Ch 21

Lymphatic System Functions

Front: What are the three primary functions of the lymphatic system?
Back: 1. Fluid Recovery - Reabsorbs 15% of fluid lost from capillaries (2-4 L/day).
2. Immunity - Picks up foreign cells and chemicals, passes through lymph nodes to activate immune responses.
3. Lipid Absorption - Lacteals in the small intestine absorb dietary lipids not absorbed by blood capillaries.

Lymphatic Vessels

Front: What are lymphatic vessels and their function?
Back: Lymphatic vessels transport lymph, a recovered fluid, through a network that includes lymph nodes, trunks, and ducts, ultimately returning it to the bloodstream.

Front: What are the six major lymphatic trunks?
Back: Jugular, subclavian, bronchomediastinal, intercostal, intestinal (unpaired), and lumbar trunks.

Flow of Lymph

Front: How does lymph move through the body without a pump like the heart?
Back: Lymph moves through rhythmic vessel contractions, skeletal muscle pumps, arterial pulsations, the thoracic pump, and one-way valves that prevent backflow.

Lymphatic Cells

Front: What are the primary types of lymphatic cells and their functions?
Back:

1. Natural Killer (NK) Cells - Attack bacteria, transplanted cells, virus-infected cells, and cancerous cells.

2. T Lymphocytes (T Cells) - Mature in the thymus, responsible for cell-mediated immunity.

3. B Lymphocytes (B Cells) - Differentiate into plasma cells that produce antibodies.

4. Macrophages - Phagocytic cells that process and present antigens to T cells.

5. Dendritic Cells - Antigen-presenting cells (APCs) that alert the immune system.

6. Reticular Cells - Contribute to the structural framework of lymphatic organs.

Lymphatic Organs

Front: What are the primary and secondary lymphatic organs?
Back:

• Primary Lymphatic Organs: Red bone marrow and thymus (where T and B cells become immunocompetent).

• Secondary Lymphatic Organs: Lymph nodes, tonsils, spleen (where immunocompetent cells are activated).

Front: What is the function of the thymus?
Back: The thymus houses developing T cells, secretes hormones (thymosin, thymopoietin), and forms the blood-thymus barrier to protect immature T cells from premature activation.

Lymph Nodes

Front: What are the two primary functions of lymph nodes?
Back: 1. Filter lymph and remove harmful substances.
2. Site for T and B cell activation.

Front: How do lymph nodes contribute to cancer metastasis?
Back: Cancer cells can enter lymphatic vessels, lodge in lymph nodes, multiply, and spread to other tissues.

Innate vs. Adaptive Immunity

Front: What are the differences between innate and adaptive immunity?
Back:

• Innate Immunity: General defenses, present at birth, non-specific, includes skin, mucous membranes, leukocytes, and inflammatory responses.

• Adaptive Immunity: Specific responses, involves memory, includes T and B cells that recognize and attack specific pathogens.

First Line of Defense: External Barriers

Front: How does the skin protect against infection?
Back: The skin is tough (keratin), dry, nutrient-poor, and secretes antimicrobial substances like dermicidin, defensins, and cathelicidins.

Front: How do mucous membranes contribute to immunity?
Back: They line body passages, secrete mucus to trap microbes, and contain lysozyme, an enzyme that destroys bacterial cell walls.

Second Line of Defense: Cells & Chemicals

Front: What are the five types of leukocytes involved in immunity?
Back: Neutrophils, eosinophils, basophils, monocytes, and lymphocytes.

Front: What is the function of natural killer (NK) cells?
Back: NK cells patrol the body and destroy infected, cancerous, or foreign cells using perforins and granzymes to induce apoptosis.

Front: What are interferons?
Back: Proteins secreted by virus-infected cells to warn neighboring cells, activate NK cells, and enhance macrophage activity.

Complement System

Front: What is the complement system, and how does it destroy pathogens?
Back: A group of 30+ plasma proteins that enhance immunity by triggering inflammation, immune clearance, phagocytosis, and cytolysis (membrane attack complex formation).

Fever & Inflammation

Front: How does fever help fight infection?
Back: Fever increases metabolic rate, accelerates tissue repair, promotes interferon activity, and inhibits microbial reproduction.

Front: What are the four cardinal signs of inflammation?
Back: Redness, swelling, heat, and pain.

Adaptive Immunity: T Cells

Front: What are the three stages of T cell development?
Back: 1. Born in bone marrow.
2. Mature in the thymus (selection process).
3. Deployed to lymphatic tissues.

Front: What are the four classes of T cells?
Back: Cytotoxic T cells (attack infected cells), Helper T cells (coordinate immunity), Regulatory T cells (prevent overreaction), Memory T cells (provide long-term immunity).

Adaptive Immunity: B Cells

Front: How do B cells function in humoral immunity?
Back: B cells recognize antigens, proliferate into plasma cells, and produce antibodies that neutralize or tag pathogens for destruction.

Front: What are the five classes of antibodies (immunoglobulins)?
Back:

• IgG: Most abundant, crosses placenta, secondary response.

• IgA: Found in secretions (tears, saliva, breast milk).

• IgM: First produced in infection, pentamer structure.

• IgE: Involved in allergic reactions and parasite defense.

• IgD: Functions in B cell activation.

Memory & Vaccination

Front: What is the difference between active and passive immunity?
Back:

• Active Immunity: Body produces its own antibodies (natural: infection; artificial: vaccine).

• Passive Immunity: Antibodies are transferred (natural: mother to baby; artificial: antibody injection).

Senescence of the Immune System

Front: How does aging affect immunity?
Back: Lymphatic tissue and red bone marrow decline, fewer immune cells are produced, and responses to infections and cancer become weaker.