marrow: Differentiates B-lymphocytes → plasma cells.
    • Thymus: Differentiates T-lymphocytes → immune defense.
  3. Peripheral lymphoid organs
    • Lymph nodes, spleen, and epithelial-lymphoid tissues.
    • Sites for lymphocyte proliferation and maturation.
  4. Circulating pool of lymphocytes
    • Mature B- and T-lymphocytes ready to respond to antigens.

LYMPHATIC FOLLICLE

  • Spherical collection of lymphocytes; germinal center is the less dense, actively dividing region.

LYMPH NODES

  • Small nodules along lymph vessels; filter lymph before draining into larger trunks.
  • Structural components:
    1. Fibrous and reticular framework – Capsule and trabeculae.
    2. Lymphatic channels – Subcapsular sinus → efferent lymphatic.
    3. Cortex – Zones 1–3; outer: B-lymphocytes, inner/paracortex: T-lymphocytes.
    4. Medulla – Loosely packed lymphocytes, plasma cells, macrophages.
    5. Blood channels – Arteries, capillaries, venules supporting lymphocyte migration.
  • Haemal nodes – Lymph-node-like structures filled with blood, not lymph; intermediate between lymph node and spleen.

MONONUCLEAR PHAGOCYTE SYSTEM

  • Also called the macrophage system, distributed widely throughout the body.
  • Components:
    a) Macrophages in connective and reticular tissue, lungs
    b) Monocytes in blood
    c) Kupffer cells of liver
    d) Meningocytes of meninges
    e) Microglial cells in nervous tissue
    f) Foreign body giant cells
  • Functions:
    1. First line of defense against microorganisms.
    2. Plays a role in specific immune responses in lymphoid tissue.
    3. Sites also participate in haemopoiesis.

Detailed Notes:

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