Diffusion in the Respiratory System: Function & Process

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  • 0:00 What Is Diffusion?
  • 1:24 What Is the…
  • 2:17 Process of Gas Exchange
  • 3:10 Functions of Gas Exchange
  • 4:24 Lesson Summary
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Lesson Transcript
Instructor: Amanda Robb

Amanda holds a Masters in Science from Tufts Medical School in Cellular and Molecular Physiology. She has taught high school Biology and Physics for 8 years.

This lesson is on diffusion in the respiratory system. We'll define diffusion and the respiratory system, and then we'll cover how diffusion helps the respiratory system function in the body.

What Is Diffusion?

If you've ever had a cup of tea in the morning, you've probably watched the tea spread out as it hits the hot water. The tea starts in the tea bag, which is filled with tea leaves. Slowly, the tea seeps out into the water. As time passes, the once-clear water becomes homogeneously brown with the tea. Once the tea cools, you are free to enjoy and get your caffeine fix for the day. This process you see every morning with your tea is called diffusion. Diffusion is the process of something moving from high concentration to low concentration, and it happens in your body all the time and doesn't need energy to get started.

Think of diffusion like rolling a ball down hill. If you have a ball teetering on the edge of a hill, the ball will always roll downward, from a high to low elevation. Unless you push it up by exerting energy, it will never go up the hill by itself. Diffusion continues until equilibrium, or the point where everything is in balance, is reached. Think of your tea: It eventually becomes all the same color, dark brown, and stays that way. The tea has reached equilibrium at that point. Now that we're clear on diffusion, let's take a look at the respiratory system and how diffusion works there.

What Is the Respiratory System?

The respiratory system is a collection of organs and tissues that control gas exchange in the body. It's how we take in oxygen and exhale carbon dioxide. In our bodies, the respiratory system starts with the mouth and nose, where air enters the body. Next, the air travels through the trachea, or windpipe in the throat. After that, the trachea splits into tubes called the right and left bronchi. These tubes continue to branch and get smaller and smaller, like branches on a tree.

At the smallest branches of the bronchi, called bronchioles, there are little sacs known as alveoli, which are surrounded by tiny blood vessels called capillaries. Think of the alveoli like the leaves on the end of tree branches. In general, all branches lead to leaves, which is how the tree takes in and gives off gases.

Process of Gas Exchange

Our bodies all need oxygen to survive, but in the process of using oxygen, we also produce carbon dioxide, which is toxic. The body needs a way to get oxygen in and carbon dioxide out, which is through diffusion. When blood returns to your lungs from the body, it has a lot of carbon dioxide and little oxygen. The carbon dioxide concentration is much greater in your blood than the alveoli. So, by the rule of diffusion, the carbon dioxide moves from the blood to the alveoli, where it can be exhaled through the lungs.

The same thing happens with oxygen. Since blood returning to the lungs has lots of carbon dioxide and very little oxygen, there is more oxygen in the alveoli compared to the blood. Oxygen diffuses into the blood from the alveoli.

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