Teaching in the Laboratory

How does a hopping kangaroo breathe?

Published Online:https://doi.org/10.1152/advan.00050.2010

Abstract

We developed a model to demonstrate how a hopping kangaroo breathes. Interestingly, a kangaroo uses less energy to breathe while hopping than while standing still. This occurs, in part, because rather than using muscle power to move air into and out of the lungs, air is pulled into (inspiration) and pushed out of (expiration) the lungs as the abdominal organs “flop” within the kangaroo's body. Specifically, as the kangaroo hops upward, the abdominal organs lag behind, and the insertion of the diaphragm is pulled toward its origin, flattening the dome and increasing the vertical dimension of the thoracic cavity (the thoracic cavity and lungs enlarge). Increasing the volume of the thoracic cavity reduces alveolar pressure below atmospheric pressure (barometric pressure), and air moves into the alveoli by bulk flow. In contrast, the impact of the organs against the diaphragm at each landing causes expiration. Specifically, upon landing, the abdominal organs flop into the diaphragm, causing it to return to its dome shape and decreasing the vertical dimension of the thoracic cavity. This compresses the alveolar gas volume and elevates alveolar pressure above barometric pressure, so air is expelled. To demonstrate this phenomenon, the plunger of a syringe model of the respiratory system was inserted through a compression spring. Holding the syringe and pressing the plunger firmly against a hard surface expels air from the lungs (the balloon within the syringe deflates) and compresses the spring. This models the kangaroo landing after a hop forward. Subsequently, the compression spring provides the energy for the “kangaroo” to “hop” forward upon the release of the syringe, and air enters the lungs (the balloon within the syringe inflates). The model accurately reflects how a hopping kangaroo breathes. A model was chosen to demonstrate this phenomenon because models engage and inspire students as well as significantly enhance student understanding.

teachers often overrate the importance of their content knowledge and underrate the importance of their pedagogical knowledge (15). However, being an effective teacher requires more than knowing one's own discipline. Being an effective teacher also requires understanding how people learn. In this context, how we teach (process) is more important than what we teach (content) (12). Process is more important than content because students forget much of the content they memorize. Thus, teachers must stop trying to teach students the entire context they will need to know. Rather, teachers must focus on students developing an interest and love for lifelong learning. Developing an interest and love for lifelong learning is critical because unless students are intrinsically motivated to learn our efforts are pointless. Once students are intrinsically motivated to learn, there are countless resources available to learn more about a subject. Thus, inspiring and motivating students is far more important for long-term success than delivering information (13). Therefore, teachers must create a joy, an excitement, and a love for learning. Teachers must make learning fun, because this will result in students who are motivated to learn and therefore impatient to run home, to study and contemplate, and to really learn (23, 26).

To inspire and motivate students and to help students develop an interest and love for lifelong learning, we developed a simple, inexpensive, and easy to build model that demonstrates how a hopping kangaroo breathes. The kangaroo is interesting and inspires a desire to learn because, amazingly, a kangaroo uses less energy to breathe while hopping than while standing still. This simple and inexpensive model also encourages research-oriented learning (8, 9, 1722, 30, 3234) because physical models relate the unknown to the familiar and help to explain complex ideas by promoting logic, reasoning, and creativity. Finally, models encourage a new perspective on information gathering by providing a minds-on, see-touch interaction to supplement new information processing while promoting curiosity, healthy skepticism, objectivity, and the use of scientific reasoning (12).

METHODS

The following are directions for the construction of a simple, inexpensive, and easy to build model to demonstrate how a hopping kangaroo breathes (Fig. 1). The materials required to build the model are shown in Fig. 2. In this model, the syringe (Fig. 2, no. 6) represents the kangaroo's body (thorax and abdomen), and the plunger of the syringe is the diaphragm and abdominal viscera. The compression spring (Fig. 2, no. 7) provides an important linkage coupling the movement of the kangaroo with the movement of the plunger within the syringe. Interestingly, a kangaroo uses less energy to breathe while hopping than while standing still. This occurs, in part, because rather than using muscle power to move air into and out of the lungs, air is pulled into (inspiration) and pushed out (expiration) of the lungs as the abdominal organs “flop” within the kangaroo's body. Specifically, as the kangaroo hops upward, the abdominal organs lag behind, and the insertion of the diaphragm is pulled toward its origin, flattening the dome and increasing the vertical dimension of the thoracic cavity (the thoracic cavity and lungs enlarge). Increasing the volume of the thoracic cavity reduces alveolar pressure (PA) below atmospheric pressure [barometric pressure (PB)], and air moves into the alveoli by bulk flow. In contrast, the impact of the organs against the diaphragm at each landing causes expiration. Specifically, upon landing, the abdominal organs flop into the diaphragm, causing it to return to its dome shape and decreasing the vertical dimension of the thoracic cavity. This compresses the alveolar gas volume and elevates PA above PB, so air is expelled (expired).

Fig. 1.

Fig. 1.Simple, inexpensive, and easy to build model to demonstrate how a hopping kangaroo breathes.


