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Medical Science
How the Immune System Fights Germs
the Immune System Fights Germs
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The immune system is the body’s defense network against germs such as bacteria, viruses, fungi, and parasites. It matters because many germs can multiply quickly, damage tissues, and spread through the body if they are not controlled. Immune cells, proteins, and organs work together to detect invaders and remove them while protecting healthy cells. This defense system is active in the blood, skin, lungs, gut, lymph nodes, and nearly every tissue.
Key Facts
- White blood cells identify, attack, and remove germs from the body.
- Inflammation increases blood flow and brings immune cells to an infected area.
- Phagocytes engulf germs by phagocytosis and break them down inside the cell.
- Antibodies bind to specific antigens on germs and help mark them for destruction.
- Vaccines train immune memory without requiring a person to suffer the full disease.
- Basic reproduction estimate for infection spread: new infected cells = infected cells x replication factor.
Vocabulary
- Pathogen
- A pathogen is a disease-causing germ, such as a bacterium, virus, fungus, or parasite.
- White blood cell
- A white blood cell is an immune cell that helps detect, attack, or coordinate defenses against infection.
- Antibody
- An antibody is a Y-shaped protein that binds to a specific antigen on a germ or infected cell.
- Phagocytosis
- Phagocytosis is the process in which an immune cell surrounds, engulfs, and digests a particle such as a bacterium.
- Immune memory
- Immune memory is the ability of the immune system to respond faster and stronger to a germ it has encountered before.
Common Mistakes to Avoid
- Thinking all germs are the same is wrong because bacteria and viruses have different structures and are fought in different ways.
- Assuming antibiotics kill viruses is wrong because antibiotics target bacterial features, not viral replication inside host cells.
- Believing inflammation is always harmful is wrong because controlled inflammation helps bring immune cells and chemicals to the site of infection.
- Confusing vaccines with treatments is wrong because vaccines mainly prepare immune memory before exposure, while treatments act after illness begins.
Practice Questions
- 1 A sample contains 200 bacteria, and the number doubles every 30 minutes. How many bacteria are present after 2 hours if nothing stops their growth?
- 2 A phagocyte can engulf 12 bacteria per hour. If 8 phagocytes are active at the same rate, how many bacteria can they engulf in 3 hours?
- 3 Explain why a second infection by the same virus is often fought faster than the first infection, using the idea of immune memory.