How Do Digestive Systems and Organs Vary In Size Relative To Body Length and Diet?
by Olivier Vallez
Introduction
    Throughout the world, people are obsessed with nutrition. Some people want to lose weight, some want to gain weight, others want more energy, better skin, longer life, etc. As a result, the ability of the body to digest different foods becomes an issue of concern. It is that concern that prompted me to investigate the differences in digestive systems that are equipped to digest only vegetables, only meat, or both.

    I hypothesized that the carnivorous digestive organs would be larger, and the herbivorous organs would be smaller. I figured that since meat has more calories from fat, which is hard to break down in human digestive systems, a system designed for the constant digestion of fats would be larger.

Methods and Materials
    Unfortunately, Mr. Reiblein would not have been too thrilled if I had asked for a cadaver, so I had to settle for small animals. For a carnivore, a cat; for a herbivore, a rabbit; and for an omnivore, a rat. I was given a dissection kit, including a scalpel, tweezers, probes, pins, and a dissecting pan. I added to that my ruler and a box of disposable surgical gloves, then I was in business.

    For each animal, the following process was repeated. I first measured the body length of the animal, tail not inclusive, and recorded it in centimeters. The first incision was made from the throat, down the middle of the body, to the genital area. Next, I made perpendicular incisions that were tangent at both ends of the first incision. Thus, the incisions formed an ³I² down the underside of the animalıs torso. The flaps of skin were pulled apart, exposing the animals innards. the small and large intestines were immediately visible, so those are what I removed first. By severing the large intestine at the rectum, doing the same at the connecting point between the stomach and small intestine, I removed the intestines from the body. The absence of the intestines exposed the stomach. I severed the stomach at the connecting point between it and the esophagus, thus removing the stomach. Dismembering the esophagus was a little bit more work. In order to reach the esophagus, I had to remove the heart and lungs of the animals. Unfortunately, the heart has many connecting tubes that had to be severed with care not to damage any of the surrounding tissues. Once the heart and lungs was removed, I severed the esophagus as close to the throat as possible, then removed it from the body.

    After all of the digestive organs were collected, I measured them by holding the intestines suspended in the air, and putting a ruler next to them. I recorded each measurement for each organ, then combined the measurements to formulate the length of the entire digestive system. The stomach was the only exception to this rule for it was measured three times - length, width, and depth. Thus, the stomach was measured both for length and for volume. Each measurement was then divided by the body length of the animal, and the numbers were compared and contrasted.

Results
    The results almost completely disproved my hypothesis. Proportional to body length, the rabbitıs digestive system was twice as long as the catıs, and the ratıs was even longer than the catıs. Furthermore, when the measurements are compared without relativity to body length (in other words, at face value), The rabbitıs digestive system is more than twice as long as the ratıs which is about 11 centimeters longer than the catıs. So even though the cat is nearly twice as big as the rat in body length, it still has a smaller digestive system.The data is presented more clearly in the attached table.
Discussion
    As a result of this experiment, my own personal perspective of diet and nutrition has changed. I was always under the assumption that meat was harder to digest than vegetables and starches, so I figured that a healthier diet would consist of less meat. However, the results of this experiment show that the process of digesting vegetables can indeed be a longer, more tedious one.

    There are, however, a few things that are left to be questioned in this experiment. Perhaps the most important and obvious glitch in this experiment is the lack of similarity between the three animals. While it is true that their diets and digestive systems differ, so do their respiratory systems, their natural habitats, etc. The structure of their digestive systems may be a result of something other than just their diets. Subsequently, the data collected in this experiment does not clearly define the relationship between an organismıs diet and its digestive organs.

    The format of the experiment also lends itself to experimental errors. Perhaps the most significant of these errors is the inability to take accurate measurements of some of the digestive organs. Specifically, the small and large intestines, since they are naturally in a coil, do not completely straighten. Consequently, some of the measurements are not quite correct. Fortunately, in this experiment, there was no doubt that the rabbit had the largest digestive organs; however, the comparison between the rat and the cat was closer, and the final data might have been different had the measurements been more accurate. Also, the abundance of bones and other such obstacles in both the throat and rectal areas of all three animals prevented me from removing the entire esophagus and large intestine. Thus, for animals such as the rabbit and cat, whose rectal and throat areas were larger than the ratıs, this meant more length lost in the measurements. Another factor was the volume of the digestive organs. The catıs intestines were so much thicker than those of the cat or rabbit, that they may not need the extra length that the other two animalıs organs have; or, perhaps there is some enzyme that the cat possesses that aids in the breakdown of meats and fats. If time allowed, I would have done more research into such questions, as well as taken diametric measurements of the organs.

    After conducting this experiment, I have not been able to draw any certain conclusions about the effect of diet on digestive organ size. I feel that to formulate a conclusion at this time would be unfair to the dignity of the experiment and would not resolve any of the issues that prompted it. I have, however, formed a theory that might explain the results of this experiment - the effect that an animalıs diet has on its digestive system probably has more to do with the chemicals and enzymes dispersed within the organs to help digestion than it does with the size of the organs.

Conclusion
    The obvious length and thickness differences between the ratıs, the catıs, and the rabbitıs digestive systems has lead me to theorize that the relationship between diet and digestive system goes beyond just organ size, to something more subtle, perhaps chemical. I believe that each organism contains varying enzymes that are specific to the digestive needs of the particular animal.

    In order to produce more accurate and conclusive data, I would suggest library research, as well as chemical testing of the digestive organs. I would also advise someone conducting a similar experiment to attempt to find a more accurate system for measuring the organs. Also, if time and supply permitted, I would advise him or her to conduct more than one trial. Hopefully, by increasing the number of trials, and increasing the accuracy and subsequently relevancy of the data, the results of the experiment could be more conclusive than mine.

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