Unit 18: The Immune System
How your body tells its own cells apart from invaders, and fights off the invaders without fighting itself.
6 topics · 18 questions
Each topic is a path, not a menu: work down it in order and every question builds on the one above. Click any of them to watch the answer draw itself.
The Body's First Line of Defense
- How it worksHow do skin, mucus, and stomach acid physically and chemically block pathogens before they enter the body?
- Common mistakeWhy isn't skin just a passive physical barrier with no chemical defenses of its own?
- Going furtherWhat happens to a pathogen's chances of infecting the body once it gets past a cut in the skin?
Your turn1 of 2
Unbroken skin covering the body blocks the vast majority of pathogens a person encounters every day, long before the immune system's white blood cells ever get involved. Why does unbroken skin stop far more infections than most people realize?Innate Immunity: Inflammation and White Blood Cells
- How it worksHow do white blood cells called phagocytes engulf and destroy invading pathogens?
- How it worksHow does the inflammatory response increase blood flow and immune cells to an injured area?
- Common mistakeWhy doesn't innate immunity target one specific pathogen the way adaptive immunity does?
Your turn1 of 2
An infected cut on your finger becomes visibly red, feels warm to the touch, and swells up within minutes, long before you can see any actual pus or healing taking place. Why does an infected cut turn red, warm, and swollen so quickly?Adaptive Immunity: B Cells and Antibodies
- How it worksHow do B cells recognize a specific antigen and multiply into cells that produce matching antibodies?
- How it worksHow do antibodies mark a pathogen for destruction without directly killing it themselves?
- Common mistakeWhy doesn't a single antibody work against every type of pathogen?
Your turn1 of 2
The first time your body encounters a brand-new virus, it can take several days to mount a full immune response, even though your immune system fights off many familiar pathogens far more quickly. Why does your body take days to fully fight off a brand-new virus it's never seen before?T Cells and Cell-Mediated Immunity
- How it worksHow do cytotoxic T cells identify and destroy body cells that display infected markers?
- Common mistakeWhy isn't a T cell the same kind of immune cell as a B cell even though both fight infection?
- Ties togetherHow do helper T cells coordinate both the B cell and cytotoxic T cell response during an infection?
Your turn1 of 2
A virus-infected body cell displays fragments of viral protein on its own surface, marking itself in a way that a cytotoxic T cell can detect and respond to by destroying that infected cell. Why can your immune system destroy your own cells once they've been infected by a virus?How Vaccines Train the Immune System
- How it worksHow does exposing the immune system to a weakened or inactive pathogen create long-lasting memory cells?
- Common mistakeWhy doesn't a flu vaccine give you a mild case of the actual flu?
- Ties togetherHow do memory B cells created by a vaccine let your body respond faster the next time it meets the real pathogen?
Your turn1 of 2
A vaccine exposes your immune system to a weakened or inactive version of a pathogen, training your body to recognize it, without causing the severe illness the actual live pathogen would cause. Why does getting a vaccine protect you from a disease without ever making you seriously sick?Allergies and Autoimmune Disease
- How it worksHow does an allergic reaction happen when the immune system overreacts to a normally harmless substance?
- Going furtherWhat happens in an autoimmune disease when the immune system starts attacking the body's own healthy cells?
- Common mistakeWhy isn't an allergic reaction the immune system correctly identifying a genuine threat?
Your turn1 of 2
A peanut protein poses no danger to most people who eat it, yet in someone with a peanut allergy, that same harmless protein can trigger a severe, even life-threatening immune reaction. Why does a harmless peanut protein trigger a dangerous immune reaction in someone with a peanut allergy?