Functioning Lung Model


The mechanisms involved in human breathing should not be confused with cellular respiration. Visualizing the multiple muscle contractions involved in human breathing can be made easier with the help of a functioning teaching model. The general principle of air pressure differentials can be illustrated with this model.


  • Differential air pressure

  • Inhalation
  • Exhalation


Flinn Functioning Lung Model
Rubber band
Rubber dam with nut and bolt assembly

Safety Precautions

The latex (rubber dams) may be an allergen for some individuals. Exercise caution when pushing and pulling the rubber dam—not to do either too fast or hard causing it to tear.

Prelab Preparation

  1. Place the rubber dam over the opening of the bottle with the nut and bolt centered. The double nut should be on the outside of the model.
  2. Secure the rubber dam to the bottle opening by placing the rubber band over the rubber dam and around the rim of the bottle. Note: It may help to tape the rubber dam in place until it is secure with the rubber band, then remove the tape.
{10149_Preparation_Figure_1_Key parts of working lung model and represented anatomical structures}


Operate the lung model by alternately:

  1. Pushing in on the rubber dam material—simulating the relaxation of the diaphragm and causing expiration.
  2. Pulling down on the rubber dam material—simulating the contraction of the diaphragm causing inspiration.

Teacher Tips

  • As with any model, this model has its limitations. The real breathing mechanism as described in the discussion section points out the multiple contractions involved in breathing. Be sure students realize that even though this model is fun to operate and does illustrate the general principle of breathing, it does not show all the muscles involved in breathing.

  • After considering the mechanics of breathing, you might want to consider other topics of interest to students such as lung capacity, breathing rates and other breathing related activities. The Flinn student laboratory kit, Exercise, CO2 and Respirtion (Catalog No. FB1975) is a great activity for exploring the complex biofeedback mechanism by which the body uses CO2 and pH to regulate breathing.

Correlation to Next Generation Science Standards (NGSS)

Science & Engineering Practices

Developing and using models
Planning and carrying out investigations
Engaging in argument from evidence
Obtaining, evaluation, and communicating information

Disciplinary Core Ideas

MS-LS1.A: Structure and Function
HS-LS1.A: Structure and Function

Crosscutting Concepts

Stability and change
Structure and function
Systems and system models
Cause and effect

Performance Expectations

HS-LS1-2. Develop and use a model to illustrate the hierarchical organization of interacting systems that provide specific functions within multicellular organisms.
HS-LS1-3. Plan and conduct an investigation to provide evidence that feedback mechanisms maintain homeostasis.
MS-LS1-3. Use argument supported by evidence for how the body is a system of interacting subsystems composed of groups of cells.


The human breathing mechanism is in principle a simple concept. The nervous/muscular coordination, however, is complex. The basic principle is that muscular contractions alter the size of the internal chest cavity and create an air pressure differential between the inside of the chest cavity and the atmospheric air pressure outside the body. When the atmospheric air pressure outside the body is greater than inside the lungs, air enters the lungs. When the pressure is greater inside the lungs than outside the body, air leaves the lungs.

Basically two sets of muscles are involved in breathing. Intercostal muscles between the ribs and certain thoracic muscles can contract and relax, resulting in the raising and lowering of the rib cage. The contraction of the rib cage muscles causes the rib cage to be raised and the chest cavity to enlarge. (See Figure 2A—Inspiration.) While this is happening, the diaphragm (a very strong muscle) simultaneously contracts. This contraction lowers the diaphragm making the internal chest cavity even larger. Because of this chest cavity expansion, the air pressure inside the chest cavity is reduced and becomes less than the outside atmospheric pressure which causes air to rush into the lungs. These muscle contractions are alternately followed by a relaxation of the diaphragm and the rib cage muscles resulting in a decrease in the chest cavity size and an increase in air pressure inside the lung cavity. This increased pressure results in air being expelled from the lungs. (See Figure 2B—Expiration.)

  1. Inspiration—diaphragm and chest muscles are contracted, raising the rib cage and causing increased volume and decreased air pressure

  1. Expiration—diaphragm and chest muscles are relaxed, lowering the rib cage and causing decreased volume and increased air pressure.

In summary, changes in the size of the chest cavity affect the air pressure in the lungs. When the chest expands, the pressure within the chest falls. Because of this reduced air pressure, air is forced in from the outside, where it is under greater atmospheric pressure. When the chest cavity is reduced, the internal pressure becomes greater than the atmospheric pressure and air is forced out of the breathing passages. The autonomically controlled, rhythmic increase and decrease in the chest cavity’s volume is the mechanical “pump” driving air into and out of the lungs.

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