Module 10 Defense and Immunity

Flow of lymph through the lymphatic system

Lymph flows from capillaries → lymphatic vessels → lymph nodes → larger vessels → thoracic duct/right lymphatic duct → subclavian veins.

Main lymphatic organs and their functions

Lymph nodes: Filter lymph, house immune cells. Tonsils: Trap pathogens from air/food. Spleen: Filters blood, recycles red blood cells. MALT (Mucosa-Associated Lymphatic Tissue): Protects mucosal surfaces (e.g., Peyer's patches in intestine).

Nonspecific (innate) immunity

Defences present at birth that protect against any pathogen, without memory (e.g., skin, inflammation, phagocytes).

Specific (adaptive) immunity

A slower response tailored to a specific pathogen; involves B and T cells, and includes immunological memory.

Difference between innate and adaptive immunity

Innate: Immediate, general response, no memory. Adaptive: Slower, specific, develops memory for faster future responses.

Three lines of defence in the body

First line: Physical and chemical barriers (skin, mucous membranes, secretions, reflexes). Second line: Internal defenses (inflammation, fever, phagocytes, natural killer cells, antimicrobial proteins). Third line: Specific immune responses (B and T cells, antibodies).

Four cardinal signs of inflammation and their physiological causes

Redness: Increased blood flow (vasodilation). Heat: Blood carries heat to area. Swelling: Fluid and immune cells enter tissue. Pain: Due to chemicals and pressure from swelling.

Role of antigens in immunity

Antigens are foreign substances that trigger an immune response; they bind to antibodies or T-cell receptors.

B cells and their function

B cells produce antibodies. Once activated, they become plasma cells (secrete antibodies) or memory B cells.

T cells and their function

Helper T cells: Activate B cells and cytotoxic T cells. Cytotoxic T cells: Destroy infected or abnormal cells. Memory T cells: Provide faster response on re-exposure.

Active immunity

Immunity developed by the body making its own antibodies after exposure to antigen (via infection or vaccine).

Passive immunity

Immunity gained by receiving pre-made antibodies (e.g., from placenta, breast milk, or antibody injection).

Examples of naturally acquired immunity

Active: Recovering from an illness. Passive: Antibodies passed from mother to baby (placenta, breast milk).

Examples of artificially acquired immunity

Active: Vaccination. Passive: Injection of antibodies (e.g., anti-venom).