The Immune System

1. The Immune System • We are surrounded by billions of bacteria and viruses. • To many of them, a human being is like a walking smorgasbord, offering nearly limitless resources that they can use for energy and reproduction. • Luckily for us, getting into the human body is not an easy task!

2. Skin • From the point of view of bacteria and viruses, the skin is thick and very hard to penetrate. • Skin also produces a variety of substances that are harmful to invaders. • Openings (eyes, nose, mouth) are protected by fluids that capture harmful attackers. • The respiratory tract also has cilia, or little tiny hairs, that move particles to the stomach. Once in the stomach, the acid kills the intruder.

3. In spite of our fantastic defenses… • Hostile invaders still manage to get into our bodies. • How? • Food • Through the nose • Scrapes in our skin What is the “magic” that keeps us healthy most of the time?

4. The Immune System! • What happens when you get a cut? • When invaders enter the body, cells are destroyed. • The dying cells trigger an automatic response called inflammation. • (Inflammation is the body’s equivalent to a burglar alarm.) • Once it goes off, it draws defensive cells to the damaged area in great numbers. • It is because of all of these damaged cells, extra cells, and increased blood flow, that redness and swelling occurs.

5. Immune Cells: The Defense • The cells of the immune system are a highly effective defense force. • Immune system cells work together with different proteins to seek out and destroy anything foreign or dangerous that enters your body. • It takes some time for the immune cells to be activated, but once they’re operating at full strength, there are a very few hostile organisms that stand a chance.

6. Types of immune cells ~ a wide variety… • White blood cells are produced in the bone marrow. • Some seek out and devour invading organisms… • Others destroy infected or mutated body cells… • Another type has the ability to release special proteins called antibodies that mark intruders for destruction by other cells.

7. THE COOLEST THING ABOUT IMMUNE CELLS • Immune cells have the ability to “remember” enemies that it has fought in the past. • If the immune system recognizes an invader it will strike more quickly and more fiercely against it. • When this happens, we say that the body has become immune.

8. Bacteria and Viruses: Our Main Enemies • Most bacteria are free living, while others live in or on other organisms. • Many bacteria produce toxins (poisons) that damage the body. • NOT ALL BACTERIA ARE HARMFUL! • Some are neutral and many are even desirable as they fulfill important functions in the body.

9. Viruses – something a little different… • Bacteria can reproduce all on their own. • VIRUSES CANNOT! • Viruses hijack body cells of humans or other species and trick them into producing new viruses that can then invade other cells. • FREQUENTLY THE HOST CELL IS DESTROYED IN THE PROCESS!

10. Pathogens and Antigens • In daily life we might speak of viruses, bacteria and toxins. • However, when talking about the immune system, you’ll often come across the words antigen and pathogen. • An antigen is a foreign substance that triggers a response from the immune system. • Antigens are often found on surfaces of bacteria and viruses. • A pathogen is a microscopic organism that causes sickness. • Hostile bacteria and viruses are examples of pathogens.