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.

• Lymphatic Circulation: Lymph is collected from tissues and returned to the bloodstream, maintaining fluid balance and contributing to immune defense.

• Functions: Includes fluid recovery, immunity, and lipid absorption.

• Pathway of Lymph: Lymph flows from lymphatic capillaries to lymphatic vessels, through lymph nodes, and eventually drains into the cardiovascular system via the thoracic duct or right lymphatic duct.

Lymphatic Tissues and Organs

• Lymph Nodes: Small, bean-shaped structures that filter lymph and house lymphocytes. Anatomy includes cortex (with follicles) and medulla.

• Peyer's Patches: Aggregated lymphoid nodules found in the small intestine, important for monitoring intestinal bacteria populations and preventing the growth of pathogenic bacteria.

• MALT (Mucosa-Associated Lymphoid Tissue): Lymphatic tissues found in mucous membranes throughout the body, including tonsils, Peyer's patches, and the appendix.

• Tonsils: Lymphatic tissue located in the pharynx; types include palatine, pharyngeal (adenoids), and lingual tonsils.

• Spleen: Largest lymphatic organ; filters blood, removes old red blood cells, and helps mount immune responses.

• Thymus: Located in the mediastinum; site of T cell maturation, most active during childhood.

Functions of the Lymphatic System

• Immune Response: Houses and transports immune cells, filters pathogens from lymph.

• Fluid Balance: Returns excess interstitial fluid to the bloodstream.

• Lipid Absorption: Absorbs dietary lipids from the small intestine via lacteals.

Example: Pathway of Lymph

• Lymphatic capillaries → lymphatic vessels → lymph nodes → lymphatic trunks → lymphatic ducts → subclavian veins

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) immunity.

• Innate Immunity: First line of defense; includes physical barriers, phagocytes, and inflammation.

• Adaptive Immunity: Specific response involving lymphocytes (B cells and T cells) and the production of antibodies.

Cells and Molecules of the Immune System

• B Cells: Respond to antigens by differentiating into plasma cells, which produce antibodies.

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

• Antibodies: Proteins that bind to specific antigens; five types include IgG, IgA, IgM, IgD, and IgE.

• Natural Killer (NK) Cells: Lymphocytes that destroy virus-infected cells and tumor cells.

• T Cells: Include helper T cells (CD4+), cytotoxic T cells (CD8+), and regulatory T cells; involved in cell-mediated immunity.

Immune System Functions and Processes

• Opsonization: Process by which antibodies coat pathogens, enhancing phagocytosis.

• Complement Activation: Series of proteins that enhance immune responses; classical pathway is triggered by antigen-antibody complexes.

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

• Phagocyte Mobilization: Movement of phagocytic cells to sites of infection during inflammation.

Immunity Types and Responses

• Active Immunity: Results from direct exposure to an antigen; can be natural (infection) or artificial (vaccination).

• Passive Immunity: Results from transfer of antibodies; can be natural (maternal antibodies) or artificial (antibody therapy).

• Primary vs. Secondary Immune Response: Primary response is slower and less robust; secondary response is faster and stronger due to memory cells.

Major Histocompatibility Complex (MHC)

• MHC Class I: Present on all nucleated cells; present endogenous antigens to cytotoxic T cells.

• MHC Class II: Present on antigen-presenting cells; present exogenous antigens to helper T cells.

Vaccines and Immunization

• Vaccines: Stimulate adaptive immunity by exposing the body to antigens without causing disease.

Key Terms and Definitions

• Antigen: Any substance that can induce an immune response.

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

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

• Cytotoxic T Cells: Destroy infected or abnormal cells.

• T Helper Cells: Activate other immune cells by releasing cytokines.

Example: Classical Pathway of Complement Activation

• Antigen-antibody complex formation → activation of C1 protein → cascade of complement proteins → formation of MAC → lysis of pathogen

Table: Comparison of Innate and Adaptive Immunity

Key Equations

• Antibody-Antigen Binding:

• Complement Activation (Classical Pathway):