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# 23.3: The Digestive System

Difficulty Level: At Grade Created by: CK-12

## Lesson 23.3: True or False

Name___________________ Class______________ Date________

Write true if the statement is true or false if the statement is false.

_____ 1. To get glucose from food, digestion must occur.

_____ 2. Chemical digestion is the physical breakdown of chunks of food into smaller pieces.

_____ 3. The GI tract is one long tube that connects your mouth to your anus.

_____ 4. The small intestine is part of the GI tract and is about 23 feet long in adults.

_____ 5. Mechanical digestion occurs mainly in the small intestine.

_____ 6. Shellfish and chicken cause common food allergies.

_____ 7. Your mouth is an organ of the digestive system.

_____ 8. Absorption is the process in which nutrients pass into the bloodstream, where they can circulate throughout the body.

_____ 9. Nutrients the body needs in relatively small amounts are called macronutrients.

_____ 10. The major salivary enzyme is maltase, which aids in the digestion of carbohydrates.

_____ 11. Minerals are chemical elements that are essential for life.

_____ 12. Most nutrients are absorbed into the blood in the jejunum.

_____ 13. Most chemical digestion takes place in the stomach.

_____ 14. According to MyPyramid, ice cream and chips can be eaten every day.

_____ 15. Most people can survive only a few days without carbohydrates.

Name___________________ Class______________ Date________

Read these passages from the text and answer the questions that follow.

Digestion and Absorption: The Small Intestine

The small intestine is a narrow tube about 7 meters (23 feet) long in adults. It is the site of most chemical digestion and virtually all absorption. The small intestine consists of three parts: the duodenum, jejunum, and ileum.

Digestion in the Small Intestine

The duodenum is the first and shortest part of the small intestine. Most chemical digestion takes place here, and many digestive enzymes are active in the duodenum (see Table below). Some are produced by the duodenum itself. Others are produced by the pancreas and secreted into the duodenum.

Enzyme What It Digests Where It Is Made
Amylase carbohydrates pancreas
Trypsin proteins pancreas
Lipase lipids pancreas
Maltase carbohydrates duodenum
Peptidase proteins duodenum
Lipase lipids duodenum

The liver is an organ of both digestion and excretion. It produces a fluid called bile, which is secreted into the duodenum. Some bile also goes to the gall bladder, a sac-like organ that stores and concentrates bile and then secretes it into the small intestine. In the duodenum, bile breaks up large globules of lipids into smaller globules that are easier for enzymes to break down. Bile also reduces the acidity of food entering from the highly acidic stomach. This is important because digestive enzymes that work in the duodenum need a neutral environment. The pancreas contributes to the neutral environment by secreting bicarbonate, a basic substance that neutralizes acid.

Absorption in the Small Intestine

The jejunum is the second part of the small intestine, where most nutrients are absorbed into the blood. The mucous membrane lining the jejunum is covered with millions of microscopic, fingerlike projections called villi (singular, villus). Villi contain many capillaries, and nutrients pass from the villi into the bloodstream through the capillaries. Because there are so many villi, they greatly increase the surface area for absorption. In fact, they make the inner surface of the small intestine as large as a tennis court!

The ileum is the third part of the small intestine. A few remaining nutrients are absorbed here. Like the jejunum, the inner surface of the ileum is covered with villi that increase the surface area for absorption.

Questions

1. What happens in the small intestine?

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2. List and describe three enzymes of the small intestine.

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3. What is bile? What is the function of bile?

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4. What are the three parts of the small intestine?

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5. What is the role of the villi in the jejunum?

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## Lesson 23.3: Multiple Choice

Name___________________ Class______________ Date________

Circle the letter of the correct choice.

