Immune System

The immune system is a complex network of cells, tissues, and organs that helps the body fight infections and other diseases. It includes barrier defenses like the skin and mucous membranes as well as immune cells (white blood cells) and organs such as lymph nodes, spleen, and thymus, which work together to identify and destroy pathogens.

• The immune system is divided into <u>innate immunity</u> (rapid, non-specific defense) and <u>adaptive immunity</u> (slower, specific defense with memory). Innate immunity includes general defenses like skin, inflammation, and phagocytic cells, while adaptive immunity involves lymphocytes (B-cells and T-cells) and antibody production.
• Swollen lymph nodes during an infection are a sign of the immune system in action - lymph nodes swell as they fill with multiplying immune cells fighting the pathogen.
• Vaccines work by training the adaptive immune system to recognize a pathogen, so if the real pathogen appears, the immune system's memory cells respond faster and prevent illness.

• If a question asks which system defends the body against bacteria, viruses, and other pathogens -> it's referring to the immune system (with components like white blood cells, antibodies, etc.).
• If you see a scenario of "swollen glands" (swollen lymph nodes) or an increase in antibody levels after an exposure -> that indicates the immune system responding to an infection.
• If a question contrasts a fast, non-specific response vs. a slower, specific memory-forming response to an infection -> it's highlighting innate immunity vs. adaptive immunity as parts of the immune system.