Anatomy And Physiology

A Trip down the Digestive System



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One day I was sitting next to Anthony at lunch. Suddenly, I was mysteriously shrunk to microscopic size! Now I am on a slice of pepperoni pizza and am about to be eaten! As soon as Anthony smells, sees, or even thinks of food his salivary glands start functioning as they are now. Luckily, I am in a special, clear capsule that allows me to not be digested. At the same time, I can see all the magnificent parts of the body. I happened to have a few helpful gadgets with me: a random digestive fact generator, a guide book to the digestive system, and some food just to keep my body satisfied.

All around me I see a wet, slimy liquid coming from the saliva glands. This liquid is called saliva or spit. The salivary glands produce 1.5 liters of saliva each day. The pizza seems like it is being moistened. According to my guide book, the saliva is made up water, dissolved mucus proteins, and amylase. The teeth, which look like large white “blades”, are now chewing and grinding up the food. It looks like my random digestive fact generator has something to say. “Go ahead.” “With every bite the molars apply 200 pounds of force behind each bite!” “Wow! I’m glad I’m in this special capsule. Or else I would be dead meat!”

A few seconds have passed and the mouth has created a moist, slippery ball called a bolus. It seems like the tongue has pushed the bolus to the back of the mouth triggering the swallowing reflex. The pizza crust is already beginning to be digested due to the amylase. As I look down, I see something closing over the windpipe. That must be the epiglottis. Every time the swallowing reflex occurs in covers the windpipe so no food goes to the lungs.

As I go down the esophagus I can feel the muscular contractions and relaxations pushing the bolus along with me down to the stomach. This process is called peristalsis. PLOP! Now I’m in the stomach. The esophageal sphincter closed as soon as the bolus fell into the stomach. This prevents anything from going back up into the esophagus. Eww! What are all these liquids sloshing around? Oh! I found it! The liquids in the stomach are a mixture of hydrochloric acid and pepsin. This mixture is highly acidic so that it can digest the food. Due to its high acidity, the stomach needs to be coated with mucus. The mucus prevents the gastric acid from penetrating the stomach. If there is a spot that is not coated, an ulcer may occur. The churning of the stomach must help the digestive juices do their job even better. The churning action is caused by three layers of muscles. The combined actions of the gastric juice and the churning of the stomach make sure almost no solid material is left. The liquid version of the food is referred to as chime.

All the food and liquid Anthony is drinking is coming down the esophagus and landing in the stomach. As more of his lunch makes it way down here, the stomach gradually expands. When empty, the stomach can hold 50ml, but when it needs to, it can expand to be able to hold 1 liter. If the stomach needs to get rid of something that was ingested, it can open up the esophageal sphincter and sends the food back up the esophagus and out the mouth. This process is known as vomiting.” Cool! It’s another random fact time!” “Foods from different food groups are broken down and different rates. For example, the pizza crust, a carbohydrate, is digested comparatively quickly. On the other hand, the sausage is still remaining since it is made up of fat and protein. Only carbohydrates undergo chemical digestion in the mouth.” “Wow! Those are some interesting facts!”

Ugh, I’m getting tired now! I’ve been here for 4 hours! I’m going to take a nap. See you it a bit.

As I’m asleep I don’t realize I am moving downwards towards a round black hole. It’s the pyloric sphincter. It controls the amount of food that goes down the small intestine. WSHHH… Ahh! What’s happening? Then I realized I was going down the duodenum. It is 25 centimeters long and is the first section of the small intestine, which itself is 7 meters long!

I see more liquids coming out from all around me. This time it is pancreatic juice. Pancreatic juice is packed with enzymes that help digest carbohydrates, proteins, and fats. The pancreas produces about 1.5 liters of this juice each day. Pancreatic juice is not acidic. In fact, it neutralizes the acid from the stomach. Now, another liquid is added to the mixture, bile. According my guide, the bile is produced in the liver and stored in the gall bladder. Wow, I can see all the parts of the pizza being broken up! The sausage that was partially digested in the stomach is now being acted upon by the intestinal and pancreatic juices. The crust and all the other bread are now in their final steps to becoming simple sugars. The bile breaks down the large fat droplets into smaller ones so that they can move easily with the juices from the small intestine and the pancreas.

Now I’m at the point when I can say, “the digestion is complete”. The particles are now simple enough to be absorbed through the lining of the small intestine. The small intestine is lined with villi and microvilli which absorb all the nutrients from the chyme. I’m now at the end of the small intestine. I see two openings. I check the map in my guide to see where each one goes. The one to the right is the entrance to the appendix. Nowadays, the appendix is useless and is actually a risk since it can get blocked and then infected. Though, scientists believe that the appendix once helped humans digest the cellulose in plant matter. To the left is the entrance to the large intestine. That’s where I’ll be going so Anthony doesn’t end up in the hospital.

The large intestine is also called the colon. The name of the material that passes through the colon is called feces. The job of the colon is to absorb all the liquid from the feces. If the feces go through the colon too fast, diarrhea may occur. If the feces go through the colon too slow, constipation may occur. Eww! It smells awful in here! It’s the smell of the bacteria in the large intestine feeding on undigested food. Anthony could let the gas pass out through the anus but that wouldn’t be very polite.

Now I’m combined with all the feces at the end of the small intestine in the rectum. Suddenly, the colon contacts powerfully and all the feces are “shot” out in to the white bowl. Luckily, I am able to hold on to the rim of the bowl and make it out safely. When Anthony walks out of the restroom I greet him as if nothing happened.

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