Zaqui and his father Alberto embark on a secret mission inside a spaceship to learn about the digestive system. They travel through the mouth, esophagus, stomach, small intestine, large intestine and are eventually expelled in the anus and toilet. Along the way, they observe food being broken down by teeth, saliva, gastric juices, pancreatic juices and bile into smaller particles that can be absorbed for energy or eliminated as waste. After two days traveling through the entire digestive system, they return to their agency to report on their findings.

1. Hello! My name is Zaqui and I am going to travel through the
digestive system with my father Alberto. We are on a secret
mission to know everything about it. We are in a space ship inside
a sandwich. Do you want to join us?

2. Our trip started. We felt how the boy that was going to eat us lifted the sandwich we
occupied and opened his mouth. When we were inside it, he closed the mouth and
started biting it with his teeth (the canines, the molars, the premolars and the
incisors). We saw bits of sandwich being cut by the incisors, torn by the canines,
crushed by the premolars and grinded by the molars. Luckily, we didn´t suffer such
bad luck because my father was a very good pilot and escaped from every single
tooth. After that we were covered in saliva. Even though the 95% of it was water, the
other 5% (enzymes) were making the bits of sandwich break into pieces. The saliva
would have needed more time to brake up the food if it hadn´t been for the teeth. Our
ship didn´t break up because it was protected against enzymes. We saw the tongue
licking us and the food (the boy was tasting it). Then, it pushed us to the pharynx.

3. We advanced through the pharynx but ended up in front of two other tunnels. One
lead to the respiratory system and another lead to the digestive system. A kind of
`door´ called epiglottis closed the tunnel that lead to the respiratory system, so we
advanced through the other tunnel with the food. We where now in the oesophagus.
We also noticed the food had turned into a cud because of al the teeth and saliva.
Furthermore, it wasn´t falling but was being pushed. We turned the motors off so we
didn´t waste energy (after all, we were being pushed by the oesophagus).The ship and
the cud were being carried to the stomach.

4. After a 25 cm travel through the oesophagus, we fell to the stomach. We floated in a
pool of gastric juices which were breaking the food into smaller pieces. We had been
warned the process took from one to three hours, so we had enough time to observe
a curious fact: the proteins inside the meat the sandwich had were resisting the acid,
so the stomach was pouring a different kind of gastric juice called pepsin that was
stronger and would brake the proteins. We also noticed we were being pushed in all
directions so the food was well mixed with the acids.

5. After some time, we were allowed to go to the small intestine. It wasn´t actually that
small… it measured nearly eight meters! But it was crumpled and squashed so it didn´t
occupy that much space. After a while, we where face to face with the ampoule toilet.
We found out more acids came from it. They were the pancreatic juices (coming from
the pancreas) and the bile (coming from the liver). The pancreatic juices broke the fats
and the bile finished with the proteins. We stopped so the enzymes inside the acids
broke up the food. If the food had been broken enough, it would have an atomic size
and would be soluble. Then, they could pass through the small capillaries that led to
the blood and be used as energy. But, some pieces and useless parts of the cud were
left behind and had to get out of the boy. We continued with them.

6. We went from the small intestine to the large intestine (which was smaller than the
small intestine). There, all the water on the bits of sandwich were taken and the bits
taken to the final part. It was the anus, which was a hole through which the remaining
bits and the ship were going to be expelled as dregs. We waited until the boy decided
to go to the toilet and were expelled.

7. We ended up in a toilet with the dregs. It had been a very good trip but we realized
how much time we had spent inside the body: 48 hours! It was time to go back to the
agency and inform our superiors. Thank you for joining us!