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Lesson: Breathe In, Breathe Out

Contributed by: Integrated Teaching and Learning Program, College of Engineering, University of Colorado at Boulder
Diagram shows nasal cavity, sinuses, trachea, lungs, bronchi, heart, pulmonary vessels and diaphragm superimposed on the body of a girl.
The human respiratory system.


Students are introduced to the respiratory system, the lungs and air. They learn about how the lungs and diaphragm work, how air pollution affects lungs and respiratory functions, some widespread respiratory problems, and how engineers help us stay healthy by designing machines and medicines that support respiratory health and function.

Engineering Connection

Engineering analysis or partial design

Some engineers work with doctors to find engineering solutions to problems affecting the human body and the respiratory system. Engineers use their knowledge of respiration, air flow, fluid flow and membranes to devise systems to provide functions of the respiratory system to patients when their respiratory system, or parts of it, fail. Examples include medicines and inhalers, pulmonary function testing and screening equipment (spirometers), and heart-lung bypass devices (artificial lungs).


  1. Pre-Req Knowledge
  2. Learning Objectives
  3. Introduction/Motivation
  4. Background
  5. Vocabulary
  6. Associated Activities
  7. Lesson Closure
  8. Assessment
  9. Extensions
  10. Multimedia
  11. References

Grade Level: 7 (4-7) Lessons in this Unit: 12345678910
Time Required: 20 minutes
Lesson Dependency :None
Keywords: air, bioengineering, biomedical, biomedical engineering, biotechnology, breathe, body, human, human body, gas exchange, lung, oxygen, pulmonary, respiratory, respiratory system, respiration, spirometer
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Related Curriculum

subject areas Biology
Life Science
curricular units Biomedical Engineering and the Human Body
activities Polluted Air = Polluted Lungs

Educational Standards :    

Does this curriculum meet my state's standards?       

Pre-Req Knowledge (Return to Contents)

Some basic knowledge of the parts of the human respiratory system.

Learning Objectives (Return to Contents)

After this lesson, students should be able to:
  • List several causes and effects of decreased respiratory system function.
  • Describe technologies that engineers have designed to improve the health and function of the respiratory system.

Introduction/Motivation (Return to Contents)

When was the last time you thought about your respiratory system? When was the last time you coughed, sneezed or hiccupped? Every time you do one of these things, it should remind you of your respiratory system. From where does a cough come? A sneeze? What about a hiccup? A cough is the way your respiratory system clears the airway. A sneeze is caused by an irritation in the upper airway. A hiccup is a spasm of the diaphragm. The respiratory system is an internal system that is constantly exposed to the outside environment. Every time we breathe in, we take in what is in the air around us, including dust, bacteria, pollen, smoke and chemicals. Our respiratory systems help us filter out these particles before they enter our bloodstreams.
Does the respiratory system always work? Many things we breathe in can harm and even destroy the respiratory system. People who suffer from asthma often cough and find it hard to breathe. Lung cancer, especially common among people who smoke, can kill people. Tuberculosis (TB), a disease caused by bacteria, can destroy a person's lungs. TB is highly contagious, and affects cats and other animals as well as people. Most people, at some point, experience minor and temporary respiratory problems in the form of a sore throat, cough or bronchitis.
Photo shows a man with his nose pinched closed breathing into a tube connected to a machine with a display and paper printout.
Figure 1. Engineers design spirometers to measure your lung capacity — how fast and how much air you breathe.
Asthma is experienced when the inside walls of your airways become swollen and sensitive. Then, if something irritating enters your airways, they narrow, restricting oxygen from reaching your lungs. In a severe asthma attack, the airways can close so much that your vital organs do not get enough oxygen. Chemical engineers design medicines and their delivery systems, such as inhalers, to help people breathe better. Some medicines are for quick-relief, to stop asthma symptoms when they happen and others are long-term control medicines, to prevent symptoms.
Lung transplants are necessary when lungs are too damaged to work anymore and no other alternative treatments exist. In 2005, about 3,500 people in the U.S. were waiting for lung transplants, and only 1,000 of them received transplants. Hospitals use machines designed by engineers that do the work of the heart and lungs, by pumping blood and exchanging oxygen outside the body to help a patient recover from a case of lung failure from infection or trauma. Engineers are working on devices that could filter and clean oxygen inside the body, similar to the way working lungs do. These artificial lungs would be small (about the size of a soda can) and implanted in patients'chests to help them stay alive longer while waiting for lung transplants.
To design machines and medicines to help people whose respiratory systems are not fully functioning, engineers must thoroughly understand the human respiratory process. Some biomedical, electrical and mechanical engineers develop pulmonary function testing and diagnostic equipment (spirometers, see Figure 1), as well as artificial lungs that help seriously ill patients breathe while fighting off infections.

