JE

AnaPhy-The-Lymphatic-System

The Lymphatic System Overview

  • The lymphatic system supports the cardiovascular system and is crucial for immune function.

  • It consists of:

    • A network of lymphatic vessels.

    • Various lymphoid tissues and organs throughout the body.

  • Functions include transporting escaped fluids back to the cardiovascular system and housing immune components like phagocytic cells and lymphocytes.

Lymphatic Vessels

  • Blood circulation processes result in approximately 3 L of excess fluid remaining in tissue spaces each day.

  • Lymphatic vessels collect this excess interstitial fluid, referred to as lymph, and return it to the bloodstream.

  • Lymph capillaries feature highly permeable walls with flaplike mini-valves that:

    • Open to allow fluid entry when interstitial pressure is high.

    • Close to prevent backflow when pressure inside vessels rises.

Flow of Lymph

  • Lymph flows from capillaries through lymphatic vessels to:

    • The right lymphatic duct (draining the right arm and right side of the head/thorax).

    • The thoracic duct (draining the rest of the body).

  • Both ducts empty lymph into the subclavian vein.

Lymph Node Functions

  • Lymph nodes filter lymph, removing foreign materials and producing lymphocytes.

  • They are distributed throughout the body, particularly in clustered regions (inguinal, axillary, cervical).

  • Swelling of lymph nodes during infections indicates immune activity and is commonly known as "swollen glands."

Structure of Lymph Nodes

  • Kidney-shaped, ~1 cm long, surrounded by a fibrous capsule with internal trabeculae dividing compartments.

  • Cortex contains lymphocyte collections (follicles) that enlarge during immune responses (B cells).

  • Structure includes:

    • Afferent and efferent lymphatic vessels.

    • Macrophages that destroy pathogens.

Other Lymphoid Organs

  • Include:

    • Spleen: Filters blood and destroys worn-out red blood cells, also a blood reservoir.

    • Thymus: Site of T cell maturation, primarily active during childhood.

    • Tonsils: Trap and remove pathogens in the pharynx.

    • Peyer’s Patches and Appendix: Prevent intestinal infections.

Body Defense Mechanisms

  • The immune system features innate (nonspecific) and adaptive (specific) responses.

  • Innate Defense: Responds immediately to all foreign substances (skin, mucous membranes, phagocytes).

  • Adaptive Defense: Tailored against specific pathogens, involves B and T lymphocytes, develops immunity post-exposure.

Distinguishing Immune Responses

  • Adaptive Response's Features: Includes specificity, systemic nature, and memory after antigen exposure.

  • Humoral Immunity: Antibodies in body fluids.

  • Cellular Immunity: Lymphocytes defending against infected or cancerous cells.

Antigens and Immune Responses

  • Antigens: Substances stimulating immune responses (foreign proteins, bacteria).

  • Self vs. Nonself Antigens: Self-antigens prevent immune response; nonself can provoke it (e.g., transplants may trigger rejection).

Types of T and B Lymphocytes

  • B Cells: Produce antibodies; oversee humoral immunity.

  • T Cells: Directly eliminate infected or cancerous cells; include helper and cytotoxic types.

  • APCs (Antigen-Presenting Cells): Activate T cells for immune responses.

Immune System Regulation

  • Cytokines: Enhance immune responses by attracting immune cells and stimulating lymphocyte proliferation.

  • Memory Cells: Provide long-lasting immunity for quicker responses to future exposures.

Immunodeficiencies and Autoimmunity

  • Immunodeficiencies: Can be congenital or acquired (AIDS); lead to high susceptibility to infections.

  • Autoimmune Diseases: The immune system attacks the body's own cells due to mistaken identity of self-antigens.

Treatment and Management

  • Immunosuppressive therapies are often necessary for managing autoimmunity or preventing transplant rejection. Ongoing research aims for better tolerance.

Developmental Aspects of the Lymphatic System

  • Lymphatic vessels arise from embryonic veins around the fifth week of gestation, developing key functions for fluid balance and immunity.

  • Postnatal development includes rapid lymphocyte population growth, essential for robust immune function.