Human Digestion System – From the Food’s Perspective

, Human Digestion System – From the Food’s Perspective, The Travel Bug Bite

Hello, my name is Sally, and I am a chicken and vegetable salad. I am quite a nutritious salad, full of spinach, peppers, onions, sesame seeds and grilled chicken. Though I’ve enjoyed my time in the salad bowl, it’s time for what I was made for- to be eaten and digested by Isaac! 

Isaac likes to get a bit of everything in each bite. He puts as much variety as he can into his mouth, where the digestion process begins! His lips close around me and he begins to masticate, or chew. Saliva, produced by various salivary glands in his mouth, help to mix up all of my components. 

Isaac’s tongue also helps by kneading me throughout the mouth. The taste buds on Isaac’s tongue tell his brain how delicious I am as he chews and chews. 

The saliva in Isaac’s mouth not only keeps his mouth clean but also makes food slimy and easier to digest. Now, instead of separate pieces of a salad, I am now a greenish ball of chewed-up food called bolus. I’m eager to begin my journey down Isaac’s pharynx! I wave to the uvula, that hanging sack at the back of his mouth, as Isaac swallows. 

It’s a good thing Isaac has an epiglottis, or I’d be going down his wind pipe and into his lungs. When he breathes in, the epiglottis opens, and air goes into his lungs. If he’d been talking while eating me, I might have gone down the wrong pipe! Luckily, the epiglottis was in the right place and I’m passing into the pharynx. On my way down, I see the Eustachian tubes, which bring balance the air pressure in Isaac’s ears so he doesn’t get a headache. 

Now I’m entering the esophagus, where I no longer need to share the space with the air that Isaac breathes in. This digestion highway is reserved only for bolus like me. At the top of Isaac’s esophagus, there’s a sphincter that opens when Isaac is swallowing, allowing me to pass. I hear a loud pumping sound as I travel down the esophagus and realize I am right next to Isaac’s heart! 

At the lower end of Isaac’s esophagus, there’s another esophageal sphincter, and this one is almost always closed. It opens up to allow me through and immediately closes. If it didn’t do this, the fluids from Isaac’s stomach would travel into his esophagus when he went to bed, causing some pretty serious heartburn. 

It’s only taken about ten seconds to travel down this 25cm canal, and now I’m ready to enter Isaac’s stomach. This is where the real action begins! The body of Isaac’s stomach contains a mixture of gastric juices, mostly hydrochloric acid and water. I’m churned and churned in the stomach until I’m no longer bolus, but chyme – a somewhat liquid substance that is ready to travel down the funnel-like antrum of the stomach, past the duodenum, and into the small intestine. 

I’ve never really been sure why they call it the “small” intestine. After all, it’s 700 cm long – almost four times Isaac’s height! It fits snuggy inside Isaac’s gut by twisting and turning back and forth. I get a little dizzy as I pass through this 3cm-wide canal. As I go by, millions of little finger-like projections called villi absorb my nutrients through their blood vessels. If you flattened out all of the absorbing tissue in the small intestine, you would have a surface bigger than a tennis court! 

Now I’m starting to look more and more like what you see in the toilet when you go Number Two. I’m ready to pass into the large intestine, which is twice the width of the small intestine but only a quarter of the length.

As I travel back up, around and down, Isaac’s large intestine absorbs my water and salt and any last bits of me that his body finds useful. Having given Isaac all his body can use, I’m not bolus or chyme anymore, but just plain old feces. It’s no longer necessary for me to be in Isaac’s body, so peristaltic contractions continue to send me onward until I reach the rectum, which fills up and tells Isaac that it’s time for him to go.

Luckily, the act of defecation is usually voluntary, so Isaac can wait for a safe moment to let me go. I finally exit his body through his anus, happy to have served my purpose. 



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