Lymph Transport & Immunity

Lymph Transport & Immunity

The Lymphatic System

• Components:

  • Lymphatic vessels

  • Lymphoid organs

• Functions:

  • Homeostatic Functions:

  • Lymphatic capillaries:

    • Take up excess fluid not reabsorbed by blood capillaries and return it to the bloodstream.

  • Lacteals:

    • Specialized lymphatic capillaries in the intestines, transport lipoproteins to the bloodstream.

  • Responsible for immune defense through cells, tissues, and organs.

  • Lymphocytes:

    • Respond to:

    • Invading pathogens: Such as bacteria or viruses.

    • Abnormal body cells: Such as cancer cells.

    • Foreign proteins: Such as toxins.

Anatomy of the Lymphatic System

• Structures Involved:

  • Adenoids

  • Tonsils

  • Lymph nodes

  • Mass amounts of lymphocytes and macrophages present.

  • Peyer’s patches: Located in small intestine.

  • Spleen

  • Appendix

  • Lymphatic vessels

  • Blood capillaries

  • Lymphatic capillaries:

  • Begin the one-way flow of lymph from interstitial fluid to larger vessels.

Lymphatic System Mechanics

• Flow Direction:

  • One-way system beginning with lymphatic capillaries.

  • Fluid flows from small capillaries to larger lymphatic vessels and finally to a lymphatic duct that empties into a subclavian vein.

• Edema:

  • Definition: Localized swelling resulting from excess tissue fluid accumulation.

Lymphatic Organs

1. Red Bone Marrow:

   • Origin of all blood cell types and maturation site for B lymphocytes.

2. Thymus Gland:

   • Located along the trachea, behind the sternum; responsible for T lymphocyte maturation.

3. Spleen:

   • Located in the upper left of the abdominal cavity, cleanses blood.

4. Lymph Nodes:

   • Surrounded by a capsule; consist of two regions: cortex and medulla.

     • Cortex: Contains lymphocytes that respond to pathogens.

     • Medulla: Contains macrophages that cleanse lymph.

5. Tonsils:

   • Patches of lymphatic tissue near the pharynx; first line of defense against inhaled or ingested pathogens.

The Immune System

• Function: Defense against dangerous pathogens.

• Two Major Defense Types:

  • Innate Immunity (Non-Specific):

  • Broad and quick; reacts to various threats in a general manner.

  • Types include:

    • Physical barriers: Skin and mucous membranes.

    • Inflammation: Localized response causing redness, swelling, and pain.

    • Complement system: Proteins that enhance immune responses.

    • Fever: Increase in body temperature.

    • Phagocytes: Cells that engulf pathogens.

    • Immunological surveillance: Monitoring for abnormal cells.

    • Interferons: Proteins released by virus-infected cells.

  • Acquired Immunity (Specific):

  • Highly specific to particular pathogens.

  • Takes 5-7 days to develop.

  • Types:

    • Humoral Response: Mediated by B-lymphocytes producing antibodies.

    • Cell-mediated Response: Involves cytotoxic T-lymphocytes.

Nonspecific Defenses

• Physical Barriers:

  • Mechanical barriers include hair and epithelial secretions.

  • Mucous membranes line tracts, trapping and sweeping microbes.

• Inflammatory Reaction:

  • Response to tissue injury.

  • Histamines and kinins released from damage lead to capillary dilation.

  • Results in:

  • Temporary repair of injury.

  • Slowed pathogen spread.

  • Mobilization of immune responses.

  • Neutrophils and monocytes migrate to the area, phagocytizing pathogens.

• Complement System:

  • Composed of plasma proteins; acts after pathogen entry, causing cell destruction via membrane attack complexes.

• Fever:

  • Maintains body temperature above 37.2°C (99°F).

  • Pyrogens reset hypothalamic thermostat, providing a hostile environment for pathogens.

• Phagocytes and Natural Killer (NK) Cells:

  • Recognize abnormal proteins, secrete perforins to destroy infected cells.

• Interferons:

  • Released by infected cells to trigger anti-viral responses in neighboring cells.

Cell-Mediated Immunity

• Mechanism involves cytotoxic T cells; release perforins and granzymes to induce apoptosis in infected target cells.

Adaptive (Acquired) Immunity

• Initiated by exposure to antigens, involves specific immune responses.

• Clonal Selection Theory:

  • Antigen selects which lymphocyte undergoes clonal expansion.

  • Memory B cells respond rapidly upon secondary exposure to the same antigen.

Forms of Immunity

1. Innate Immunity:

   • Genetically determined, present at birth.

2. Acquired Immunity:

   • Not present at birth, developed through exposure to antigens.

   • Types include:

     • Active Immunity: Develops via vaccinations.

     • Passive Immunity: Transfer of antibodies, e.g., from mother to child.

Immunoglobins (Antibodies)

• Types:

  • IgG: Main circulating antibody.

  • IgM: Largest antibody, present in circulation.

  • IgA: Found in secretions.

  • IgD: Present on immature B cells.

  • IgE: Involved in allergic responses.

Monoclonal Antibodies

• Produced against a specific antigen using hybridomas, which are fused B cells and myeloma cells.

• Medical Uses:

  • Diagnostic testing and treatments, e.g., pregnancy tests.

T Cells

• Recognition Requirements:

  • Antigen must be presented by antigen-presenting cells linked to MHC proteins.

• Types of T Cells:

  • Cytotoxic T Cells: Destroy infected or abnormal cells.

  • Helper T Cells: Activate other immune cells and regulate immunity via cytokines.

  • Suppressor T Cells: Inhibit activity of T and B cells.

HIV Infections

• HIV primarily targets helper T cells, causing their destruction and leading to immune system failure over time.

Cytokines and Immunity

• Cytokines: Signaling molecules that enhance immune responses.

• Types:

  • Interleukins: Stimulate immune cells.

  • Tumor Necrosis Factor (TNF): Induces cancer cell death.

Immunity Side Effects

• Tissue Rejection: Resulting from immune response to foreign tissues.

• Autoimmune Diseases: Immune system erroneously attacks the body's own cells, e.g., rheumatoid arthritis.

• Allergies: Hypersensitivity reactions; triggered by IgE antibodies in immediate responses or memory T cells in delayed responses.