🫁Honors Anatomy and Physiology Unit 11 – Lymphatic & Immune Systems

Key Components and Structure

• Lymphatic vessels transport lymph throughout the body
  • Lymph consists of fluid, proteins, lipids, and white blood cells (lymphocytes)
  • Lymphatic capillaries absorb excess interstitial fluid and return it to the bloodstream
• Lymph nodes filter lymph and trap pathogens and foreign substances
  • Lymph nodes contain concentrations of lymphocytes and macrophages
  • Lymph nodes are located in clusters throughout the body (axillary, inguinal, cervical)
• Lymphoid organs include the spleen, thymus, tonsils, and Peyer's patches
  • The spleen filters blood, removes old red blood cells, and stores platelets
  • The thymus is the site of T-lymphocyte maturation and development
• Lymphoid tissues are found in mucous membranes (MALT) and skin (SALT)
  • MALT includes the tonsils, adenoids, and Peyer's patches in the small intestine
  • SALT is found in the dermis and provides a barrier against pathogens
• Lymphocytes are the primary cells of the lymphatic system
  • B-lymphocytes produce antibodies and are involved in humoral immunity
  • T-lymphocytes are involved in cell-mediated immunity and include helper T cells, cytotoxic T cells, and regulatory T cells

Functions of the Lymphatic System

• Maintains fluid balance by returning excess interstitial fluid to the bloodstream
  • Prevents edema, the accumulation of excess fluid in tissues
• Absorbs and transports dietary lipids from the small intestine to the bloodstream
  • Lacteals in intestinal villi absorb chylomicrons, lipoproteins containing dietary lipids
• Provides a pathway for the circulation of lymphocytes and other immune cells
  • Enables immune cells to patrol the body and respond to pathogens and foreign substances
• Filters lymph and removes pathogens, debris, and abnormal cells
  • Lymph nodes trap and destroy pathogens and cancer cells
• Participates in the immune response by producing and activating lymphocytes
  • Lymphoid organs and tissues are sites of lymphocyte development and activation
• Aids in the removal of cellular waste products and dead cells
  • Macrophages in lymph nodes phagocytose debris and apoptotic cells

Immune System Basics

• The immune system protects the body against pathogens and foreign substances
  • Pathogens include bacteria, viruses, fungi, and parasites
  • Foreign substances include toxins, allergens, and transplanted tissues
• Innate immunity is the first line of defense and is non-specific
  • Includes physical barriers (skin, mucous membranes), chemical barriers (enzymes, pH), and cellular components (phagocytes, natural killer cells)
  • Innate immune responses are rapid but do not provide long-lasting protection
• Adaptive immunity is specific and provides long-lasting protection
  • Involves the production of antibodies by B-lymphocytes (humoral immunity)
  • Involves the activation of T-lymphocytes that directly attack infected or abnormal cells (cell-mediated immunity)
• Antigens are substances that trigger an immune response
  • Antigens include proteins, polysaccharides, and lipids on the surface of pathogens or foreign cells
  • Antibodies and T-cell receptors specifically recognize and bind to antigens
• Cytokines are signaling molecules that regulate immune responses
  • Produced by immune cells and other cell types
  • Include interleukins, interferons, and tumor necrosis factors
  • Cytokines stimulate the proliferation and differentiation of immune cells and coordinate the immune response

Types of Immunity

• Passive immunity is the transfer of preformed antibodies from one individual to another
  • Occurs naturally through the placenta (maternal antibodies) and breast milk (colostrum)
  • Can be artificially induced through the administration of immune globulin (antibody) preparations
  • Provides immediate but short-lived protection
• Active immunity is the production of antibodies by an individual's own immune system
  • Occurs naturally through exposure to pathogens or foreign substances
  • Can be artificially induced through vaccination with weakened or inactivated pathogens or their components
  • Provides long-lasting protection due to the development of memory B and T cells
• Herd immunity is the indirect protection of unvaccinated individuals in a population
  • Occurs when a high percentage of the population is vaccinated or has developed immunity through natural exposure
  • Reduces the spread of infectious diseases by limiting the number of susceptible individuals
• Immunological memory is the ability of the immune system to respond more rapidly and effectively to a previously encountered antigen
  • Involves the development of memory B and T cells during the primary immune response
  • Memory cells quickly proliferate and differentiate into effector cells upon re-exposure to the antigen
• Immunological tolerance is the lack of an immune response to self-antigens
  • Develops during lymphocyte maturation through the elimination or inactivation of self-reactive lymphocytes
  • Prevents autoimmune disorders, in which the immune system attacks the body's own tissues

