Facilitator/Educator Guide: Modeling Blood Flow with Straws
What happens to the flow of blood when heart disease narrows a person's arteries? Create a model to illustrate the answer using straws, disposable cups, and colored water.
To be healthy, every part of the human body needs to be supplied with oxygen and nutrients. The blood's job is to travel through the body's circulatory system (heart, lungs, veins, and arteries) picking up nutrients and oxygen and delivering them to the other parts of the body. The heart acts as a powerful pump that generates the force necessary to move the blood around the circulatory system. When something goes wrong with the body's circulatory system, it can lead to serious health consequences or death.
The most common problem with the circulatory system is coronary heart disease, also called coronary artery disease. Coronary heart disease is caused by the buildup of cholesterol and other material, called plaques, in the arteries. This buildup is known as atherosclerosis. Over time as the plaques grow larger, the arteries, which usually carry oxygenated blood to the heart, become narrower. As the arteries narrow they cannot carry as much blood to the heart. The decrease in oxygenated blood can lead to chest pains and heart attacks. The plaques sometimes become dislodged and form blood clots that block the blood flow—this can also cause heart attacks and strokes.
In this science activity students can model what happens to blood flow when coronary heart disease narrows a person's arteries by comparing the flow of water (blood) through straws (arteries) of different diameters.
This science activity can be used as a starting point for a variety of science and health discussions. Here are a few examples of questions that can be used to start a discussion:
- Do you expect the cups to empty at the same or different rates? If you chose different rates, which one will empty first? Why?
- How can coronary heart disease be prevented?
- What part of the circulatory system does the water represent in this activity? How about the other materials used? Do they represent parts of the circulatory system?
- Come up with examples of other places where diameter and flow rate matter. Think about examples in your home or in manufacturing.
Needed for preparing ahead:
- Scissors (1)
- Food coloring (optional)
- Water (enough to fill all the cups at least once)
Needed for each demo or small group at the time of the science activity:
- Container for pouring water (1)
- Plastic or Styrofoam cups (2); easier with 16 oz size or larger
- Straws (2); make sure one has a larger diameter than the other
- Play dough, clay, or silly putty
- Pan or basin for catching water
|Figure 1. A few simple household materials are all that are needed to do this fun science activity.|
What to Do
Prepare Ahead (< 10 minutes)
- Use the scissors to poke or cut a hole in the side of each cup, near the bottom. The holes should be approximately the same distance from the bottom of each cup. Widen the hole enough to comfortably fit each straw. The wider straw will need a bigger hole.
- Trim the straws to approximately 2 inch lengths.
- (Optional) Add food coloring to the water. This will make it easier for students to observe what is happening.
Science Activity (< 10 minutes)
- Each group should have two cups: one with a large hole for the wider straw and one with a smaller hole for the slimmer straw. For each cup, put one straw in the hole. Make sure the hole is not squeezing the straw and narrowing it.
- Use play dough, clay, or silly putty to seal the inside of the hole around the straw so that water cannot leak out of the hole.
|Figure 2. Place play dough, or a similar material, around the straw on the inside of the cup to prevent leaking. Water should only be able to escape through the straw.|
- Place both cups in a pan or basin. Quickly fill both cups with water. Through which straw does the water flow faster? Tips: The water is easier to see if it is colored. Either fill the cups at the same time, or fill the cup with the smaller diameter straw first. Make sure the straws are pointing down so that the water can flow out.
|Figure 3. Water will flow out of both straws, but at different rates.|
You should see that the cup with the smaller diameter straw empties more slowly. This is because a pipe or straw with a smaller diameter has a slower flow rate. This is also what happens in coronary heart disease. The arteries (straws) become narrower (smaller diameter) due to the build-up of plaques. As the arteries narrow, they carry blood (water) less quickly to the heart.
For Further Exploration
This science activity can be expanded or modified in a number of ways. Here are a few options:
- Use play dough or other substances to model plaques inside the arteries (straws). What happens when the plaque breaks away from the artery wall?
- Make the activity quantitative by having students use stopwatches to time how long it takes to empty the cup with different diameter straws. Graph the data.