Lymphatic System and Lymph Drainage

Lymphatic System and Immunity

Functions of the Lymphatic System

  1. Fluid balance: Helps maintain fluid levels in the body.

  2. Fat absorption: Assists in the absorption of fats and fat-soluble vitamins.

  3. Defense: Plays a critical role in the immune response.

Components of the Lymphatic System

  • Lymph: Fluid containing water and solutes that enters lymphatic capillaries.

  • Lymphocytes: A type of immune cell that is made in the bone marrow and is found in the blood and in lymph tissues.

  • Lymphatic vessels: A thin tube that collects lymph (clear watery fluid) from tissues in different parts of the body and returns it to the bloodstream.

  • Lymph nodes: Filter lymph and activate immune responses.

  • Tonsils: Guard against pathogens entering through the mouth and nose.

  • Spleen: Filters blood, removes old cells, and mounts immune responses.

  • Thymus gland: Site of T lymphocyte maturation.

Lymphatic Capillaries

  • Structure: Tiny, closed-ended vessels that allow fluid movement from tissues.

  • Function: Carries lymph in one direction towards the circulatory system and joins to form larger lymphatic vessels.

Lymphatic Vessels

  • Structure: Resemble small veins and have one-way valves.

  • Right lymphatic duct: Drains lymph from the upper right side of the body into the right subclavian vein.

  • Thoracic duct: Drains lymph from the rest of the body into the left subclavian vein.

Lymphatic Organs

Tonsils

  • Types:

    • Palatine tonsils: On each side of the oral cavity.

    • Pharyngeal tonsils: Near the internal opening of the nasal cavity (adenoid).

    • Lingual tonsils: Located on the posterior surface of the tongue.

  • Function: Form a protective ring of lymphatic tissue around the nasal and oral cavities.

Lymph Nodes

  • Structure: Rounded structures located near lymphatic vessels (in groin, armpit, neck).

  • Function: Filter lymph, activate lymphocytes if foreign substances are detected, and remove microbes.

Spleen

  • Size: Approximately the size of a clenched fist, located in the abdomen.

  • Function: Filters blood, responds to foreign substances, destroys old red blood cells, and serves as a blood reservoir.

  • Types of pulp:

    • White pulp: Lymphatic tissue surrounding arteries.

    • Red pulp: Contains macrophages and red blood cells that connect to veins.

Thymus Gland

  • Structure: Bilobed gland located in the mediastinum behind the sternum.

  • Growth: Stops growing at age 1, decreases in size by age 60.

  • Function: Produces and matures T lymphocytes.

Immunity

  • Definition: Ability to resist damage from foreign substances, microbes, toxins, and cancer cells.

  • Types:

    • Innate Immunity: Present at birth; defends against any pathogen.

    • Adaptive Immunity: Acquired after birth; specific response to specific antigens.

Innate Immunity

  • Characteristics:

    • Physical barriers: Skin and mucous membranes.

    • Chemical mediators: Lysozyme (kills bacteria), histamine (promotes inflammation).

  • Cells involved: White blood cells such as neutrophils and macrophages.

Adaptive Immunity

  • Definition: Specific recognition to specific antigens that involves lymphocytes (B and T cells).

  • Types:

    • Antibody-mediated immunity: B cells produce antibodies.

    • Cell-mediated immunity: T cells destroy pathogen-infected cells.

Lymphocytes

  • Types:

    • B cells: Mature in red bone marrow, involved in antibody production.

    • T cells: Mature in thymus; include Helper T cells (activate immune response) and Cytotoxic T cells (destroy infected cells).

Antibodies

  • Structure: Y-shaped proteins with variable and constant regions.

  • Classes of Immunoglobulins:

    • IgG: 80 to 85% in serum. Activates compliment and increases phagocytosis. Main antibody; can cross placenta. Responsible for Rh reactions, such as hemolytic disease of

    • IgM: First antibody produced in response.

    • IgA: Found in secretions (saliva, tears).

    • IgE: Involved in allergic responses.

    • IgD: Functions as an antigen receptor on B cells.

Antibody Production

  • Primary Response: First exposure leads to B cell activation and antibody production which may take 3-14 days.

  • Secondary Response: Occurs upon re-exposure with a faster response due to memory cells.

Cell-Mediated Immunity

  • Attacks: Effective against intracellular pathogens (bacteria, viruses).

  • T cell Roles:

    • Helper T cells activate others.

    • Cytotoxic T lymphocytes (CTL) directly destroy infected cells.

    • Regulatory T cells control immune response.

Types of Adaptive Immunity

Naturally Acquired Immunity

  • Active: Natural exposure results in antibody production.

  • Passive: Antibodies transferred from mother to child.

Artificially Acquired Immunity

  • Active: Vaccination induces antibody formation.

  • Passive: Direct injection of antibodies from another source.