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 interstitial fluid and returned to the bloodstream, maintaining fluid balance.

• Functions: Includes immune defense, absorption of dietary fats, and removal of excess fluids from tissues.

• 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 mucosal linings, such as the gastrointestinal, respiratory, and genitourinary tracts.

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

• Thymus: Site of T cell maturation; most active during childhood and shrinks with age.

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

Functions of the Lymphatic System

• Immune Response: Houses and transports lymphocytes and other immune cells.

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

• Absorption of Fats: Lacteals in the small intestine absorb dietary lipids.

Example: Pathway of Lymph

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

Ch. 21: The Immune System

Innate and Adaptive Immunity

The immune system protects the body from pathogens through innate (nonspecific) and adaptive (specific) mechanisms.

• Innate Immunity: First line of defense; includes physical barriers (skin, mucous membranes), phagocytic cells, natural killer cells, and complement proteins.

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

• Active vs. Passive Immunity: Active immunity results from direct exposure to an antigen; passive immunity is acquired through transfer of antibodies (e.g., maternal antibodies).

Cells and Molecules of the Immune System

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

• Plasma Cells: Effector B cells that secrete antibodies.

• T Cells: Include cytotoxic T cells (destroy infected cells), helper T cells (activate other immune cells), and regulatory T cells (modulate immune response).

• Natural Killer Cells: Destroy virus-infected and tumor cells without prior sensitization.

Antibodies and Antigens

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

• Antibody: Protein produced by B cells that binds specifically to an antigen.

• Types of Antibodies: IgG, IgA, IgM, IgE, IgD; each has distinct roles in immunity.

Complement System and Opsonization

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

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

• Membrane Attack Complex (MAC): Formed by complement proteins to lyse pathogen cell membranes.

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.

Immune Responses and Mobilization

• Inflammatory Response: Sequence of events including vasodilation, increased permeability, and migration of immune cells to the site of infection.

• Phagocyte Mobilization: Movement of phagocytic cells (neutrophils, macrophages) to sites of infection.

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

Example: Classical Pathway of Complement Activation

• Antigen-antibody complex formation → activation of C1 protein → sequential activation of other complement proteins → formation of MAC and cell lysis

Key Equations and Concepts

• Antibody-Antigen Binding:

• Complement Activation (Classical Pathway):

Comparison Table: Innate vs. Adaptive Immunity

Additional info:

• Regulatory T cells help prevent autoimmune reactions by suppressing immune responses.

• Cytotoxic T cells recognize and kill infected cells presenting antigens via MHC I.

• Helper T cells activate B cells, cytotoxic T cells, and macrophages.