Lesson Background & Concepts for Teachers (Return to Contents)

The Respiratory System

The respiratory system is an organ system in the body primarily used for gas exchange. In most four-legged animals, the respiratory system generally includes tubes, called the bronchi, which carry air to the lungs, where gas is exchanged. A diaphragm pulls air in and pushes it out.
In humans and other mammals, the respiratory system consists of the airways, the lungs and the respiratory muscles that move air into and out of the body (see Figure 2). In the alveoli of the lungs, oxygen and carbon dioxide molecules are exchanged between the gaseous environment in the lungs and the blood. The respiratory system facilitates the movement of oxygen to the blood (oxygenation), while removing carbon dioxide and other gaseous wastes from circulation.
The respiratory system provides energy to the body by delivering oxygen to the lungs, from where it travels through the blood to the cells. The respiratory system also removes waste by-products of respiration and various cell functions, such as carbon dioxide. The respiratory system is connected to the circulatory system.
Diagram shows and identifies nasal cavity, pharynx and larynx of upper respiratory tract, and trachea, primary bronchi and lungs of lower respiratory tract.
Figure 2. The human respiratory system's conducting passages, upper and lower.
Inhalation is driven primarily by the diaphragm. When the diaphragm contracts, the ribcage expands and the contents of the abdomen are moved downward. This movement results in a larger volume inside the chest cavity, which causes a decrease in pressure. As the pressure in the chest falls, air moves into the conducting zone, where it is filtered, warmed and humidified — all by different parts of the respiratory system — as it flows to the lungs. By contrast, exhalation is typically a passive process. The lungs have a natural elasticity, or ability to stretch. As the lungs recoil from the stretch of inhalation, air flows back out until the pressures in the chest and the atmosphere become equal.
After air inhalation, gas exchange occurs in the alveoli, which are the tiny sacs in the lungs at which gas exchange takes place. Aveoli walls are extremely thin and permeable to gases, so gases flow easily between them. The alveoli are lined with pulmonary capillaries, the walls of which are also thin enough to permit gas exchange. Oxygen diffuses from the air in the alveoli to the blood in the pulmonary capillaries. At the same time, carbon dioxide diffuses in the opposite direction, from the blood in the capillary to the air in the alveoli. At this point, the pulmonary blood is oxygen-rich, and the lungs are holding carbon dioxide. Exhalation follows, ridding the body of the carbon dioxide, and completing the respiration cycle.
See the Vocabulary/Definitions section for information on additional, important components of the respiratory system, and their functions.

Artificial Lungs

Currently, engineers are working to develop small artificial lungs that can be implanted into the chest. The intent is for this technology to efficiently carry on the gas exchange function of a person's lungs during recovery from injury or illness, or until donor lungs are available for transplantation. Hospitals currently use a technology called ECMO, or extracorporeal membrane oxygenation. ECMO machines take over the functions of the lungs and heart, pumping blood and exchanging carbon dioxide for oxygen in a machine outside the body. The drawbacks to using this external type of machine include the mechanical pumps, which may damage red blood cells. These new artificial lungs would use the heart as the pump and be implanted into the chest to eliminate some of the current problems. While these new technologies are not a long-term solution for severe lung damage, they may give patients enough support until donor lungs become available.

