An important part of anatomy study is the excretory system, which cleanses the body of wastes. Incorporating the large and small intestines and the kidneys, it is often considered the final stage of the digestive system. Discussion of the excretory system is likely to provoke some giggles among middle-school students, but teachers who approach the subject with interesting, hands-on activities--and a sense of humour--can succeed in teaching about this essential system.
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Take a Walk
Vivian Lee Ward, a teacher with National Health Museum, developed a walking tour through the digestive system, in which students carry an index card--symbolising a piece of food--through a series of stations representing the various parts of the digestive system. You could begin this "Walk through the Gut" with the "gut" itself, or include the excretory organs as part of the overall digestive system. At each station, students follow directions to "digest" their card ("food") by, for instance, tearing the card into smaller and smaller pieces or leaving corners of it behind to represent the nutrients that are removed from food waste.
If you'd like to combine your anatomy lessons with a publicity event, arrange for a visit from a giant-sized colon; the Prevent Cancer Foundation, for instance, offers "Super Colon." A Super Colon visit would be a chance for your school to involve parents and the wider community; coordinate plans and publicity with the school administration and parent-teacher organisation. Students will rarely otherwise have the chance to see inside a colon.
Simulate the System
Use household items and simple chemicals to simulate the various parts of the excretory system. For instance, unspool string or yarn to show students how long the large and small intestines are. Tint water with food colouring and challenge students to filter out the colour using paper towels, coffee filters, fish tank charcoal or household sponges. (Would it be brave--or foolish--to colour the water yellow?) Scientific supply catalogues offer mild acids that can simulate digestion, and then paper towels can be used to mimic the absorption power of the villi in the small intestine.
Don't Waste the Waste
You can't study the wastes left behind by the human excretory system, of course, but you can study animal wastes. Owl pellets, for instance, are available from scientific supply catalogues for dissection; studying the pellets tells observers a lot about owls, but it can also illustrate discussions about the nature of the excretory system and the kinds of waste that are excreted. If any of your students have been to a nature-themed camp, they may already know "The Scat Rap," a lighthearted and memorable song about how and why scientists study animal waste.
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