Simple Sugars:
A Simple Story
Why does your body need to break down starch into sugar? The reason is that the body cannot use
carbohydrates until they are in a form that is simple enough to dissolve in water and pass through cell
membranes into the blood and, ultimately, to the body's cells.
Starches are made up of chains of simple sugar particles that are held together by chemical bonds. But once the
starch is chewed and acted on by digestive enzymes in the mouth and small intestine, the bonds that hold the
links of the starch chain together break apart. The result is simple sugar particles. These particles are small
enough to move through the body and enter the cells. They provide cells with nutrients they need to do their
jobs.
Read about it here in Simple Sugars: A Simple Story. Then answer the questions.
INTO THE SYSTEM
Peppi and Bollo are ready for their first investigation. It's noon.
Time for lunch.
They hop aboard a slice of pizza (topped with mushrooms,
sausage, and green pepper) and enter a human mouth.
"Who's our host?" says Bollo.
"Her name is Joanne. She's 18— an adult as far as human
digestive systems are concerned. She's healthy, too. No digestive
problems. If we can discover what's going on in Joanne's digestive
tract, we'll have a good idea about human digestive activity," replies
Peppi.
Watch out, Joanne! You are about to be
invaded by aliens
"Wow, its dark," says Bollo. "And wet and slippery, too. Watch out for those huge white blades!"
"The liquid is spit," says Peppi. "Its formal name is 'saliva.' Saliva is produced by three pairs of glands in the
sides and the back of the human mouth. The salivary glands go to work whenever a human smells, sees, or
even thinks about food. Once food is in the mouth, the saliva moistens it and makes it easier to handle. The
salivary glands produce about 1.5 liters of saliva each day. "And those 'blades,'" Peppi goes on, "are teeth. Adult
humans usually have 32 of them."
Peppi and Bollo take a look around. It's a busy scene. The front teeth, or incisors, go to work first. These sharp
teeth act like scissors. The canine teeth, at the sides of
the mouth, are pointy. They cut up the food some more. The tongue is muscular. It helps move food around. It
moves the pizza to the back of the mouth, where the heavy-duty work of chewing goes on. The broad, flat
bicuspids and molars grind the food and make it soft. Meanwhile, the saliva is doing its thing. It moistens the
food and makes it easier to chew.
"This tearing, grinding, and mixing," Peppi says, "is called mechanical digestion.
And although we can't see it, it's important to know that saliva contains an enzyme
called amylase. The enzyme activity marks the beginning of chemical digestion."
"Hold on a minute. You're going too fast," says Bollo. "What's an enzyme?"
"An enzyme is a special protein produced by the body. Digestive enzymes help
the body break down nutrients into forms that the body can use. Amylase, for
example, helps break down the starch in pizza to simple sugar. As we continue, we'll
see other enzymes that help digest other types of nutrients."
"The human mouth is efficient," notes Bollo. "It's only been a few seconds, and I
can't even recognize that bite of pizza. It looks like a big, soggy ball."
"You're right. That ball of food is called a bolus," says Peppi. "And if I took out my testing equipment, I could
show you that the pizza crust is already starting to be digested—because of the action of amylase."
Down the Tubes
"Eeeeeeee!" shrieks Bollo. Before he can say more, he and Peppi are pushed up against the roof of the mouth.
It's a tight squeeze. Then they start moving backward. The bolus has triggered a swallowing reflex. Goodbye,
mouth!
Looking down, they see something close over one of the two tubes below them.
"The epiglottis," says Peppi. "Each time a human swallows, it closes over the wind-
pipe to make sure that food goes to the stomach. The windpipe leads to the lungs, and you don't want any food
in there!"
"One tube for air, one for food. The human body is specialized," says Bollo.
"You're right," says Peppi. "You're also going to find out that these specialized
organs and systems need each other. They work together to help keep the body in balance. Now keep your
eyes open. We're traveling through the second organ of the digestive system, the esophagus."
Down and down they go, squeezed by muscular contractions of the walls of this dark- pink tube. Then all of a
sudden, another tight squeeze, and pop! The spies arrive in the stomach. They have passed through the last
gatepost on the road to the stomach, the lower esophageal sphincter. The sphincter is a ring of muscle that helps
keep food that has been swallowed where it should be—in the stomach.
"What happens now?" asks Bollo.
"I like your curiosity, Bollo. Stay posted. Our journey will soon continue," Peppi replies.
Answer these questions completely:
1. Why does your body need to break down food?
2. What do Peppi and Bollo do to learn about the digestive system?
3. What simple machine do ‘those huge white blades’ make you think of? Why?
4. What process does the enzyme amylase in saliva begin?
5. What is the purpose of the epiglottis?
6. What is the name of the tube that leads Peppi and Bollo to the stomach? How does it
work?
7. What do you predict will happen in the next part of Peppi and Bollo’s journey?
1. What happens to Peppi and Bollo in the stomach?
2. What is the relationship between pepsin and hydrochloric acid?
3. How do the muscles in the stomach work?
4. Why is there mucus in the stomach?
5. What are some things that can go wrong with the stomach? Explain.
6. Why did the pizza crust digest faster than the sausage?
7. How do you think the author might have come up with the character names Peppi and Bollo?
1. What is the duodenum?
2. Why do people call the small intestines “small”? Are they small? Explain.
3. How are the pancreas, the liver and the small intestine related?
4. How is pancreatic juice different from the juices in the stomach? Why is it different?
5. What do carbohydrates, proteins and fats break into?
6. When are the particles of food small enough to be absorbed through the lining of the small intestine?
1. What name does Peppi use for the large intestine? What are some other terms that can be used to name the large
intestine or parts of it?
2. What is the appendix and what can go wrong with it?
3. How does the large intestine contribute to maintaining homeostasis?
4. What is feces and what happens if it moves too quickly or too slowly through the large intestine?
5. What produces gas in the large intestine?
6. Summarize what Peppi and Bollo learned about the Digestive System during their adventure.
7. If Peppi and Bollo were to go on another adventure, what body process would you like them to explore next?