Vocabulary/Definitions (Return to Contents)

adenoids: Lymph tissues at the top of throat. The entire lymph system carries fluid to the body and aids it in resisting infection by filtering foreign matter (such as germs) and producing cells (called lymphocytes) to fight harmful germs. If adenoids become enlarged they may interfere with breathing and are sometimes removed.
alveoli: Very small air sacs that are the final place air goes when breathed in. Blood passes through capillaries that are embedded in the alveoli walls, taking up oxygen from the air and giving off carbon dioxide.
bioengineering: The use of artificial tissues, organs or organ components to replace damaged or absent parts of the body, such as artificial limbs and heart pacemakers. Source: The Oxford Pocket Dictionary of Current English, http://encyclopedia.com/doc/1O999-bioengineering.html
biomedical engineer: A person who blends traditional engineering techniques with the biological sciences and medicine to improve the quality of human health and life. Biomedical engineers design artificial body parts, medical devices, diagnostic tools, and medical treatment methods.
bronchial tubes: When the windpipe reaches the lungs it splits into two main tubes, one to each lung. The tubes divide again into each lobe of the lung, and then continue to divide even further.
bronchioles: The smallest subdivisions in the bronchial tubes. At the end of the bronchioles are air sacs, called alveoli.
cilia: Very small hairs that line the bronchial tubes. Their wave-like motion carries mucus up and out into the throat. The mucus catches and holds much of the dust, germs and other unwanted particulate materials that find their way into the lungs, and releases them from the body by coughing and sneezing.
diaphragm: A strong wall of muscle that, when moved downward, creates suction in the chest that draws in air and expands the lungs. The diaphragm separates the chest cavity from the abdominal cavity.
engineer: A person who applies his/her understanding of science and math to creating things for the benefit of humanity and our world.
epiglottis: A tissue flap at the entrance to the windpipe that closes during swallowing, preventing food or drink (destined for the esophagus and stomach) from entering the lower respiratory tract.
esophagus: The vessel that leads from the mouth and throat to the stomach.
lymph nodes: Small, rounded structures found against the walls of the bronchial tubes and windpipe. They produce disease-fighting white blood cells and filter out harmful microorganisms and toxins.
mouth: The secondary entrance of air into the respiratory system.
nose: The primary and preferred entrance of outside air into the respiratory system. The hairs inside the nose serve to clean the air of particulates before it enters the deeper parts of the respiratory system.
ribs: Bones that both support and protect the chest cavity and lungs.
sinuses: Hollow spaces in the bones of the head with small openings that connect them to the nose. The sinuses help regulate temperature and humidity of incoming air, as well as serving to lighten the bone structure of the head.
throat: The passage that collects outside air from the nose and mouth and moves it down toward the windpipe. Also called the pharynx.
tonsils: Almond-shaped lymph nodes in the wall of the throat. They fight unwanted germs and can become infected.
voice box: A structure at the top of the trachea (windpipe) that contains the vocal chords and is the source of voice sounds caused by moving air. Also called the larynx.
windpipe: The passage that leads from the throat to the lungs. Also called the trachea.

Associated Activities (Return to Contents)

  • Polluted Air = Polluted Lungs - Students use balloons, straws and plastic bottles to make model lungs that include diaphragms and chest cavities, enabling them to see how air moving in and out of the lungs coincides with diaphragm movement. Teams also design and create prototype face filters that could be worn to reduce the amount of air pollution entering the respiratory system.

Lesson Closure (Return to Contents)

The respiratory system is an incredibly important system in our bodies. Understanding its function is critical to keeping our bodies healthy and responsive to situations and medical problems that we encounter. Understanding how air pollution and contaminants in the air that we breathe directly affect the respiratory system and lungs is also critical in understanding how to protect and prolong the life and functioning of the respiratory system.
Engineers work with doctors to come up with medical testing and treatment solutions to issues affecting the respiratory system, as well as monitoring and improving the quality of the air that is inhaled by it. Many types of engineers contribute to projects that improve the health of people's respiratory systems. Chemical engineers design medicines that help people breathe better. Other engineers design the medicine delivery systems, whether they are inhalers, syringes or pills or capsules. Biomedical, electrical and mechanical engineers develop pulmonary function testing and screening equipment, as well as artificial lungs that help ill patients breathe and filter oxygen while fighting off infections.

Pre-Lesson Assessment

Think/Pair/Share: Have students ask and answer the following questions with a partner:
  • What does the respiratory system do? (Answer: Gas exchange.)
  • What different parts make up the respiratory system? (Answer: Mouth, nose, larynx, diaphragm, lungs, etc.)
  • What might make the respiratory system not work as well? (Answer: Constricted pathways, polluted air, less volume, etc.)

