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Activity 1-1: The Blood-Brain Barrier (BBB)

PLAN

Summary Students explore the relationship between the solubility properties of molecules and their ability to cross the blood-brain barrier. They investigate separation and mixing of like and unlike liquids to learn how “like” liquids will mix and “unlike” liquids will remain separate from each other.

Objectives

Students:

\checkmark distinguish between water-soluble and oil-soluble liquids.

\checkmark describe the relationship between a substance's solubility and protecting the brain.

\checkmark explain the role of the blood-brain barrier in protecting the brain.

\checkmark demonstrate and explain the effects on the BBB of an injury to the head.

Student Materials

Per student

  • Activity Report

Per group

  • Safety goggles
  • 6 test tubes with stoppers
  • Test-tube rack
  • Marking pen
  • Masking tape
  • Clear cooking oil (to represent the membranes of the BBB)
  • Sesame or motor oil (to represent a fat-soluble substance)
  • Water with a little red food coloring (to represent blood)
  • Blue food coloring (to represent a water-soluble substance)
  • Alcohol
  • 3 eyedroppers
  • Paper towels
  • Colored pencils (red and blue)

Teacher Materials

  • Diagram of brain in skull
  • Diagram/model of the Blood-Brain Barrier
  • Activity Report Answer Key

Advance Preparation

Collect materials for demonstration or for each student team.

Diagrams of the brain in the skull can be at each lab table or displayed in the front of the room.

Have student texts available.

Set up waste containers for the disposal of liquids.

Estimated Time Approximately one 50-minute class period

Interdisciplinary Connections

Language Arts Students can use expository writing or poetry to explain how the BBB protects the brain.

Prerequisites and Background Information

Students should have completed the Mini Activity: Egghead.

Students should have some knowledge of what happens to chemicals in the body: where they go, how they work, and how they are excreted. They need to have some knowledge of how drug receptors work. They should have some knowledge of how the actual effects of drugs are related to the route or entry into the body, prior exposure to the drug, age, health, as well as dose. They also need to know that toxicity differs from the usual drug effect.

The blood-brain barrier, which is a hurdle interposed between brain capillaries and nerve and glial cells, keeps most harmful substances out of the brain while keeping brain chemicals in. For a drug to traverse the barrier and activate brain receptors, the drug needs to be small (low molecular weight) and nonpolar, i.e., lipid soluble. This activity demonstrates partition coefficients and reveals that water-soluble substances stay in the water phase and go where water goes, and that lipid-soluble substances remain in the oil and go across the lipid blood-brain barrier better and stick in the fatty tissue of the brain better.

Other processes can be demonstrated. For example, use liquid dish-washing detergent to demonstrate detergent action on the oil-water interface-i.e., bile salt action and micelle formation. Interpose a semipermeable membrane and discuss the relation between transport of a substance and its concentration (osmotic) gradient.

As students explore solubility properties of different molecules and relate them to the BBB, some may ask if there are molecules that are soluble in both oil and water. The answer to this question is “yes.” An example of this type of molecule is a detergent or alcohol. Soap can function as an acid or base and has emulsifying properties. In answering why these materials do not break down the BBB, point to the difference between this activity and the actual BBB, which consists of membranes.

IMPLEMENT

Introduce Activity 1-1 by reviewing the definition of solubility properties.

Include this activity at least as a demonstration, but preferably as a student activity.

CAUTIONS:

Plastic containers are safer. However, if you use glass, remind students of the care necessary in working with glass containers. Wear goggles. Display the safety rules. Make sure students wear safety goggles during all lab activities. Review procedures for eye safety and washing if accidental splashes occur. Caution students not to rub their eyes during the lab and to wash hands thoroughly after the lab.

Steps 1-3 Set up waste containers for disposing liquids. Make sure the test tubes are labeled correctly. Act as a model for students by wearing goggles.

Steps 4-5 Discuss student predictions. Compare predictions with actual results.

Step 6 Test tubes E and F are set up to demonstrate that some molecules are soluble in both water and oil.

Step 7 Discuss the findings recorded on the Activity Reports and the answers to the Activity Report questions.

Extend Activity 1-1 by having students conduct research. They can learn more about the blood-brain barrier and how it is affected by drug use or brain injury. This activity is an excellent “bridge” activity to connect with the Circulation unit and Lives of Cells unit.

Helpful Hints

Water colored red with food coloring: use enough food coloring to create a red color to represent the blood.

