A simple matter of digestion 2009.05.13
By DAVID GREEN
It’s starts at the mouth and it ends...well, somewhere else down the line.
Jim Bauer’s eighth grade science class at Morenci Middle School was about to act out the story of digestion Wednesday morning when they hit a couple of last-minute glitches.
The large intestine was absent; the anus had been suspended. A few students were calling for a delay—more time to study—but Mr. Bauer would have none of that.
He noted that the media was present and, with a couple of adjustments, the show would go on.
A new anus was assigned, the small intestine support group was shifted and the players took their parts behind a table at the front of the room. The table was empty but for a large bowl of popcorn.
Mr. Bauer had a question for the liver and pancreas, who stood off to the side.
“Why aren’t you with the others?”
The liver comes through with the correct answer: They aren’t actually part of the digestive system, but they produce substances to help with digestion.
The Mouth kicks off the trip through the alimentary canal, explaining that the enzyme amylase found in saliva starts to break down starches in food.
She pours a container of spit into the bowl—actually it was water representing saliva—and mixes it around.
Good start, Mr. Bauer says, but does food really look like that after it’s been chewed?
The Mouth goes to work on the popcorn, crushing it with her fingers to create a soppy mixture.
Next comes the Esophagus, the muscular tube connecting the mouth and the stomach. It’s lined with mucus to help the food slide down more easily. There’s also the epiglottis to close off the windpipe (trachea) to prevent food from sliding down that tube. Muscular contractions (peristalsis) move the food along its way.
“Is it possible to eat upside down?” Mr. Bauer asks.
The answer is “yes.”
The Esophagus is pleased that she isn’t required to touch the chewed popcorn. She merely passes the bowl on to the Stomach.
This is where most mechanical changes take place with the food. The Stomach adds a beaker of pepsin to the mix, along with hydrochloric acid to help the pepsin work and to kill off the bacteria. Proteins are turning to amino acids, and spectators are looking at the unappetizing mess that was recently popcorn.
The Stomach sloshes the mixture around and hands the bowl off to the Small Intestine, an organ measuring about six meters in length. If all the villi—tiny finger-like projections—were spread out, they would cover an area about the size of a tennis court.
In comes bile from the liver, and trypsin, lipase and amylase from the pancreas. The intestine creates its own peptidase and multase to further break down proteins and sugars.
A little more mixing and off the disgusting mishmash goes to the Large Intestine (about one and a half meters long). Nutrients and proteins have been absorbed into the bloodstream by this time. The Intestine uses his hands to compact the substance and squeeze out the liquid.
There’s nothing left but passage through the Anus.
“Could you give us your best anus imitation?” Mr. Bauer asks Cody Powell.
He does and the show is over. The amazing trip through the digestive system has ended. Students will soon be off to the cafeteria to apply their classroom knowledge to a real-life situation.
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