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38
Chapter 3 – Digestion, Absorption, and Transport
Learning Objectives
After completing Chapter 3, the student will be able to:
3.1 Explain how foods move through the digestive system, describing the actions of the organs, muscles, and
digestive secretions along the way.
a. List the segments of the digestive tract in order from the mouth to the colon.
b. Explain the mechanical processes of digestion in order of occurrence in the digestive tract.
Assignments and Other Instructional Materials
The following ready-to-use assignments are available in this chapter of the instructor’s manual:
• Case Study 3: Managing GI Discomfort
• New! Worksheet 3-1: Chapter 3 Crossword Puzzle
1
• Worksheet 3-2: Digestion, Absorption, & Transport—DAT
2
• Worksheet 3-3: Food Habits, Digestion, and Absorption
3
• Worksheet 3-4: Further Exploration on Digestion (Internet Exercise)
• New! Critical thinking questions with answers
Other instructional materials in this chapter of the instructor’s manual include:
Lecture Presentation Outline
4
Key to instructor resource annotations (shown to the right of or below outline topics):
TRA = Transparency acetates: 13e = 13th edition, 12e = 12th edition, 11e = 11th edition, 10e = 10th edition
Website = Available for download from book companion website: HN = student handout
IM = Included in this instructor’s manual: CS = case study, WS = worksheet, CA = classroom activity
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I. Digestion
A. Digestion – Explain the processes of digestion and absorption and describe the challenges associated with
digestion, including:
1. Preventing interference between breathing and eating
2. Foods must pass through the diaphragm to enter the stomach
B. Anatomy of the Digestive Tract – Explain and describe the sections of the gastrointestinal (GI) tract
including (Figure 3-1): 12e TRA 3; IM CA 3-2
1. Mouth Website HN 3-4
a. Mastication
2. Esophagus
3. Stomach
4. Small Intestine
a. Gallbladder
5. Large Intestine (Colon) (Figure 3-2)
a. Ileocecal valve
b. Rectum
c. Anus
d. Appendix
C. The Muscular Action of Digestion – Explain how the muscular action of digestion is under autonomic
control; define and explain the following: 10e TRA 23, 24; IM HN 3-1
1. Peristalsis
D. The Secretions of Digestion – Describe the secretions involved in digestion, including:
12e TRA 4; 10e TRA 26
1. Digestive enzymes: catalysts in hydrolysis
2. Saliva from the salivary glands (Figure 3-5)
3. Gastric juice
4. Pancreatic Juice & Intestinal Enzymes – Pancreatic juice: enzymes and bicarbonate
5. Bile
a. Where is it produced
40
E. The Final Stage – Explain the final stages of digestion (Figure 3-7)
2. Vitamins, minerals, and water
4. Recycling of usable materials
II. Absorption – Describe and explain the process of absorption including: 10e TRA 27
A. The types of absorption (Figure 3-8)
1. Simple diffusion
B. Anatomy of the Absorptive System – Describe the anatomical structures involved in absorption
10e TRA 28
1. Villi (Figure 3-9)
2. Microvilli
3. Goblet cells
III. The Circulatory System Website HN 3-3
A. The Vascular System – Explain and describe the vascular system including: consists of arteries, capillaries,
and veins (Figure 3-10) 10e TRA 29, 30
1. Arteries
B. The Lymphatic System – Explain the lymphatic system including:
1. Lymph fluid
2. The thoracic duct
3. The subclavian vein
IV. The Health and Regulation of the GI Tract
A. Gastrointestinal Bacteria
1. Flora
2. Probiotics
3. Prebiotics
B. Gastrointestinal Hormones and Nerve Pathways 12e TRA 5; IM HN 3-2
1. Explain hormones including:
a. Gastin
41
V. Highlight: Common Digestive Problems IM CS 3, CA 3-4
A. Choking (Figure H3-1)
1. Food becomes lodged in the trachea
2. The larynx cannot make sounds
B. Vomiting
1. Body’s adaptive mechanism
2. Dehydration is a concern
3. May be self-induced as in eating disorders
C. Diarrhea
1. Characterized by frequent, loose, watery stools
2. Many causes, including certain foods or medications, IBS, colitis, & celiac disease
D. Constipation
1. Defecation habits are different among people
2. Many causes are possible