Cooking oil: a generic brand is sufficient.

Review with students what each of these materials represents before they begin.

ASSESS

Use the model of the brain and the written responses to the Activity Report to assess if students can

\checkmark explain the meaning of the word soluble.

\checkmark describe how to classify liquids as water soluble or oil soluble.

\checkmark identify which types of liquids “mix” and which liquids remain separated.

\checkmark demonstrate how the blood-brain barrier transports nutrients to the brain cells and prevents harmful substances from reaching the brain cells.

\checkmark explain how an injury to the head can disrupt the effectiveness of the BBB.

Self-Portraits Your nervous system is as unique as your fingerprints. Your brain makes you who you are. Think about the following questions and write a few responses to share with your class. Who are you? What makes you unique? Do the things that make you unique involve your brain?

What aspects of yourself and your brain interest you the most? Do you ever surprise yourself? Have you ever heard yourself say something and wonder where the thoughts came from? Explain your responses.

Activity 1-1: The Blood-Brain Barrier (BBB) – Activity Report Answer Key

  • Sample answers to these questions will be provided upon request. Please send an email to teachers-requests@ck12.org to request sample answers.
  1. Observe Test Tube A. Make a labeled drawing in color of the test tube and its contents.
    1. Do the water and oil mix?
    2. What happens when you shake the test tube?
  2. Observe Test Tube B. Make a labeled drawing of the test tube and its contents before and after adding the drops of blue food color. If the blue color is a water-soluble chemical, where would it go if it reached the brain in the bloodstream?
  3. Observe Test Tube C. Make a labeled drawing of the test tube and its contents before and after adding the motor or sesame oil. If the colored oil is a fat-soluble chemical, where would it go if it reached the brain in the bloodstream?
    1. Predictions of shaking Test Tube D for 10 seconds. Answers will vary.
    2. Results of shaking Test Tube D for 10 seconds.
    3. Explain any differences between your predictions and your observed results.
    4. If there are water-soluble and fat-soluble chemicals circulating in your blood, which is more likely to cross your BBB? Why?
    1. Describe your results from the experiment with Test Tubes E and F.
    2. How do these results differ from your observations on Test Tubes Band C?
    3. Do you think it is easy for alcohol to cross the BBB?
  4. What is the importance of fat (lipids) and water solubility with respect to the BBB?
  5. Use what you have learned to explain how the cells of the brain are protected by the BBB. Why do you think alcohol has such a rapid and extreme effect on behavior?

Review Questions/Answers

  • Sample answers to these questions will be provided upon request. Please send an email to teachers-requests@ck12.org to request sample answers.
  1. What are the three major divisions of the nervous system?
  2. In general, what does the nervous system do?
  3. List three aspects of the nervous system and brain you find remarkable. Explain why they are remarkable.
  4. How is the brain protected from damage?
  5. Why is wearing a bicycle helmet important?
  6. What substances does the blood-brain barrier not keep out? Why?
  7. Why can drugs or alcohol affect behavior so quickly?

Activity 1-1 Report: The Blood-Brain Barrier (BBB) (Student Reproducible)

1. Observe Test Tube A. Make a labeled drawing in color of the test tube and its contents.

a. Do the water and oil mix?

b. What happens when you shake the test tubes?

2. Observe Test Tube B. Make a labeled drawing of the test tube and its contents before and after adding the drops of blue food color. If the blue color is a water-soluble chemical, where would it go if it reached the brain in the bloodstream?

3. Observe Test Tube C. Make a labeled drawing of the test tube and its contents before and after adding the colored oil. If the colored oil is a fat-soluble chemical, where would it go if it reached the brain in the bloodstream?

4. a. Predictions for shaking Test Tube D for 10 seconds.

b. Results of shaking Test Tube D for 10 seconds.

c. Explain any differences between your predictions and your observed results.

d. If there are water-soluble and fat-soluble chemicals circulating in your blood, which is more likely to cross your BBB? Why?

5. a. Describe your results from the experiment with Test Tubes E and F.

b. How do these results differ from your observations on Test Tubes B and C?

c. Do you think it is easy for alcohol to cross the BBB?

6. What is the importance of fat (lipids) and water solubility with respect to the BBB?

7. Use what you have learned to explain how the cells of the brain are protected by the BBB. Why do you think alcohol has such a rapid and extreme effect on behavior?

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