This demonstration models how artery size affects blood flow. Water dyed red to represent blood flows through tubes of different diameters, showing that narrower arteries restrict flow and increase resistance, similar to what happens in the human body when vessels are constricted.

1. Put on safety goggles and a lab coat.
2. Have an assistant plug the ends of both tubes (one wide, one narrow).
3. Fill a quart container with 1000 mL of water mixed with red dye.
4. Connect the container to both the ½-inch and ¼-inch tubing using nylon barb adapters.
5. Place the free ends of the tubes into two separate 1000 mL beakers.
6. Ask students to predict how much liquid will flow from each tube.
7. Have the assistant release both tubes at the same time and observe the water flow.
8. Note that the larger tube allows significantly more water to flow, while the smaller tube fills its beaker much more slowly.

📄 Heart Trouble (on page 4 of pdf) - Kirsten Johnson: https://www.unco.edu/nhs/science/pdf/demos/2007_NSTA_demos.pdf

• Use multiple tubes of different diameters to compare a wider range of flow rates.
• Try changing the height of the container to model blood pressure changes.
• Add clamps to mimic partial blockage or stress-related narrowing of arteries.

• Wear goggles to protect eyes from splashes.
• Wear a lab coat or apron to protect clothing from red dye stains.
• Clean up spills immediately to avoid staining and slipping hazards.

• What would happen to the heart of a person who has constricted vessels? (The heart would have to work harder to pump blood, increasing risk of heart disease or failure.)
• What other systems in the body would this affect? (The brain, muscles, and organs may receive less oxygen and nutrients, leading to fatigue, dizziness, or organ damage.)
• How does this model help explain why high blood pressure is dangerous? (It shows how increased resistance in arteries forces the heart to pump harder, straining the cardiovascular system.)
• What lifestyle choices or medical conditions might cause arteries to narrow? (Plaque buildup from poor diet, smoking, stress, or conditions like atherosclerosis.)