3. Hemorrhoids may be a problem
8. Strategies
a. High-fiber diet
b. Increased fluids
c. Exercise regularly
d. Respond quickly to the urge to defecate
E. Belching and Gas
1. Belching – Strategies
a. Eat slowly
F. Gastroesophageal Reflux (Figure H3-4)
1. Causes
a. Eating or drinking too much
b. Tight clothing
c. Changes in position
42
G. Ulcers
1. Peptic ulcers can be gastric or duodenal
2. Strategies
a. Take prescribed medicine
Case Study 3: Managing GI Discomfort
5
Mary Treat is a 68-year-old woman in reasonably good health. She is 64 inches tall and weighs 180 pounds. She
takes a daily multi-vitamin supplement and over-the-counter antacids for heartburn. Her usual diet includes lean
meat, chicken, fish, and fresh vegetables and seasonal fruit from her garden She now reports having severe
heartburn after a family reunion picnic over the Labor Day weekend and over the past two days has experienced
diarrhea and painful stomach cramps.
1. Based on her history, name at least two reasonable explanations for Mary’s sudden onset of diarrhea and
cramps.
2. What may explain Mary’s symptoms of heartburn?
3. If food poisoning is suspected, how might this be related to Mary’s regular use of antacids?
4. What immediate treatment would you suggest for her current symptoms?
5. What information and advice would you offer Mrs. Treat to help her avoid this type of gastrointestinal
discomfort in the future?
6. At what point would you advise her to seek medical care?
Answer Key
1. See Highlight 3. Answers may include food poisoning or other infections or a sudden change in diet.
Suggested Classroom Activities
The study of digestion and absorption requires learning an immense number of new terms. With beginning students,
it helps to introduce the digestive tract systematically, using a chart or DVD, and naming each part in sequence; then
to use all the names and continue using the chart while explaining the processes of digestion and absorption. Warn
students frankly that the task of learning the digestive system parts and their function is unglamorous but essential.
To bring the subject to life, digress at intervals to share related knowledge they find intrinsically interesting, about
choking, ulcers, and other topics.
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Classroom Activity 3-1: Obtaining Feedback From Students
Objective: Cultivating/maintaining a positive learning environment Class size: Any
Materials needed: 1 index card (3” x 5”) per student
Instructions: Obtaining feedback from students is an excellent way to monitor their progress and respond to their
needs. It only takes about 5 minutes of classroom time. Distribute 3 x 5 index cards—one per student. Instruct them
to write on one side of the card “What’s going well in class,” and on the other side, “What could be better.” The
feedback is usually valuable. Sometimes you can respond to distracting issues easily by adjusting classroom
temperature or outside noise levels. The process communicates that you care enough to ask for feedback.
Classroom Activity 3-3: “Who Wants to Be a Millionaire?” as a Tool for Review (and Fun)
6
Key concept: Review (at instructor’s discretion) Class size: Any
Purpose: To review material, motivate students to study, and have fun.
Materials needed: Computer projection system; Microsoft PowerPoint with animation and sound effects, plus review
questions on PowerPoint slides; overhead projector; chair and table; index cards; hat or jar
Setup: A computer projection system is used for the questions and an overhead projector for the point scale. The
room is set up with a chair facing a table, which faces the projection screen. The student selected to play sits in the
chair and has the three lifelines taped to the edge of the table. Once a student uses that lifeline, it is flipped over.
Student Reaction: Student comments have been very positive. It helps them review material and they have really
enjoyed the game and the effort put into its construction. There is a lot of encouragement from the class for the
student player. A few students in different semesters became “Millionaires” and the class cheered for them!
