Quiz 1

Organs of the Immune System

Primary Lymphoid Tissues

  • Definition: Sites where lymphocytes complete their development.

  • Key Organs:

    • Bone Marrow:

    • Produces B cells.

    • Thymus:

    • Site of T cell maturation.

Secondary Lymphoid Tissues

  • Definition: Locations where lymphocytes are stimulated and respond to pathogens, leading to clonal expansion.

  • Key Sites:

    • Lymph Nodes

    • Appendix

    • Spleen

    • Adenoids

    • Peyer's Patches in the small intestine

    • Tonsils

Lymphatic System Functionality

  • Plasma leaks from blood and is collected by lymphatic vessels, forming lymph.

  • Lymph is returned to the bloodstream via the thoracic duct into the subclavian vein.

  • The movement of lymph is primarily driven by body movement, assisted by one-way valves to prevent backflow.

  • Lymphatic fluid movement is typically slow.

George Syndrome

  • Definition: A genetic condition characterized by the absence of the thymus.

  • Consequence: Results in no T cell production and only a few antibodies produced, as B cells require T cells for optimal antibody (Ab) production.

  • Implications: Patients are immunodeficient and face a high risk of opportunistic infections.

  • Additional health issues: Heart defects and facial deformities commonly associated with this syndrome.

Lymph Nodes

  • Function: Sites where plasma leaks pick up pathogens and transport them via lymphatic capillaries.

  • Structure:

    • Afferent Lymphatic Vessels: Bring lymphatic fluid into the lymph node.

    • Efferent Lymphatic Vessels: Allow fluid to leave the lymph node.

  • Medulla: Functions as an "oil filter" for lymphatic fluid.

  • Inner Germinal Center:

    • Location where B cells divide and cluster, representing a dense population of lymphocytes in clonal expansion.

  • Outer Cortex: Contains increased lymphocyte proliferation due to infection.

Lymphadenopathy

  • Definition: Swollen lymph nodes resulting from increased lymphocyte proliferation (higher numbers of lymphocytes).

  • Occurs due to infection, leading to a larger block of clonal expanding lymphocytes rather than just fluid accumulation.

Inflammatory Reaction

  • Mechanism: Recruitment of white blood cells (WBCs) to sites of infection.

Spleen

  • Role: Critical for managing blood-borne infections (bacteremia).

  • Red Pulp:

    • Contains and removes old and damaged red blood cells (RBCs).

    • Macrophages within the red pulp phagocytize these cells.

  • White Pulp:

    • Functions as a secondary lymphoid tissue similar to lymph nodes, but without drainage.

    • Antigens enter through the artery directly.

Mucosa-associated Lymphoid Tissue (MALT)

  • Definition: Aggregations of lymphoid cells located in mucosal epithelia or in the lamina propria beneath mucosal tissue.

  • Associated with gut defense.

  • Types:

    1. Gut-associated Lymphoid Tissue (GALT): Includes tonsils, adenoids, appendix, and Peyer's patches.

    2. Bronchial-associated Lymphoid Tissue (BALT): Found in the respiratory tract.

Immune Response Mechanisms

  • Innate Immunity: Non-specific defense mechanisms present from birth.

  • Intracellular Pathogens: Not susceptible to soluble molecules (e.g., antibodies and complement).

  • Extracellular Pathogens: Susceptible to soluble molecules, which can target and neutralize them effectively.