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Advan. Physiol. Edu. 27: 87-88, 2003; doi:10.1152/advan.00062.2002
1043-4046/03 $5.00
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ADV PHYSIOL EDUC 27:87-88, 2003
© 2003 American Physiological Society

ILLUMINATIONS

A model for visualizing fluid handling by the gastrointestinal tract

David M. Lawson

Department of Physiology, Wayne State University School of Medicine, Detroit, MI 48201. dlawson{at}med.wayne.edu

Students often find models useful in learning or reviewing physiological concepts. As a result, we have developed a physical model of the gastrointestinal tract, which is used in the GI sections of our medical and graduate physiology courses to demonstrate ingested, secreted, reabsorbed, and excreted fluid volumes by the human digestive tract in a typical 24-h period.

The model was built on a four-tiered homemade shelving system (Fig. 1) assembled from lumber and other materials obtained from a local home improvement center (a list of materials and assembly instructions can be obtained upon request from the author). The tiered shelves make it possible for fluids to flow between the various containers by gravity when the model is in operation. The containers used for the model consisted of a 2-liter plastic soft-drink bottle filled with water (or water with food coloring added) to simulate the typical 24-h dietary fluid intake (A), a 2-liter clear glass bottle with an outlet containing 1.5 liters of water containing food coloring to simulate 24-h salivary secretion (B), a large funnel to simulate the oral cavity (C), a 5-liter clear glass bottle with an outlet to simulate the stomach containing 1 liter of colored water (the equivalent of the volume of gastric juice produced in 24 h (D), a 10- or l5-liter clear glass bottle or carboy with a side inlet to simulate the small intestine containing 1–2 liters of colored water (to simulate the 24-h production of intestinal secretions (E), a 2-liter bottle with outlet to simulate the liver containing the equivalent of the volume of bile produced in 24 h (0.5–1 liter of colored water (F), a 2-liter bottle with outlet to simulate the exocrine pancreas containing 1 liter of colored water (the equivalent of pancreatic juice produced in 24 h (G), a 4-liter bottle with outlet to simulate the colon (H), a 100-ml beaker (I), and a 3-liter bottle (J). The latter two containers are used to show, respectively, the volume of water normally excreted in feces in 24 h and the plasma volume. A small recirculating pump (K) is used to simulate "reabsorption" of fluid from intestine.



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  		FIG. 1 Assembled model for demonstrating the volumes of water processed by the human gastrointestinal tract in 24 h. See text for letter identification.

 
The model is operated by first identifying for the students what the containers represent and the volumes of fluid they contain. Then the contents of the "dietary liquids" bottle (A) are poured into the funnel (C). Next, the stopper is removed from the tubing from the "salivary gland" bottle (B) and the "saliva" is allowed to flow into the funnel. These fluids mix in the "stomach" (D), and the combined volume is allowed to drain into the "intestine" (E) by removing the he-mostat that clamps the connecting tubing. As the fluid from the "stomach" container flows into the "intestine" carboy, the hemostat clamping the tubing from the "liver" (F) and "pancreas" (G) containers is released, simulating the relaxation of the Sphincter of Oddi. As fluids flow into the "intestine" container, the "reabsorption" pump (K) is activated, pumping fluid from the "intestine" carboy into the "plasma volume" container (J). Water is also allowed to drain from the "intestine" carboy to the "colon" bottle (H). After 1–2 liters have drained, 100 ml of fluid are removed from the "colon" into a small beaker (I) to simulate the amount of water normally excreted in the feces. At this time, it is also possible to discuss the volumes of water that are excreted with common diarrhea or with more serious conditions like cholera. The explanation and operation of the model requires ~10–15 min. The only problems we have encountered are an occasional leaky connection and slow "reabsorption" flow from the pump. Students find this demonstration interesting and sometimes humorous (if leaks develop) as they learn and review fluid handling by the GI tract.


   Footnotes
 
SUBMITTING ILLUMINATIONS FOR REVIEW

As educators, we are continually designing new methods and procedures to enhance learning. During this process, good ideas are frequently generated and tested, but the extent of such activities may not be adequate for a full manuscript. Nonetheless, the ideas may be quite beneficial in improving the teaching and learning of physiology. Illuminations is a column designed to facilitate the sharing of these ideas (illuminations). The format of submissions is quite simple: a succinct description of about one or two double-spaced pages (less title and authorship) of something you have used for the classroom, teaching, lab, conference room, etc. You may include one or two simple figures or references. Submit ideas for inclusion in Illuminations directly to the Associate Editor in charge, Stephen DiCarlo (sdicarlo{at}med.wayne.edu). Back




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