AP Biology…A Trip Through the Digestive System

Journey to the South – by an ISM AP Biology student.
On this episode of Magic School Bus, we will be going back in time to a glorious day right before the covid-19 event at a high school named ISM. We can observe a kind, brilliant Einstein look-a-like teacher passing out fresh baked cookies to his first class of the day. These cookies look delicious and students are delighted to get one each. Students do not hesitate a second and start feasting on the treats. By their high levels of the Ghrelin hormone, we can assume that they probably skipped breakfast coming to school on time or they just really love the teacher’s cookies.

Let’s shrink down our magic school bus and hide inside one of the cookies. The cookie was quickly eaten by a student. It is ingested through the mouth where the teeth and tongue initiate mechanical digestion. The enzyme amylase in the saliva is also capable of breaking down starch into simple sugars. We can observe the walls lining the oral cavity being made up of stratified squamous epithelium cells. The bus goes down with the chewed food through the esophagus, a tube that leads to the stomach. The wave-like muscle contraction moving the food is called peristalsis and it helps move the food around. Once we reach to the stomach, we fell down into the gastric juices of the stomach with digestive enzymes that help breakdown all the food. And of course, our bus did not corrode by the stomach acid, it’s a magic school bus. After a few minutes later, we find ourselves in a mixture of gastric juices and digested food called Chyme and as expected of a teenager’s diet, far too much sugar in one meal.

This Chyme mixture is further headed to small intestines. The gallbladder is notified of the high fat content and to release more bile to aid digestion of fat, turning them into fatty acids. The bile if produced by the liver and stored in the gallbladder. On the other hand, the pancreas is capable of producing enzymes to aid in digestion: trypsin and chymotrypsin for proteins, amylase for carbohydrates and lipase for fats. 

As we get to the small intestines, we see a whole canal walled with tentacle-like structures coated with smaller tentacle-like structure. These are called Microvilli which have very thin walls and a blood supply. The sugar, salts, fats, vitamins squeeze through the walls and go into the bloodstream. There are even lots of friendly bacteria which help digest the food and make vitamins for the body. They accompany us in this long journey. We had to go through a long time through the small intestines. More and more digested food contents get absorbed and fibers are the only ones to survive the digestion.

With a sharp turn, there lies a huge dark path where we almost fell into. It is the infamous appendix. We did not want to be trapped inside there. By being cautious, we made our way into the colon, the big intestine. Here, the walls squeeze and clasps the food contents absorbing out the water and making the waste material sturdy. Right in front of us lies, the anus where the waste is excreted out of the body. Before we end up in a shady place of ISM, we were able to teleport back into the world, magically. So that is the end for the trip through the digestive system.