Lymphatic

Lymphatic System and Body Defenses

1. Lymphatic System

• Functions: Returns excess fluid to blood; protects against disease.

• Lymph: Excess tissue fluid.

• Edema: Fluid buildup in tissues.

• Lymphatic vessels: Carry lymph toward the heart.

• Right lymphatic duct: Drains right upper body.

• Thoracic duct: Drains the rest of the body.

2. Lymph Nodes and Organs

• Lymph nodes: Filter lymph.

• Macrophages: Engulf pathogens.

• Lymphocytes: Fight foreign substances.

• Cortex: Outer region; lymphocyte follicles.

• Medulla: Inner region.

• Spleen: Filters blood; destroys old blood cells.

• Thymus: T-cell maturation; most active during youth.

• Tonsils: Trap pathogens in the throat.

• Peyer’s patches: Protect the small intestine.

• MALT: Protects respiratory and digestive tracts.

3. Three Lines of Defense

• First line: Skin, mucus, secretions.

• Second line: Phagocytes, NK cells, inflammation, fever, antimicrobial proteins.

• Third line: B cells, T cells, antibodies.

4. Innate Immunity

• Innate: Nonspecific, immediate defense.

• Mucus: Traps pathogens.

• Lysozyme: Destroys bacteria.

• NK cells: Kill infected and cancer cells.

• Phagocytosis: Engulfing and digesting pathogens.

• Inflammation: Redness, heat, pain, swelling.

• Histamine: Causes vasodilation and increased capillary leakage.

• Diapedesis: WBCs pass through capillary walls.

• Chemotaxis: WBCs move toward infection.

• Complement: Helps destroy pathogens.

• MAC: Forms pores in target cells, causing lysis.

• Interferons: Inhibit viral multiplication.

• Fever: Helps fight infection.

5. Adaptive Immunity

• Adaptive: Specific defense with memory.

• Antigen: Triggers an immune response.

• B cells: Mature in bone marrow; produce antibodies through plasma cells.

• T cells: Mature in thymus; attack infected cells.

• APCs: Present antigens to T cells.

• Memory cells: Provide faster responses to repeated infections.

6. Humoral vs. Cellular Immunity

• Humoral: B cells and antibodies; extracellular pathogens.

• Cellular: T cells; infected and cancer cells.

• Plasma cells: Produce antibodies.

• Helper T cells: Activate immune cells.

• Cytotoxic T cells: Kill infected cells.

• Regulatory T cells: Suppress immune responses.

• Cytokines: Immune cell messengers.

7. Antibody Classes — MADGE

• IgM: Activates complement.

• IgA: Secretions, mucus, tears.

• IgD: B-cell activation.

• IgG: Most abundant in plasma; crosses placenta.

• IgE: Allergies.

Antibody actions

• Neutralization: Blocks toxins or viruses.

• Agglutination: Clumps antigens.

• Precipitation: Makes soluble antigen complexes settle.

• Complement fixation: Activates complement proteins.

8. Types of Immunity

• Active: Body produces its own antibodies.

  • Natural: Infection.

  • Artificial: Vaccine.

• Passive: Receives antibodies.

  • Natural: Mother to baby.

  • Artificial: Donated antibodies.

• Key difference: Passive immunity has no memory and is temporary.

9. Disorders of Immunity

• Allergy: Overreaction to harmless antigens.

• Anaphylaxis: Severe systemic allergic reaction.

• Autoimmunity: Attacks the body’s own tissues.

• Immunodeficiency: Weak or abnormal immune function.

• SCID: Congenital immunodeficiency.

• AIDS: HIV attacks helper T cells.

Examples of autoimmune diseases

• Rheumatoid arthritis — joints.

• Myasthenia gravis — nerve-muscle communication.

• Multiple sclerosis — brain and spinal cord white matter.

• Graves’ disease — excess thyroid hormone.

• Type I diabetes — pancreatic beta cells.

• SLE — multiple organs.

• Glomerulonephritis — kidney inflammation.

10. Organ Transplants

• Autograft: Same person.

• Isograft: Genetically identical person.

• Allograft: Another person.

• Xenograft: Different species.

• Immunosuppressants: Help prevent rejection.

11. Development

• Lymphatic vessels develop from veins.

• Thymus and spleen are the first lymphoid organs to appear in the embryo.

• Immune response develops around birth.

• Aging decreases immune efficiency.