Post-Introduction Assessment

Scenario/Question: Provide students with the following scenario/question, asking them to write a brief and clear description, accurately using respiratory system terms:
  • You are a molecule of air outside of the body, just about to be inhaled. From the point-of-view of the air molecule, describe what happens to you as you enter the body's bloodstream. You may use a diagram, but support the diagram with detailed descriptions of what is happening. Describe in detail what each part of the respiratory system does to you after you enter the body. Make sure to include these parts of the respiratory system in the description: Nose, throat/epiglottis, larynx (voicebox), trachea (windpipe), bronchial tubes, cilia, diaphragm, alveoli, capillaries.

Lesson Summary Assessment

Discussion: If you were an engineer creating a set of artificial lungs, what design considerations would be important to think about? (With this open-ended design question, the teacher is looking for evidence that students are thinking about the parts of the respiratory system, its function, and what affects it. Example responses might include: Lungs should be able to stretch, lungs should be able to fit in the chest cavity, lungs should be able to carry out gas exchange, lungs should be supple, must know the person's health history, how much more the person might grow, location where the person lives and breathes, etc.)

Lesson Extension Activities (Return to Contents)

Have students research engineering advancements in artificial lungs. How has this technology increased the rate of survival of people who have damaged lungs?
Asthma is the leading serious chronic illness of U.S. children. Have students learn more about asthma, its symptoms and triggers. Most students know someone with asthma. Direct students to research the medicines and inhalers engineers have developed to help manage asthma attacks.
Lung disease is one of the top three diseases causing death in the U.S., and lung disease and respiratory problems are the leading cause of death of infants under the age of one. Have students learn more about lung disease, its causes, symptoms and treatments. Assign students to create an informational brochure for their school, family or community outlining the risks and what can be done to reduce one's chances of lung disease.

Additional Multimedia Support (Return to Contents)

See a good overall respiratory system diagram with parts identified and described (interactive flash presentation) at the American Lung Association's Search LungUSA website: http://www.lungusa.org/your-lungs/how-lungs-work/

Asthma. American Lung Association. Accessed December 16, 2008. http://www.lungusa.org/lung-disease/asthma/

Dictionary.com. Lexico Publishing Group, LLC. Accessed December 16, 2008. (Source of some vocabulary definitions, with some adaptation) http://www.dictionary.com

Downs, Martin F. Artificial Lung Closer to Clinical Trial. Reviewed November 25, 2002. WebMD, Inc. Accessed December 16, 2008. http://www.webmd.com/healthy-aging/features/artificial-lung-closer-to-clinical-trial

How Lungs Work, The Respiratory System. American Lung Association. Accessed November 3, 2010. (interactive flash presentation shows diagram and description of parts of human respiratory system, titled, "Would You Like to See How I Breathe?"; scroll down the page to find it) http://www.lungusa.org/your-lungs/how-lungs-work/

Lamb, Annette and Johnson, Larry. Respiratory System: The Basics. Last updated December 2001. 42eXplore. Accessed December 16, 2008. http://42explore.com/respsyst.htm

Marcus, Mary Brophy. Breakthroughs in Artificial Lungs Could Assist in Transplants. Updated January 30, 2008. USA Today. Accessed December 16, 2008. http://www.usatoday.com/news/health/2008-01-29-artificial-lungs_N.htm

Respiratory System. Last updated August 8, 2007. Wikipedia Free Online Encyclopedia. Accessed August 12, 2007. http://en.wikipedia.org/wiki/Respiratory_system

Rodriguez-Cruz, Edwin. Extracorporeal Membrane Oxygenation. Last updated June 14, 2006. eMedicine, WebMD, Inc. Accessed October 13, 2008. http://www.emedicine.com/ped/TOPIC2895.HTM


Jay Shah, Malinda Schaefer Zarske, Denise W. Carlson


© 2008 by Regents of the University of Colorado. This digital library content was developed by the Integrated Teaching and Learning Program under National Science Foundation GK-12 grant no. 0338326. However, these contents do not necessarily represent the policies of the National Science Foundation, and you should not assume endorsement by the federal government.

Supporting Program (Return to Contents)

Integrated Teaching and Learning Program, College of Engineering, University of Colorado at Boulder

Last Modified: April 24, 2014
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