One of my student groups came up with an excellent way of presenting the organs of the digestive system in Biology class. They drew an outline of a person on the board and then had students in the audience stick drawings of the different organs onto the outline.
What worked particularly well was that they’d have someone from the class pin on the organ, and then they’d talk about it. This gave the presentation a nice rhythm, with a little break between each item.
In his critique of research on the beneficial-bacteria storing role of the appendix, PZ Myers includes an excellent overview of the digestive system.
When you eat something, it first goes into the stomach, where it’s treated to an acid bath, some enzymes, and a lot of muscular churning to break it up. Then it’s squirted into the small intestine, where the acids are first neutralized and more enzymes are tossed onto the watery, mushy soup that the food has been rendered down into, called chyme. The primary job of the small intestine is to suck all the nutrients out of the chyme and pass them on to the circulatory system.
Once as much of the good stuff has been leeched out of the chyme as your system can do, the soup is passed on to the large intestine …. This stuff is still very watery — if you’ve ever experienced diarrhea, that’s what it is at this point. The primary job of the large intestine is to resorb water from the waste, condensing it down into the thick, pasty glop we all know and love as excrement. The large intestine is basically the sewage treatment plant here.
The appendix has long been supposed to be a vestigial, useless organ. But a 2007 study suggests that it might have had — and may still have in many developing countries — an important role in digestion. It may provide a refuge for helpful, commensal bacteria to repopulate our guts after we purge when we get sick (Bollinger et al., 2007):
The organs of the lower digestive system. The appendix is located in the lower left, near where the small and large intestines meet. Image from Wikipedia.
… the human appendix is well suited as a “safe house” for commensal bacteria, providing support for bacterial growth and potentially facilitating re-inoculation of the colon in the event that the contents of the intestinal tract are purged following exposure to a pathogen.
The shape of the appendix is perfectly suited as a sanctuary for bacteria: Its narrow opening prevents an influx of the intestinal contents, and it’s situated inaccessibly outside the main flow of the fecal stream.
Proper respect for other living things requires us to minimize the waste we produce, and learn from the creatures we eat.
First off, three cheers for Viet Hoa, the Vietnamese food market on Cleveland Ave in Memphis. I’ve been searching for a source of fresh, uneviscerated, marine fish in this mid-continental city for quite a while, and I’ve finally found them. The market was the source of the subjects of an excellent anatomy lesson, and a delicious dinner.
I’d grabbed three fish, and a few goodies, and packed them on ice on the day before our trip. The large red snapper was a little pricey because it was fairly big, but I knew it would be quite tasty and I was hoping the internal organs would be big and clearly visible. The milk fish was an unknown, but it was big and cheap so worth experimenting on. The last fish was the smallest, and I’m not quite sure what kind it is, except that it’s marine. I’d tried one at home the previous week and found that while it had an excellent taste, the internal bits were on the small side.
Red Snapper
On the first night of the immersion I started with the biggest fish, the red snapper, with everyone around the table. I’m happy to say that all my students were there for the lesson, facing the table, even the more vegetarian minded. I’ve always believed that there is a certain, necessary, ethic to knowing where your food comes from, and what went into preparing it for you. If you’re going to eat meat, you should be able to spare a moment to think about the animal.
Small intestines are very long (and stretchy).
The digestive system was the easiest to identify and trace. The mouth and anus are pretty obvious on the outside. After cutting through the skin of the belly, you can follow the intestines from the anus all the way to the stomach. The intestines are quite long.
Shrimp-like stomach contents.
We found two partially digested, shrimp-like creatures in the stomach of the red snapper.
From the other end of the digestive system, once you get all the contents out of the body cavity, you can stick a probe through the mouth (watch out for sharp teeth) down through the esophagus to the stomach.
Pulling back the gills, you can see all the way through to the mouth. One student noticed how bright red the gills were, so we talked about oxygenation of blood and compared the fish’s gills to the human respiratory system.
Finally, I laid the fish on a bed of thinly sliced onions, surrounded it with wedges of tomato (seeded), covered it with lemon slices, dribbled a tablespoon of olive oil on top, and forgot to add the cup of white wine (which we did not seem to have on hand for some reason) and the bay leaf. It was a big fish so we ended up baking it for about 40 minutes at 400 degrees Fahrenheit.
Then we ate it. I say we, but it really was just a couple of students and myself who did most of the eating, although I believe I convinced everyone to at least try it. Of the more serious students of anatomy, the eyeballs were highly prized; with only three fish we did not have enough to go around.
Dinner is served.
By the time we were done with dinner the skeletal system was very nicely exposed.
The Other Fish
Opening the body cavity of the Milk fish.
A couple of my students did the honors of cleaning the other two fish. With its large organs, the milk fish was an excellent subject for dissection, but it was not particularly palatable. We did however find the gall bladder.
The breached gall bladder is on the lower right of the picture.
Even the smallest fish proved a worthwhile subject for the more patient student.
Up to the knuckles in fish.
Instead of eating the rather unappetizing, baked milk fish I combined it in a soup with some clams I’d picked up from Viet Hoa. I’d grabbed the clams so we compare modern bivalve shells to the cretaceous ones we’d find at Coon Creek. A bit of boiling with a few herbs, made for an excellent broth the following night.
In Summary
Cleaning fish for an anatomy lesson worked very well. As we excavated each internal organ, we could talk about what it did, why the fish needed it, and what was its analogue in humans. And, in the end, they made for a couple excellent meals.
P.S. – From the Gulf Coast Research Lab’s Marine Education Center, here’s a reference image for a perch dissection.
