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Student Guide: Modeling Blood Flow with Straws

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Summary

What do you think happens to the flow of blood in people's bodies when disease narrows their arteries? You will find out by making and testing models of different artery sizes using straws, disposable cups, and water.

Useful Vocabulary

  • Circulatory system: The set of body parts, including the heart, lungs, veins, and arteries, that help move blood all around the body.
  • Veins: The small tubes that run throughout the body returning blood to the heart. When the body has removed oxygen from the blood, it travels through the veins, which are usually blue.
  • Arteries: The small tubes that run throughout the body carrying blood away from the heart. They are usually red and hold blood that is full of oxygen for the rest of the body to use.
  • Diameter: The length across a circle or tube. A quarter has a larger diameter than a dime.
  • Coronary heart disease: A type of heart disease where poor nutrition, like foods high in fat and cholesterol, causes the walls of the artery to become thicker. As the walls become thicker, the diameter of the artery (the size of the tube the blood can move through) gets smaller. This can lead to serious health problems, including heart attacks.
  • Flow rate: The amount of liquid, like blood, that can pass through a tube over a period of time. A tube that has a gallon of milk flow through it in a minute has a faster flow rate than a tube that has a cup of milk flow through in the same minute.

Materials

To do this activity you will need:

  • Plastic or Styrofoam cups (2). Both have holes punched in them; one hole should be larger than the other one.
  • Straws (2). One will have a larger diameter than the other.
  • Play dough, clay, or silly putty
  • Pan or basin for catching water
  • Water

Directions

  1. For each cup, put one straw in the hole. Put the larger diameter straw in the cup with the larger hole. Put the smaller diameter straw in the cup with the smaller hole. Make sure the hole is not squeezing the straw and narrowing it.
  2. Use play dough, clay, or silly putty to seal the hole inside the cup and around the straw so that water cannot leak out of the hole. Why do you not want water to leak out the holes? How might that change your experiment?
  3. Make sure the straws are pointing down so that the water can flow out.
  4. Do you think the straws will have the same or different flow rates? Why?
Classroom activity Modeling blood flow Put 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.
Figure 1. Put 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.
  1. Put both cups in a pan or basin. Quickly fill both cups with water. Fill them to the same level. Either fill the cups at the same time, or fill the cup with the smaller diameter straw first. Watch carefully to see if water stops flowing from the two cups at the same or different times.
  2. If you have enough water, refill the cups and watch again. Do this several times to see if the results are always the same.
Classroom activity Modeling blood flow Water will flow out of both straws.  Watch and see if the water stops flowing out of the straws at the 
same or different times.
Figure 2. Water will flow out of both straws. Watch and see if the water stops flowing out of the straws at the same or different times.
  1. Does water stop flowing out of the two cups at the same or different times? What does this tell you about the flow rate? Is the flow rate of a straw with a large diameter the same or different from the flow rate of a straw with a small diameter?
  2. Based on your experiment what do you think happens to the flow rate of blood during coronary heart disease? Hint: Remember that people with coronary heart disease have arteries with smaller diameters.