Once you've chewed your food completely, go ahead and swallow. We'll follow it down the long squishy tunnel that connects your mouth to your digestive system. It's a little intimidating though, hovering at the top of a dark passage. We'll dangle from your uvula, that ball that hangs in the back of your throat for a moment. Above us is a light where you can see your tongue and teeth. What mysteries lie below? If we're going to discover every aspect of the digestive process, we need to venture forth! GULP!
Fun Fact! Scientists don't know what your uvula does! It might provide saliva for speaking. It might be there to make you gag if something gets caught. Or it might be a mini punching bag for your food to hit on its way down.
Ahead are ten inches of pink piping that lead us downwards through your ribcage. The walls are alive, pulsing and stretching. As we glide down, you'll hear the rise and fall of your lungs taking in oxygen, and there, to the left, you'll hear your heart pumping blood. Your esophagus is an organ that transports chewed up food from your mouth to your stomach. You can think of it as a tunnel through a large mountain, the quickest route for cars (or in this case, food) to travel from one location to another. While in this tunnel, try not to breathe and eat at the same time, or else there might be a horrible traffic accident.
There are two different kinds of traffic that travel down your esophagus, chewed up food and oxygen. Try to avoid cigarette smoke. If you do inhale smoke, your esophagus and lungs could wither like dying flowers. If you accidentally breathe while swallowing, your food or drink might end up down the wrong pipe! Not only is this painful, it's also embarrassing. Your windpipe is at the back of your throat and it leads the oxygen you breathe into your lungs. There's a wall between these two pipes, but just like a car on the freeway that doesn't mean food isn't able to go the wrong way.
Have you ever drunk a glass of water just a little too quickly? Suddenly, your drink comes spraying out of you with as much velocity as lava from a volcano! As you now know, your windpipe runs alongside your esophagus and your mouth functions as the entryway to both. How does your body figure out where to send air and where to send water? Do you actually consciously think about this when you drink? Of course you don't! Something in there is doing the work for you.
The epiglottis is a flap of skin that covers the entrance to your windpipe. It's the temperamental little guard of your lungs. If you thought your taste buds were picky ("Blech! Spit that out!"), they've got nothing on this thing. Your epiglottis is like a little traffic cop that says "Halt!" to water while waving oxygen through. It's so picky that if any sort of liquid touches it, it will flap open and release a burst of air that fires even a single drop back up the esophagus! While you're choking, you may not feel so grateful to the epiglottis, but it's a good thing to have for your lungs. I don't need to tell you that even a little fluid in there is not only painful, but terrible for breathing. So thank your epiglottis for being so stubborn. Just make sure no one's sitting in front of you when you're drinking.
Of course there can be problems with sharing the entrance to your lungs and stomach with the same pipe. People often overeat, sometimes causing a traffic jam in their esophagus. If a piece of food gets caught in a person's windpipe, they could be in some serious trouble. About fifty years ago, thousands of people were choking to death every year. More people were dying because of bad swallowing than from guns! Then a man named Heimlich decided to develop a technique that would turn him into a hero. The technique involved approaching a choking victim from behind, making a fist below their ribcage, and using the other hand to pull abruptly into their stomach. The movement will force the air out of the victim's lungs, hopefully rocketing the stuck piece of food out of their throat.
Being a good scientist, Mr. Heimlich knew he needed to understand the human body if he wanted to find a solution. Bear with me through this next part. Science can get a little creepy sometimes. He made a dog fall asleep by giving it an injection. Then he tied a piece of food to a string and pushed it down the dog's esophagus, forcing it to choke. He then tried many different ways to get the food out. The string was there to pull the food out just in case the new approach didn't work. He soon discovered the Heimlich maneuver, the most effective way to get food out of the esophagus fast. Thanks to Mr. Heimlich, great science, and a few unfortunate pooches, choking deaths plummeted!
