LYMPHOID

• Lymphoid System


  A complex network of ducts, nodes and other organs that are located throughout the body
• Lymphoid System


  • First line of defense
  • Inflammatory response
  • Immune response
• Physical Barriers


  • Skin
  • Mucus Membranes (mucosae)
• Skin cannot normally be penetrated by bacteria and viruses
• Secretions from sebaceous and sweat glands keep the skin in a pH range of 3 to 5 (acidic)
• Microbial colonization is also inhibited by saliva, tears, and mucus secretions that continually bathe exposed epithelium
• All of these secretions contain antimicrobial proteins, an example is lysozyme, an enzyme that digests the cell walls of many bacteria
• Mucus Membranes (mucosae) line digestive, respiratory, and genitourinary tracts and also prevent entry of harmful microbes
• In the trachea, ciliated epithelial cells sweep out mucus and trapped microbes
• Inflammatory Response


  Tissue damages leads to a localized inflammatory response (nonimmune response; inflammation)
• Inflammatory Response


  • Increased dilation
  • Increased permeability
  • Leads to increased redness, heat, and swelling
• Effector Cells


  • Neutrophils
  • Macrophages
  • Eosinophils
  • Basophils
  • Mast cells
  • NK cells
  • T cells
• Phagocytes


  Rapid response to invasion
• Neutrophils are the first phagocytes to arrive, followed by macrophages that consume pathogens and their products, as well as damaged tissue cells and the remains of neutrophils
• The dead phagocytic cells and fluids leaked from capillaries is called pus
• Complement System


  A collection of more than 20 plasma proteins that produced by the liver, which enhances phagocytosis and involved in both inflammatory and immune response
• Activation of the Complement System

  • Production of chemotaxins
  • Marking off bacteria with proteins (opsonins)
  • Facilitate phagocytosis
  • Release of cytokines
  • Release of histamine which is secreted by mast cells and basophils
• Histamine Release


  Inflammation sets off histamine release by basophils and mast cells, which triggers increased dilation and permeability of nearby capillaries
• Damaged tissues also release prostaglandins and other substances that promote blood flow to the injured site, enhancing delivery of clotting elements, blocking spread of microbes, and enhancing migration of phagocytic cells
• Systemic Response


  If damage or infection is severe, a widespread non-specific response may occur, including an increase in the number of leukocytes in the blood several-fold within a few hours
• Lymphoid System


  A complex network of ducts, nodes and other organs that are located throughout the body
• Fever


  A systemic response characterized by increased body temperature, which may be triggered by toxins or by pyrogens released from leukocytes, and which inhibits growth of some microbes, facilitates phagocytosis, and speeds up repair of tissue
• Lymphoid System


  • First line of defense
  • Inflammatory response
  • Immune response
• Immune Response (Immunological Response)

  A more powerful body defense system than the inflammatory response, which is antigen-specific and must be developed for every antigen that the body encounters for the first time
• Physical Barriers


  • Skin
  • Mucus Membranes (mucosae)
• Antigen


  Any substance that the immune system perceives as foreign to the body and which, consequently, induces an immune response
• Skin cannot normally be penetrated by bacteria and viruses
• Lymphocytes


  The principal effector cells of the immune response
• Secretions from sebaceous and sweat glands keep the skin in a pH range of 3 to 5 (acidic)
• Types of Immune Responses

  • Humoral Immunity (Antibody-Mediated Immunity)
  • Cell-Mediated Immunity (CMI)
• Microbial colonization is also inhibited by saliva, tears, and mucus secretions that continually bathe exposed epithelium
• Humoral Immunity


  Immunity mediated by antibodies (immunoglobulins) synthesized by plasma cells, important in containing many viral and bacterial infections, and also conferred by vaccines
• All of these secretions contain antimicrobial proteins, e.g. lysozyme, an enzyme that digests the cell walls of many bacteria
• Cell-Mediated Immunity (CMI)


  Immunity not mediated by antibodies, plays a major role in conferring immunity to microorganisms that are located intercellularly and therefore protected from antibodies, also responsible for delayed hypersensitivity reaction, and tissue and organ transplant rejection
• Effector Cells


  • Cytotoxic T Cells
  • Macrophages
• Mucus Membranes (mucosae) line digestive, respiratory, and genitourinary tracts and prevent entry of harmful microbes
• Cytotoxic T Cells


  Target virus-infected cells, cells with intracellular bacteria and cancer cells, and induce apoptosis of the target cell by releasing proteins into the target cell
• In the trachea, ciliated epithelial cells sweep out mucus and trapped microbes
• Apoptosis


  A form of cell death in which a programmed sequence of events leads to the elimination of cells without releasing harmful substances into the surrounding area
• Inflammatory Response


  Tissue damages leads to a localized inflammatory response (nonimmune response; inflammation)