1. The gastrointestinal tract is a long tube that includes
1. the mouth, stomach, intestines and anus.
2. the mouth, stomach, intestines, liver and anus.
3. the mouth, stomach, intestines, liver, gallbladder and anus.
4. the mouth, stomach, intestines, liver, gallbladder, pancreas and anus.
2. The organs of the GI tract are lined with
1. enzymes that break down food.
2. cilia to sweep food through the GI tract.
3. mucous membranes that secrete digestive enzymes and absorb nutrients.
4. all of the above.
3. Which of the following statements is the best description of digestion?
1. Mechanical digestion is the physical breakdown of food, and chemical digestion is the chemical breakdown of food molecules.
2. Chemical digestion is the physical breakdown of food, and mechanical digestion is the chemical breakdown of food molecules.
3. Chemical digestion is the physical breakdown of food, and mechanical digestion is the mechanical breakdown of food molecules.
4. Mechanical digestion occurs in your mouth, and chemical digestion occurs in your stomach.
1. pepsin begins the acidic digestion of proteins.
2. amylase begins the chemical digestion of carbohydrates.
3. amylase begins the mechanical digestion of carbohydrates.
4. amylase, pepsin, trypsin, and other enzymes start to break down food.
5. The stomach
1. digests food both mechanically and chemically.
2. contains pepsin, which chemically digests protein.
3. has an acidic environment, which kills bacteria in food and is needed for the stomach enzymes to function.
4. all of the above
6. In the small intestine,
1. most nutrients from food are absorbed into the blood.
2. excess water is absorbed from food.
3. the mechanical breakdown of food is completed.
4. partly digested food is stored until ready for the final aspects of digestion.
7. The large intestine includes
1. the duodenum, jejunum, and ileum.
2. the GI tract, from the mouth to the anus.
3. the cecum, colon, and rectum.
4. the duodenum, jejunum, ileum, cecum, colon, and rectum.
8. Nutrients
1. include carbohydrates, proteins, lipids, and water.
2. are needed for energy, building materials, and control of body processes.
3. include chemical elements like calcium and potassium.
4. all of the above

## Lesson 23.3: Vocabulary I

Name___________________ Class______________ Date________

Match the vocabulary word with the proper definition.

Definitions

_____ 1. an involuntary muscle contraction that moves rapidly along an organ

_____ 2. a relatively wide tube that connects the small intestine with the anus

_____ 3. a long tube that connects the mouth with the anus

_____ 4. the process in which substances pass into the bloodstream

_____ 5. shows the relative amounts of foods in different food groups you should eat each day

_____ 6. substances the body needs for energy, building materials, and the control of body processes

_____ 7. a long, narrow tube that passes food from the pharynx to the stomach

_____ 8. the breakdown of food

_____ 9. consists of organs that break down food and absorb nutrients

_____ 10. the chemical breakdown of large, complex food molecules

_____ 11. microscopic, finger-like projections of the jejunum

_____ 12. a sac-like organ in which food is further digested

_____ 13. organic compounds that are needed by the body to function properly

_____ 14. the site of most chemical digestion and virtually all absorption

_____ 15. the physical breakdown of chunks of food

Terms

a. absorption

b. chemical digestion

c. digestion

d. digestive system

e. esophagus

f. gastrointestinal tract

g. large intestine

h. mechanical digestion

i. MyPyramid

j. nutrients

k. peristalsis

l. small intestine

m. stomach

n. villi

o. vitamins

## Lesson 23.3: Vocabulary II

Name___________________ Class______________ Date________

Fill in the blank with the appropriate term.

1. Peristalsis is an ____________ muscle contraction that moves rapidly along an organ.

2. The ____________ is a sac-like organ in which food is further digested both mechanically and chemically.

3. The small intestine consists of three parts: the duodenum, ____________, and ileum.

4. Macronutrients include carbohydrates, ____________, lipids, and water.

5. ____________ shows the relative amounts of foods you should eat each day.

6. ____________ is the process in which substances pass into the bloodstream.

7. The large intestine consists of three parts: the cecum, ____________, and rectum.

8. ____________ is the process in which wastes leave the body.

9. ____________ digestion is the chemical breakdown of large, complex food molecules into smaller, simpler nutrient molecules.

10. Mechanical ____________ is the physical breakdown of chunks of food into smaller pieces.

11. The ____________ is where most nutrients are absorbed into the blood.

12. Body mass ____________ is an estimate of the fat content of the body.

## Lesson 23.3: Critical Writing

Name___________________ Class______________ Date________

Thoroughly answer the question below. Use appropriate academic vocabulary and clear and complete sentences.

Identify three classes of nutrients and their functions in the human body.

Feb 23, 2012

Oct 07, 2015