Breathe In, Breathe Out - Lesson - www.TeachEngineering.org

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.

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.)