Immune system

Cards (39)

  • Immune system
    Provides defense or immunity against infectious agents ranging from viruses to multicellular parasites
  • Immune system
    • Consists of a large, diverse population of leukocytes located within every tissue of the body and lymphoid organs interconnected only by the blood and lymphatic circulation
  • Two fundamental lines of defense
    • Innate immunity
    • Adaptive immunity
  • Innate immunity
    • Represents the first line of defense to an intruding pathogen
    • It is an antigen-independent (non-specific) defense mechanism that is used by the host immediately or within hours of encountering an antigen
  • Adaptive immunity
    • Acquired gradually by exposure to microorganisms
    • More specific
    • Develops more slowly and is based on antigen presentation to lymphocytes
    • Responses are aimed at specific microbial invaders and involve production of memory lymphocytes
  • Antigens
    Usually proteins that are recognized by lymphocytes to elicit a specific immune response against them
  • Antibodies
    Immunoglobulins produced by plasma cells after a progenitor B cell is activated by a specific antigen
  • Major Histocompatibility Complexes (MHC)

    • Cell surface glycoproteins whose primary function is to present peptide fragments for recognition by the appropriate T cells (lymphocytes)
    • MHC Class I Molecules are found on surfaces of all nucleated cells and bear fragments of their constituent proteins
    • MHC Class II Molecules are only found on antigen-presenting cells (APCs)
  • Two forms of adaptive immune response
    • Humoral immunity
    • Cell-mediated immunity
  • Cell-mediated immunity
    Mature T cells lymphocytes, macrophages, and the production of cytokines in response to an antigen are the main drivers
  • Primary Lymphoid Organs
    • Bone Marrow for B Lymphocytes
    • Thymus for T lymphocytes
  • Secondary Lymphoid Organs
    • Lymph Nodes
    • MALT
    • Spleen
  • Thymus
    • Bilobed organ in the mediastinum that is most active and prominent before puberty and undergoes involution with less activity in the adult
    • Found in the midline of the thoracic cavity, that is surrounded by the left and right pleural sacs
    • Primary organ where T Cells are produced
    • Originates from endoderm
  • Thymic Medulla
    • Contains fewer and larger, more mature lymphocytes
    • Cytoreticulum, supports T lymphocytes, dendritic cells and macrophages; expresses many specialized proteins specific to cells of other organs
    • Secondary Layer- serves as boundary between cortex and medulla
    • Hassall Corpuscles (Aggregates of TEC)
  • Mucosa-Associated Lymphoid Tissue (MALT)

    • Found in the mucosa of most tracts but is concentrated in the palatine, lingual and pharyngeal tonsils, Peyer patches, and the appendix
    • Collectively the MALT is one of the largest lymphoid organs, containing up to 70% of all the body's immune cells. Most of the lymphocytes here are B cells; among T cells, CD4+ helper T cells predominate
  • Lymph Nodes
    • Bean-shaped, encapsulated structures, generally only 10 mm by 2.5 cm in size, distributed throughout the body along the lymphatic vessels
    • Filters lymph
    • Site for B-cell activation and differentiation
  • Compartments of Lymph Nodes
    • Outer Cortex - point of entry of lymphocytes to the entire Lymph Node
    • Paracortex - High Endothelial Venules (HEVs) portal of entry of lymphocytes
    • Inner Medulla - Medullary Cords, Medullary Sinuses, Hilum - Where blood vessels and nerve(s) enter
  • Spleen
    • Only lymphoid organ involved in filtration of blood, making it an important organ in defense against blood-borne antigens
    • It is also the main site of old erythrocyte destruction
    • Without a cortex/medulla structure instead two intermingled but functionally different regions: white pulp and red pulp
  • Parts of the Red Pulp
    • Splenic Cords (Cords of Billroth) - contains macrophages, reticular cells and fibers, other leukocytes
    • Splenic Sinusoids - lined by unusual endothelial cells called stave cells that are elongated and aligned parallel to the blood flow
  • Innate immunity
    Involves leukocytes (mainly granulocytes), and proteins such as defensins, complement, lysozyme, and interferons; cytokines
  • Hydrochloric acid (HCI)

    Antimicrobial chemical
  • Defensins
    Short cationic polypeptides produced by neutrophils and various epithelial cells that kill bacteria by disrupting the cell walls
  • Lysozyme
    An enzyme made by neutrophils and cells of epithelial barriers, which hydrolyzes bacterial cell wall components, killing those cells
  • Complement
    A system of proteins in blood plasma, mucus, and macrophages that react with bacterial surface components to aid removal of bacteria
  • Interferons
    Paracrine factors from leukocytes and virus-infected cells that signal NK cells to kill such cells and adjacent cells to resist viral infection
  • Forms of adaptive immune response
    • Humoral immunity
    • Cell-mediated immunity
  • Humoral immunity
    • Antibodies are primarily responsible for the response
    • B cell lymphocytes, a type of immune cell that makes antibodies after detecting a specific antigen, are principally responsible for this method
  • Thymic Cortex
    • Darkly basophilic
    • Contains an extensive population of T lymphoblasts (or thymocytes) located among numerous macrophages and associated with the unique thymic epithelial cells (TECS) that have certain features of both epithelial and reticular cells
  • Squamous Cells
    • Blood-thymus barrier
  • Stellate Epithelial Cells
    • Cytoreticulum, secrete numerous cytokines for T-cell development
  • Squamous Cortical Cells
    • Corticomedullary barrier forms sheet like structure
  • Thymic Medulla
    Contains fewer and larger, more mature lymphocytes
  • Cytoreticulum
    • Supports T lymphocytes, dendritic cells and macrophages; expresses many specialized proteins specific to cells of other organs
  • Secondary Layer
    • Serves as boundary between cortex and medulla
  • Hassall Corpuscles
    • Aggregates of TEC
  • Thymic Cortex
    • Darkly basophilic
    • Contains an extensive population of T lymphoblasts (or thymocytes) located among numerous macrophages and associated with the unique thymic epithelial cells (TECS) that have certain features of both epithelial and reticular cells
  • Thymic Cortex Cell Types
    • Squamous Cells - Blood-thymus barrier
    • Stellate Epithelial Cells - Cytoreticulum, secrete numerous cytokines for T-cell development
    • Squamous Cortical Cells - Corticomedullary barrier forms sheet like structure
  • Thymic Medulla
    • Contains fewer and larger, more mature lymphocytes
  • Thymic Medulla Components
    • Cytoreticulum, supports T lymphocytes, dendritic cells and macrophages; expresses many specialized proteins specific to cells of other organs
    • Secondary Layer - serves as boundary between cortex and medulla
    • Hassall Corpuscles (Aggregates of TEC)