Immune Response Process

• Antigen presentation is the process by which antigen-presenting cells (APCs) display antigens to lymphocytes
  • Dendritic cells, macrophages, and B cells are professional APCs
  • APCs process antigens and present them on their surface in conjunction with MHC molecules
• Clonal selection is the activation and proliferation of lymphocytes that specifically recognize an antigen
  • Antigen-specific lymphocytes are selected from a diverse pool of naive lymphocytes
  • Selected lymphocytes undergo clonal expansion, producing a large number of identical effector cells
• Effector functions are the mechanisms by which activated lymphocytes eliminate pathogens and infected cells
  • B cells differentiate into plasma cells that secrete antibodies
    • Antibodies neutralize toxins, opsonize pathogens for phagocytosis, and activate complement
  • Cytotoxic T cells directly kill infected or abnormal cells through the release of perforin and granzymes
  • Helper T cells secrete cytokines that stimulate the activity of other immune cells
• Immunological memory is established through the development of memory B and T cells
  • Memory cells are long-lived and can quickly respond to re-exposure to the same antigen
  • Memory cells provide the basis for long-lasting immunity and the effectiveness of vaccines
• Regulation of the immune response involves mechanisms to prevent excessive or prolonged inflammation
  • Regulatory T cells suppress the activity of other immune cells through the secretion of inhibitory cytokines
  • Apoptosis of effector cells occurs once the pathogen has been eliminated, preventing tissue damage

Disorders and Diseases

• Immunodeficiencies are disorders characterized by a weakened or absent immune response
  • Primary immunodeficiencies are genetic disorders that affect the development or function of immune cells (SCID, XLA)
  • Secondary immunodeficiencies are acquired and can be caused by malnutrition, certain medications, or infections (AIDS)
• Autoimmune disorders occur when the immune system mistakenly attacks the body's own tissues
  • Examples include rheumatoid arthritis, systemic lupus erythematosus (SLE), and multiple sclerosis
  • Autoimmune disorders can be organ-specific (Hashimoto's thyroiditis) or systemic (SLE)
• Allergies are hypersensitivity reactions to normally harmless substances (allergens)
  • Mediated by IgE antibodies and the release of histamine and other inflammatory mediators
  • Symptoms can range from mild (hay fever) to severe (anaphylaxis)
• Cancers of the lymphatic system include lymphomas and leukemias
  • Lymphomas are malignancies of lymphocytes that form solid tumors in lymph nodes and other tissues (Hodgkin's, non-Hodgkin's)
  • Leukemias are malignancies of blood-forming cells that circulate in the bloodstream and bone marrow (ALL, CLL)
• Infections of the lymphatic system can be caused by various pathogens
  • Bacteria (streptococcus, staphylococcus) can cause lymphadenitis, an inflammation of the lymph nodes
  • Viruses (EBV, CMV) can infect lymphocytes and cause infectious mononucleosis and other disorders

Clinical Applications

• Lymph node biopsy is a diagnostic procedure that involves removing a lymph node for examination
  • Used to diagnose lymphomas, metastatic cancers, and certain infections
  • Lymph nodes are typically biopsied when they are enlarged, firm, or fixed to surrounding tissues
• Immunotherapy is a type of cancer treatment that harnesses the immune system to fight cancer cells
  • Monoclonal antibodies are lab-produced antibodies that target specific antigens on cancer cells (rituximab, trastuzumab)
  • Checkpoint inhibitors are drugs that block inhibitory signals on T cells, enhancing their ability to kill cancer cells (ipilimumab, nivolumab)
  • CAR T-cell therapy involves genetically modifying a patient's T cells to target and destroy cancer cells
• Vaccination is the administration of a vaccine to stimulate an immune response and provide protection against infectious diseases
  • Vaccines contain weakened or inactivated pathogens, or their components (antigens)
  • Vaccines stimulate the production of antibodies and the development of memory B and T cells
  • Herd immunity can be achieved when a high percentage of the population is vaccinated
• Immunosuppressive therapy is used to suppress the immune system in certain conditions
  • Used to prevent rejection of transplanted organs and tissues
  • Used to treat autoimmune disorders by reducing inflammation and tissue damage
  • Immunosuppressive drugs include corticosteroids, calcineurin inhibitors (cyclosporine), and antimetabolites (methotrexate)
• Diagnostic tests for immune disorders include blood tests and imaging studies
  • Complete blood count (CBC) can reveal abnormalities in lymphocyte numbers and morphology
  • Immunoglobulin levels can be measured to assess antibody production and humoral immunity
  • Lymph node and spleen enlargement can be detected by physical examination, ultrasound, or CT scan

Connections to Other Body Systems

• The lymphatic system is closely associated with the cardiovascular system
  • Lymphatic vessels parallel blood vessels and return fluid from tissues to the bloodstream
  • The thoracic duct, the largest lymphatic vessel, drains into the left subclavian vein
• The lymphatic system interacts with the digestive system in the absorption of dietary lipids
  • Lacteals in intestinal villi absorb chylomicrons and transport them to the bloodstream via the thoracic duct
  • Peyer's patches in the small intestine are sites of immune surveillance and response to ingested antigens
• The lymphatic system is involved in the inflammatory response, which is a protective mechanism against tissue damage and infection
  • Inflammation involves the recruitment of immune cells, the release of cytokines, and the increased permeability of blood vessels
  • Chronic inflammation can contribute to the development of various diseases, including cardiovascular disease and cancer
• The lymphatic system plays a role in the metastasis of cancer cells
  • Cancer cells can enter lymphatic vessels and spread to regional lymph nodes and distant organs
  • The presence of cancer cells in lymph nodes is an important prognostic factor and guides treatment decisions
• The lymphatic system interacts with the integumentary system in the defense against pathogens
  • Skin-associated lymphoid tissue (SALT) is found in the dermis and provides a barrier against invading microorganisms
  • Langerhans cells in the epidermis are specialized antigen-presenting cells that initiate immune responses to skin antigens