Have you ever watched a snake digest? They don't just chew up their food and then swallow like mammals do. Instead, they wrap their mouths around a dead rat and then slowly work it back with their throat and body. Once your food leaves your mouth, your esophagus does something similar. Peristalsis is the pushing and squeezing motion that moves food down to the stomach and the rest of the digestive system. That's why it isn't difficult to drink or eat while lying down. Swallowing doesn't have anything to do with gravity. The good news is that you don't have to think about peristalsis. Your body will just push the food where it needs to go. You do, however, have to think about how some of your intestines resemble a snake . . .
Just the right size.
Brian Gratwicke Brian Gratwicke, CC BY 2.0 , via Wikimedia Commons
Imagine swallowing like a snake. To start, you'd use sensors in your flicking tongue to sense where the body heat of your prey is emanating from. Shh, you sense a rat in the brush. If you're a poisonous snake, you would bite it with your hollow teeth, injecting it with poison and paralyzing it so it won't struggle while you swallow. If you were a python, you could also constrict, or strangle, it to death with your rope-like body. I'll leave the hunting process up to you. Obviously, snakes get their food much differently than you; there's no driving through a drive-thru or buying meat in a package at the grocery store for snakes. This is not where the differences end, though. Hunting your prey is only the beginning of a snake's digestion story.
Now it's time to consume the rat! I apologize in advance. Let's hope this is the last time you have to eat a rat. As a human, your jaw can open to about 35 degrees. If you were a snake, though, you could open your jaws to an amazing 150 degrees! You could swallow food whole even if it's bigger than your head! Your jaw would stretch and stretch, practically coming apart until you fit it over your prey's head. Next, you don't gulp so much as "walk" your jaw around the animal, your teeth taking one little step forward at a time. Once the rat reaches your esophagus (which stretches down most of your long, skinny body), you'll have to push it back while simultaneously crushing it with your muscles. Imagine breaking bones inside your throat! From now on, the human digestion process may not seem so disgusting.
Have you ever tried sliding down a slide with bare legs? Your skin drags along the metal, slowing your velocity. Now try sliding down a water slide with bare legs. Even if your skin is touching the slide, you'll rocket down as fast as gravity can pull you back down to the planet. Like water in a water slide, your body generates liquid to make your food slide through your digestive system more quickly. Mucus is the slimy liquid that helps your food move through your esophagus to your stomach without getting stuck. You know mucus -- when it comes out of your body you call it snot or boogers. The only real difference between your esophagus and a water slide is that your food does not cry "Wheeeeee!" while it slides down.
Watch out, food coming through!
kallerna, CC BY-SA 3.0 , via Wikimedia Commons
Look up toward your uvula. You can't even see the light from the mouth anymore. We've only traveled ten inches, pushed down your esophagus by peristalsis like food through a snake, and we're still in one piece. A large cave lies ahead; it doesn't smell wonderful, but we must go. We are scientists, after all.
References:
"Science for Kids: The Digestive System." Ducksters. Technological Solutions, Inc. (TSI), June 2014. <http://www.ducksters.com/science/digestive_system.php>
Academic Kids. "Peristalsis." Academic Kids, 2010. <http://www.academickids.com/encyclopedia/index.php/Peristalsis>
Kid's Health. "Digestive System." Kids' Health, 2013. <http://kidshealth.org/PageManager.jsp?dn=KidsHealth&lic=1&ps=107&article_set=20538&cat_id=20090>
Radiolab. "The Man Behind the Maneuver." Radiolab, 2013. <http://www.radiolab.org/blogs/radiolab-blog/2013/mar/05/heimlich/>
Kids Health. "Word! Epiglottis." Kids Health, 2012. <http://kidshealth.org/kid/word/e/word_epiglottis.html>
Perry, Lacy. "How Snakes Work." August 2004. HowStuffWorks.com. <http://science.howstuffworks.com/zoology/reptiles-amphibians/snake4.htm>