Fig. 2.

Fig. 2.Materials required to build the model. 1, Becton-Dickinson catheter tip syringe; 2, three-way valve, 3, 4-cm tubing (6-mm outer diameter × 3-mm inner diameter); 4, 4-in. balloon; 5, 15-cm tubing; 6 and 6a, syringe and syringe plunger; 7, compression spring; 8, bolt; 9, nuts; 10, straight edges of a wire clothes hanger.


Respiratory System

Step 1.

To build the respiratory system, drill a 3-mm hole next to the luer in the 60-ml Becton-Dickinson catheter tip syringe body (Fig. 2, no. 1, arrow) and insert the three-way valve (Fig. 2, no. 2) into the hole. Secure the three-way valve in place with glue from a glue gun (Fig. 3, no. 2). The valve will allow you to purge air from the syringe as you insert the balloon (lung) and “set up” the system (see below).

Fig. 3.

Fig. 3.Completed respiratory system. 2, Three-way valve; 3, 4-cm tubing (6-mm outer diameter × 3-mm inner diameter) secured in place with glue from a glue gun; 6, syringe plunger; 7, compression spring; 8, bolt; 9, nuts.


Step 2.

Place one of the 4-cm-long pieces of tubing (6-mm outer diameter × 3-mm inner diameter; Fig. 2, no. 3) perpendicular to the syringe, between the luer and the syringe body (Fig. 3, no. 3). Secure the tubing in place with glue from a glue gun.

Step 3.

Place the other 4-cm-long piece of tubing (6-mm outer diameter × 3-mm inner diameter; Fig. 2, no. 3) perpendicular to the syringe, between the hand support and the base of the syringe body (Fig. 3, no. 3). Secure the tubing in place with glue from a glue gun.

Step 4.

Tie (with suture) the 4-in. balloon (“lung;” Fig. 2, no. 4) tightly to the 15-cm piece of tubing (Fig. 2, no. 5). Be certain there are no air leaks between the balloon and the tubing. To check for leaks, pump air into the balloon with a syringe connected to the opposite end of the tubing.

Step 5.

Remove the plunger from the syringe (Fig. 2, no. 6) and put the tubing with the balloon attached (Fig. 2, nos. 4 and 5) into the syringe body. Advance the tubing through the luer. From the outside of the syringe, pull the tubing and balloon into the luer (Fig. 3). To avoid air loss from the syringe through the luer, seal the luer with glue from a glue gun (Fig. 3).

Step 6.

Drill a 5-mm hole through the syringe plunger (Fig. 2, no. 6a) ∼7 cm from the end (the end where you hold the plunger with your hands).

Step 7.

Place the syringe plunger into the syringe. Slide the compression spring (Figs. 2 and 3, no. 7) over the plunger (Figs. 2 and 3, no. 6).

Step 8.

Finally, using the hole in the syringe plunger made in step 6, secure the compression spring in place using the bolt (Figs. 2 and 3, no. 8) and nuts (Figs. 2 and 3, no. 9). This completes construction of the respiratory system (Fig. 3).

Kangaroo

Step 1.

Use the template (Fig. 4) downloaded from the following site: http://www.writing-for-children.com/kangathingstodo.html [artist: Peter Taylor (35a)].

Fig. 4.

Fig. 4.Template used to construct the kangaroo. The template was downloaded from the following site: http://www.writing-for-children.com/kangathingstodo.html [artist: Peter Taylor (35a)].


Step 2.

The template (Fig. 4) was used to build a standing model of a kangaroo. The size can be adapted to any size syringe by simply enlarging or diminishing the design.

Step 3.

Fold construction paper in half so that the desired design size of the half-kangaroo will fit on each side of the crease. The back of the half-kangaroo should be positioned along the crease.

Step 4.

Cut the construction paper following only the bold lines of the template outline. After cutting the template and unfolding the kangaroo model, the dashed lines on the design should be used to guide the folding of the tail, head, neck, face, and ears of the unfolded kangaroo. The tail should be folded toward the back, while the head should be folded pointing to the front of the kangaroo. For the ears, neck, and face, the folding should be done only in the middle of each structure to simply give it a curved look.

Connecting the Respiratory System to the Kangaroo

Step 1.

Place the two segments of a cut hanger (Fig. 2, no. 10), through the 4-cm-long pieces of tubing on the respiratory system (Fig. 3, no. 3). Now, “hang” the pieces of hanger on the forelimbs and hindlimbs of the kangaroo (Fig. 1).

Step 2.

The three-way valve (Fig. 3, no. 2) is used to set the initial (at rest) balloon volume since it allows us to control the pressure within the “pleural space.” Once the lung volume has been set at the desired level, the valve should be closed for the model to work properly.

RESULTS

To test this model, hold the syringe and press the plunger firmly against a hard surface to compress the compression spring. Air will exit the lungs (i.e., the balloon will deflate). This models the kangaroo landing after a hop forward. Specifically, this models the impact of the organs against the diaphragm at each landing, causing expiration. That is, upon landing the abdominal organs flop into the diaphragm, causing it to return to its dome shape and decreasing the vertical dimension of the thoracic cavity. This compresses the alveolar gas volume and elevates PA above PB, so air is expelled (expiration).

