Lymphatic and Immune Systems Review//STUDIED

Lymphatic System and Immunity

Organization of the Lymphatic System

• Anatomy of the Lymphatic System

  • Lymph: Fluid similar to plasma but lacks plasma proteins.
  • Lymphatic Vessels (Lymphatics): Network carrying lymph from peripheral tissues to the venous system.
  • Lymphoid Tissues and Lymphoid Organs: Includes tonsils, lymph nodes, thymus, spleen, etc.
  • Immune System Cells: White blood cells (WBCs).

• Function of the Lymphatic System

  • Produces, maintains, and distributes lymphocytes.

• Lymphatic Vessels

  • Lymphatic Capillaries: Smallest vessels, starting as blind sacs where interstitial fluid diffuses in.
    • Large diameter, thin-walled.
    • Cells act as one-way valves, allowing fluid in but not out.
  • Lymphatic vessels travel along the same pathways as veins; divided into deep and superficial lymphatics.
  • Larger lymphatic vessels contain valves to prevent backflow.
  • Main Lymphatic Vessels
    • Thoracic Duct: Receives lymph from the lower body and left side of the upper body; drains into the left subclavian vein.
    • Right Lymphatic Duct: Receives lymph from the right side of the upper body and head; drains into the right subclavian vein.

• Lymphocytes

  • Classes of Circulating Lymphocytes:
    • T-cells (Thymus-dependent)
      • Cytotoxic T-cells: Mediate cell-mediated immunity; attack virus-infected cells.
      • Helper T-cells: Stimulate T-cell and B-cell function.
      • Suppressor T-cells: Inhibit T-cell and B-cell function.
    • B-cells (Bone Marrow-derived)
      • Differentiate into plasma cells, which secrete antibodies (immunoglobulins); mediate antibody-mediated immunity.
    • NK Cells (Natural Killer Cells)
      • Responsible for immune surveillance.
  • Life Span and Circulation of Lymphocytes
    • Can survive for many years.
    • Travel throughout the bloodstream, migrate through tissues, and return to the circulatory or lymphatic system.
  • Lymphocyte Production
    • Two types of lymphoid stem cells:
      • In red bone marrow: gives rise to B-cells and NK cells.
      • In the thymus: gives rise to T-cells; isolated from general circulation during development by the blood-thymus barrier.
        • Thymosins (thymus hormones) alter T-cells.

• Lymphoid Tissues

  • Concentrations of lymphocytes within other body tissues.
  • Example: Lymphoid nodules in the wall of the intestines called Peyer’s patches or MALT.
  • Another example: Tonsils.

• Lymphoid Organs

  • Lymph Nodes: Lymphatic vessels carry lymph to lymph nodes for filtration and then away to the venous system.
    • Contain T-cells, B-cells, and macrophages which remove debris, pathogens, and antigens.
    • Clustered in specific areas to prevent the spread of infection (e.g., axillary, inguinal lymph nodes).
  • Thymus: Located in the mediastinum; deteriorates after puberty.
    • Has two lobes.
    • Secretes thymosins, important for T-cell maturation.
  • Spleen
    • Anatomy
      • Red Pulp: Contains large numbers of RBCs.
      • White Pulp: Resembles lymphoid nodules.
    • Functions
      • Removes abnormal blood cells and other blood components via phagocytosis.
      • Stores iron recycled from RBCs.
      • Initiates immune response by T-cells and B-cells to circulating antigens in the blood.
    • Splenectomy: Surgical removal of the spleen.
      • Increases susceptibility to pneumococcal infections.
      • Pneumococcal vaccination is recommended post-splenectomy.

  *NOTE: Lymphoid tissues and organs contain both T and B cells; organs have fibrous outer capsules and are more organized in their internal structure.

Lymphatic System and Body Defenses

• Non-Specific Defenses (Innate Immunity)

  • Attacks all invaders in the same way.
  • Physical and Chemical Barriers
    • Skin
    • Hair
    • Epithelial layers of internal passageways
    • Secretions that flush away materials (sweat glands, mucus)
    • Secretions that kill or inhibit microorganisms (enzymes, stomach acid).
  • Phagocytes
    • Microphages: Neutrophils and eosinophils.
    • Macrophages
      • Fixed Macrophages: Stay in specific tissues or organs.
      • Free Macrophages: Travel through the body.
    • Microphages and free macrophages respond to chemotactic signals; all can leave the bloodstream and enter tissues.
  • Immunological Surveillance: Constant monitoring of normal tissues by NK cells.
    • NK cells attack abnormal cells anywhere in the body, including cancer cells and virus-infected cells.
  • Interferons: Proteins that signal the presence of viruses and stimulate cells to produce antiviral proteins, which block viral replication.
  • Complement: A group of proteins that complements the action of antibodies.
    • Activation of complement:
      • Stimulation of inflammation.
      • Attraction of phagocytes.
      • Enhancement of phagocytosis through opsonization (antibodies coat antigens).
      • Destruction of target cell membranes via membrane attack complex (MAC). MAC involves 5 complement proteins that punch holes in the cell membrane.
  • Inflammation: Localized response to injury.
    • Signs of Inflammation
      • Swelling: Accumulation of excess fluid in interstitial spaces.
      • Redness: Increased blood flow (vasodilation).
      • Heat: Increased blood flow.
      • Pain: Distortion/destruction of cell membranes.
    • Necrosis: Local tissue destruction in the area of injury.
    • Pus: Debris and necrotic tissue, including dead WBCs.
    • Abscess: Pus accumulation in an enclosed space.
  • Fever: Maintained body temperature above 99° F.
    • Pyrogens: Substances that cause fever.
    • Endogenous Pyrogen: Released by macrophages.

• Specific Defenses (Adaptive Immunity)

  • General
    • Designed to attack only the invader for which it is programmed, ignoring all others.
    • Relies on the action of specific lymphocytes – T-cells and B-cells.
  • Forms of Immunity
    • Innate: Present at birth; non-specific immunity.
    • Acquired: Appears after birth upon exposure to an antigen.
      • Active: The person has been exposed to the antigen, and their body actively makes antibodies against it.
        • Naturally acquired: exposure to the disease itself.
        • Artificially acquired: immunization.
      • Passive: A person is given antibodies manufactured by another organism.
        • The person's immune system never sees the antigen and cannot produce antibodies.
        • Naturally acquired: Antibodies received through mother’s milk or across the placenta.
        • Artificially acquired: Receiving hepatitis A immunoglobulin to prevent infection.

Properties of Immunity

• Specificity: Each T or B-cell responds only to one antigen, based on its molecular structure, and ignores all others.
• Versatility: The body produces a small number of many differently coded lymphocytes (T-cells and B-cells), so the immune system can fight many different types of antigens.
  • Once a lymphocyte has been