Out of Breath - Lesson - www.TeachEngineering.org

The respiratory system consists of the trachea, bronchi, alveoli, and the lungs and is responsible for gas exchange between the environment and the body (delivery of oxygen from the lungs to the bloodstream and elimination of carbon dioxide from the bloodstream to the lungs). This system — along with the heart (located between the lungs; in fact, the left lung is slightly smaller to accommodate the heart) — is located in the thoracic cavity of the ribcage that provides protection. The diaphragm muscle separates this system from the abdominal cavity. See Figure 2 for an illustration of the chest cavity.

Drawing of the chest cavity (including the heart), with a magnified image of the alveoli off to the right side of the image.

Figure 2. The cardiovascular system.

Air first enters the body through the nose or mouth and then travels down the throat to the trachea (windpipe). Rings of cartilage protect the trachea from collapsing and subsequently blocking air from entering the lungs. The trachea then splits into two large tubes (one for each lung) called the right and left bronchi. The bronchi split into smaller bronchi and eventually become tiny bronchioles inside the lungs (see Figure 3). These bronchioles end in clusters of alveoli, which are tiny, thin-walled, air sacs that inflate as air enters the lungs and deflate as air exits (see Figure 4). The average, adult lung contains approximately 300 millions of these expandable sacs. Gas exchange then occurs between the alveoli and the pulmonary capillaries (tiny blood vessels) that lie within the alveoli walls. During inhalation, oxygen travels from the alveoli (high oxygen concentration) to the blood (lower oxygen concentration). Oxygen is then stored in the hemoglobin of the red blood cells to be delivered to the rest of the body. Conversely, during exhalation, carbon dioxide travels from the blood to the air.

Drawing of the bronchi, bronchial tree, and lungs with a magnified image of the alveoli off to the right side.

Figure 3. The respiratory system.

SEM image of alveoli with a magnified image of a single air sac below it.

Figure 4. Alveoli SEM image.

During inhalation, the diaphragm contracts downward and rib muscles pull upward causing air to fill the lungs (increases the volume of the thoracic cavity and decreases pressure in the lungs so the air will flow from the higher-pressure environment to lower-pressure area in the lungs). The diaphragm then relaxes, and the lungs contract which causes air to be pushed out from the lungs (exhalation).

Some common types of lung disease are:

Asthma: When respiratory muscles have to work harder due to the bronchioles constricting, which creates smaller airways (see Figure 5). It is a response to an allergen or other irritant (e.g., animal fur).

Drawing of a normal bronchus on the left compared to an asthmatic bronchus on the right.

Figure 5. Normal bronchus (left) and asthmatic bronchus (right).

Emphysema: When respiratory muscles have to work harder due to the fact that the lungs have become stiff with fibers and are less elastic in nature.
Bronchitis: When respiratory muscles have to work harder due to inflamed, narrow airways.
Pulmonary Edema: A slowing of the gas exchange due to a build up of fluid between the alveolus and pulmonary capillary (increases distance that the gases have to travel).
Pneumonia: Bacteria or virus that affects the membrane (pleura) that surrounds the lungs.
Lung Cancer: When malignant cells divide in the lung tissue, possibly invading nearby tissues or spreading through the blood stream; oftentimes caused by smoking. Figure 6 illustrates the presence of cancer in the lungs: the black areas are the lungs and the white patch on the right lung is cancer.

Image of the lungs (black masses) where the right lung (left side of image) has cancer (white mass).

Figure 6. Lung cancer.

Just Breathe - In this activity, students build a model lung to investigate the process of inhalation and exhalation. They discuss what happens during respiration and what might happen if the respiratory system were damaged.

Pre-Lesson Assessment

Discussion Question: Solicit, integrate and summarize student responses.

Ask the students if they know what happens inside their body when they breathe in and out. Do you breathe faster or slower when you are playing a sport? Why? (Answer: You breathe faster, because your body is using more oxygen.)

Post-Introduction Assessment

Voting: Ask a true/false question and have students vote by holding thumbs up for true and thumbs down for false. Count the votes and write the totals on the board. Give the right answer.

True or False: The lungs are part of the respiratory system. (Answer: True)
True or False: Our rib cage pushes in when we breathe in. (Answer: False. When we breathe in, our rib cage swings up and out, making more space for air to enter our lungs; when we breathe out, our rib cage moves down and back, pushing air from our lungs out our nose and mouth.)
True or False: An astronaut can breathe easily in space the same as they do on Earth. (Answer: False. An astronaut cannot breathe the same in space, because there is no air in space. The respiratory system needs oxygen and pressure to push the air in and out of the lungs.)
True or False: Engineers design devices to help astronauts breathe in space. (Answer: True. Engineers have designed systems to provide the right air pressure and oxygen amount during space flight and space exploration.)
True or False: Engineers work to help people who have respiratory problems (difficulty breathing properly). (Answer: True. Chemical engineers have created medicines for people with asthma, emphysema, bronchitis and pneumonia. Engineers have also designed an artificial lung to help people fight off infections. Lastly, engineers help design systems to give astronauts the right amount of air pressure and oxygen to survive in space.)

Lesson Summary Assessment

Send-a-Problem: Have students write their own questions about the respiratory system. Each student on a team creates a flashcard with a question on one side and the answer on the other. If the team cannot agree on an answer they should consult the teacher. Pass the flashcards to the next team. Each member of the team reads a flashcard and everyone attempts to answer it. If they are right, they pass the card on to another team. If they feel they have another correct answer, they can write it answer on the back of the flashcard as an alternative answer. Once all teams have tested themselves on all the flashcards, clarify any questions.

Thoughtful Questions: Ask the students the following extension questions about the respiratory system

Does the way you breathe change during space flight? (Answer: No, but your lung capacity decreases due to the fact that other internal organs shift upward in microgravity.)
Can people breathe underwater? (Answer: People can only breathe underwater if they take an air supply with them. Engineers have helped design air supply devices, such as diving tanks, to help people breathe in extreme conditions.)

BBC News, Heath, "Artificial lung breakthrough," April 26, 2001. www.bbc.co.uk/news Accessed May 23, 2006

Lujan, Barbara. and White, Ronald. National Space Biomedical Research Institute, Human Physiology in Space, Houston, TX: GPO, 1995. www.nsbri.org Accessed May 23, 2006

Short, Sr., Nicholas M. National Aeronautics and Space Administration, Information Sciences Branch, Goddard Space Flight Center, The Remote Sensing Tutorial (RST).

U.S. Department of Health and Human Services, Office on Women's Health, National Women's Health Information Center (NWHIC), GirlsHealth.gov, Body - Becoming a Woman, "Learn about your whole body - from your heart to your bones," March 2006.

U.S. Department of Health and Human Services, Office on Women's Health, National Women's Health Information Center (NWHIC), Lung Disease, March 2006.

U.S. National Cancer Institute's Surveillance, Epidemiology and End Results (SEER) Program, Bronchi, Bronchial Tree, and Lungs, "Bronchi and Bronchial Tree."