Next, release the syringe, and the compression spring will provide the energy for the “kangaroo” to “hop” forward, and air will enter the lungs (i.e., the balloon will expand). Specifically, as the kangaroo hops upward, the abdominal organs lag behind, and the insertion of the diaphragm is pulled toward its origin, flattening the dome and increasing the vertical dimension of the thoracic cavity (the thoracic cavity and lungs enlarge). Increasing the volume of the thoracic cavity reduces PA below atmospheric pressure (PB), and air moves into the alveoli by bulk flow (inspiration). In this context, the model accurately reflects how a hopping kangaroo moves air into and out of the lungs while using less energy to breathe while hopping than while standing still.

DISCUSSION

This simple, inexpensive, and easy to build model enabled us to demonstrate how a hopping kangaroo breathes (moves air into and out of the lungs). Using this model of the hopping kangaroo, in conjunction with several other simple, inexpensive, and easy to build models of physiological and pathological respiratory mechanics (8, 10, 12, 16, 19, 21, 22, 34), will engage, inspire, and motivate students because the models create a joy, excitement, and love for learning and make learning fun. Students, in our opinion, will appreciate building and working with these models, and, importantly, the models will be helpful to their understanding of respiratory mechanics. More importantly, the models promote curiosity, skepticism, objectivity, and scientific reasoning, which are fundamental attributes to the practice of medicine. Furthermore, these attributes should permeate the entire medical education continuum (2a, 12). In this context, “the true value of a teacher is determined not by what he knows, nor by his ability to impart what he knows, but by his ability to stimulate in others the desire to know” [Prof. Robert Lee Madison (1867–1954), Founder of Western Carolina University]. Therefore, rather than telling students what we know, we should show students how we learn, because showing students how we learn is inspiring, engaging, and motivating. When we are successful with this approach, we will have students who really learn and are able to solve novel problems. Models encourage these attributes (12) as we observed students engaged in the construction and testing of the model and believe that these efforts inspired student for future independent learning.

The American Association for the Advancement of Science (2) strongly recommends that “science be taught as science is practiced” because the traditional “lecture-then-test” format and accompanying “cookbook” laboratories are falling short of their educational goals (14). The American Association for the Advancement of Science encourages a transformation from instructor-led courses to dynamic student-centered experiences that engage students in research-oriented learning (27, 36).

Model building and manipulation engages students in research-oriented learning and is consistent with the nature of scientific inquiry (12). Specifically, an essential part of scientific inquiry is collaboration (1). Importantly, model building and manipulation provide opportunities for collaboration with faculty and peers. Furthermore, models are structured around complex problems that are rooted in situations that the learner is likely to encounter in the real world. Real-world problems motivate deep conceptual learning (e.g., when the learner extends what has been learned in one context to new contexts and applies the new information to solve novel problems). Students work collaboratively to build and manipulate the model, gathering information, learning from it, and finding solutions.

Models are also an effective teaching approach based on Ausubel's cognitive learning theory (3–5) that strongly encourages the construction of concepts and relationships. Ausubel's theory implies that the most important factor that influences learning is what the student already knows. The student must consciously and explicitly link new information to concepts they already know. In this way, students can identify new concepts and link them to existing concepts. This is critical because concepts do not exist in isolation, and each concept depends on its relationship to many others for meaning. Models are physical representations in which students construct meaningful relationships between concepts. Model building and manipulation actively engages students in searching for relationships between their existing knowledge and new knowledge.

Student engagement in the learning process is also facilitated by multiple sensory inputs (35). Models allow teachers to combine multiple sensory stimuli from reading the instructions, hearing directions from peers, and building and testing the model (25). This multiple-input experience encourages exploration, discovery, and inquiry into complex processes while accommodating a wide range of learning styles (6, 7, 11, 24). For example, models foster long-term learning by allowing students to see processes in three dimensions and to see how components move in ways that board sketches or two-dimensional pictures that jump between steps simply cannot replicate. The value of models may be associated with the dual-coding theory (28, 29), which suggests that long-term memory retention is facilitated by a combination of verbal and visual clues.

Conclusions

In summary, it is well known that many mammals, including humans, synchronize respiration with limb movement during locomotion. In contrast, the hopping kangaroo synchronizes respiration with whole body movement. We created a simple, inexpensive, and easy to build model to demonstrate this coupling. Using this model, we observed engaged and inspired students because the model created a joy, excitement, and love for learning and made learning fun. The students appreciated building and working with the model. In addition, the students appreciated the model and stated that it was helpful for their understanding.

DISCLOSURES

No conflicts of interest, financial or otherwise, are declared by the author(s).

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AUTHOR NOTES

  • Address for reprint requests and other correspondence: S. E. DiCarlo, Wayne State Univ. School of Medicine, 540 E. Canfield Ave., Detroit, MI 48201 (e-mail: ).