Ch. 20: The Lymphatic System

Overview of the Lymphatic System

The lymphatic system is a network of tissues and organs that help rid the body of toxins, waste, and other unwanted materials. Its primary function is to transport lymph, a fluid containing infection-fighting white blood cells, throughout the body.

• Peyer's patches: Aggregated lymphoid nodules found in the wall of the small intestine, especially the ileum. They monitor intestinal bacteria populations and prevent the growth of pathogenic bacteria.

• Anatomy of a lymph node: Lymph nodes are small, bean-shaped structures that filter lymph and house lymphocytes. They consist of a cortex (outer region) and medulla (inner region).

• General lymphatic circulation: Lymph is collected from tissues, passes through lymphatic vessels and nodes, and eventually drains into the venous system via the thoracic duct or right lymphatic duct.

• MALT (Mucosa-Associated Lymphoid Tissue): Lymphatic tissues found in mucosal linings, such as the gastrointestinal, respiratory, and genitourinary tracts. Examples include tonsils, Peyer's patches, and the appendix.

• Function and location of the lacteal: Lacteals are specialized lymphatic capillaries in the villi of the small intestine that absorb dietary fats and transport them as chyle.

• Functions of the spleen: The spleen filters blood, removes old or damaged red blood cells, and helps mount immune responses against blood-borne pathogens.

• Anatomy and function of the thymus: The thymus is located in the mediastinum and is the site of T cell maturation. It is most active during childhood.

• Types and locations of tonsils: Tonsils are lymphoid tissues located in the pharynx. Types include palatine tonsils (sides of the throat), pharyngeal tonsil (adenoids, in the nasopharynx), and lingual tonsil (base of the tongue).

• Pathway of lymph from capillaries to cardiovascular system: Lymphatic capillaries → lymphatic vessels → lymph nodes → lymphatic trunks → lymphatic ducts → subclavian veins.

• Functions of the lymphatic system:

  • Returns excess tissue fluid to the bloodstream

  • Absorbs fats and fat-soluble vitamins from the digestive system

  • Defends against pathogens and disease

Key Terms and Examples

• Lymph: Clear fluid that circulates through the lymphatic system.

• Lymphocyte: Type of white blood cell involved in immune responses.

• Example: Swollen lymph nodes during infection indicate active immune response.

Ch. 21: The Immune System

Overview of Immune Responses

The immune system protects the body from infectious agents and other foreign substances. It consists of innate (nonspecific) and adaptive (specific) defenses.

• B cell response to antigen: B cells recognize antigens and differentiate into plasma cells, which produce antibodies.

• Plasma cells: Differentiated B cells that secrete large amounts of antibodies.

• Types of antibodies: Five main classes: IgG, IgA, IgM, IgD, IgE. Each has distinct roles in immune defense.

• Complement activation: A series of protein interactions that enhance immune responses, leading to pathogen lysis. (Classical pathway)

• Opsonization: Process by which pathogens are marked for phagocytosis by coating them with antibodies or complement proteins.

• Natural killer (NK) cells: Lymphocytes that destroy virus-infected cells and tumor cells by inducing apoptosis.

• Parts of the innate immune system: Includes physical barriers (skin, mucous membranes), phagocytes, NK cells, inflammation, and complement system.

• Advantages of adaptive immunity: Specificity, memory, and ability to mount stronger responses upon re-exposure to the same antigen.

• Antigen: Any substance that can induce an immune response, typically a protein or polysaccharide on the surface of pathogens.

• Primary vs. secondary immune response:

  • Primary: First exposure, slower and less robust

  • Secondary: Subsequent exposures, faster and stronger due to memory cells

• First line of defense: Physical and chemical barriers such as skin, mucous membranes, and secretions.

• Active vs. passive immunity:

  • Active: Body produces its own antibodies (e.g., after infection or vaccination)

  • Passive: Antibodies are transferred from another source (e.g., maternal antibodies, antibody therapy)

• T and B cell maturation: B cells mature in bone marrow; T cells mature in the thymus.

• Membrane attack complex (MAC): Structure formed by complement proteins that creates pores in pathogen membranes, leading to cell lysis.

• Inflammatory response events: Vasodilation, increased permeability, migration of phagocytes, and tissue repair.

• CD4 and CD8 cells:

  • CD4: Helper T cells, coordinate immune responses

  • CD8: Cytotoxic T cells, kill infected or abnormal cells

• Regulatory T cells: Suppress immune responses to prevent autoimmunity.

• MHC molecules:

  • Class I: Present on all nucleated cells, present endogenous antigens to CD8 T cells

  • Class II: Present on antigen-presenting cells, present exogenous antigens to CD4 T cells

• Hapten: Small molecule that can elicit an immune response only when attached to a larger carrier.

• Phagocyte mobilization: Movement of phagocytic cells to sites of infection or injury.

• Cytotoxic T cells: Destroy infected or cancerous cells by inducing apoptosis.

• T helper cells: Activate other immune cells by releasing cytokines.

• Classical pathway of complement activation: Initiated by antigen-antibody complexes, leading to a cascade of complement protein activation.

Key Terms and Examples

• Antibody: Protein produced by plasma cells that binds to specific antigens.

• Example: Vaccination induces active immunity by stimulating antibody production.

Comparison Table: Types of Immunity

Additional info:

• Some explanations and examples have been expanded for academic completeness.

• Equations for complement activation and immune cell differentiation have been provided in LaTeX format.