Comments: Although the initial construction was quite time consuming, once a set is done with the animation and
sound effects, the file can be copied and new questions substituted.
44
Classroom Activity 3-4: Evaluation of Products for Digestive Problems
Key concept: Digestive problems Class size: Any
Instructions: Have students bring over-the-counter products designed to treat common digestive problems
(heartburn, constipation, diarrhea, hemorrhoids). Discuss the appropriate and inappropriate uses of these
medications and adverse health implications associated with misuse and overuse of certain medications. For
example, overuse of medications for heartburn may foster a basic environment in the stomach and therefore hinder
iron absorption. Present alternative solutions to these common digestive problems as presented in Highlight 3.
Study Card 3 Answer Key
1. Since the mouth is the entry point for both foods and air, the epiglottis must cover the trachea as part of the
swallowing reflex so that swallowing and breathing don’t interfere with each other. The muscular diaphragm
Critical Thinking Questions
7
1. Identify and discuss potential factors related to the oral cavity that may impede the process of digestion of food.
What dietary changes would facilitate food intake for those with oral cavity problems?
2. Discuss how the pH environment of the various portions of the digestive tract facilitates the process of
enzymatic digestion.
3. Provide an example of how certain nutrients can enhance the absorption of others. How does this relate to
nutrient bioavailability? If the absorption of certain nutrients can be enhanced through the presence of other
nutrients or foods, how does this affect the concept of food combining?
4. What is the difference between probiotics and prebiotics in regard to gastrointestinal tract function? What
benefits does a synbiotic provide in the body?
45
5. Explain the concept of a negative feedback mechanism as it relates to gastric acid secretion.
6. How does the pancreas regulate digestive enzymes in order to promote intestinal health and well-being?
Answer Key
1. The digestive process begins in the mouth or oral cavity. If an individual has dental problems, this may affect
the ability to chew foods. Thus, the mechanical digestive process will be hampered, leading to the possibility of
the individual choking and/or potential aspiration. Individuals who have alterations in taste due to medication
2. The alimentary pathway utilizes a complex system of different biochemical secretions to facilitate the process
of digestion. The structural organs of the alimentary tract have their own acid-base environments that allow for
specific enzymes to act. For example, the stomach is highly acidic. Not only is this low pH the ideal
3. The ingestion of vitamin C (ascorbic acid) taken in conjunction with foods that are high in nonheme iron can
lead to increased iron absorption. Iron as a mineral is more readily available in heme food sources (animal
proteins). Vitamin C enhances the absorption of nonheme iron from both animal and plant food sources, thus
4. Probiotics are considered to be an important preventative health factor in maintaining healthy function of the
gastrointestinal tract. They are marketed by companies based on their ability to regulate normal bowel function
and prevent constipation and irregularity. Additionally, they are marketed as being effective against other health
conditions such as lactose intolerance and inflammatory bowel disease and as enhancing immune function.
46
5. A negative feedback mechanism involves a threshold response to an established baseline to increase secretion
of an identified substance with a desired effect. Once the desired effect has been reached, then the secretion of
6. The pancreas utilizes two methods to help regulate the actions of digestive enzymes. The first method is based
on dietary composition: the production of specific digestive enzymes is based on dietary intake. If a person eats
IM Worksheet Answer Key
Worksheet 3-1: Chapter 3 Crossword Puzzle
1. mouth
4. constipation
7. enzymes
10. celiac disease
Worksheet 3-2: Digestion, Absorption, & Transport—DAT
For digestion/enzyme activation and absorption columns, see Figure 3-7. Transport: proteins, small lipids, water-
Worksheet 3-3: Food Habits, Digestion, and Absorption
1. Promote: a, b, e, h; Impede: c, d, f, g, i
Worksheet 3-4: Further Exploration on Digestion (Internet Exercise)
47
Worksheet 3-1: Chapter 3 Crossword Puzzle
1
2
3
4
5
6
7
8
9
10
11
12
Across
Down
4. Eating high-fiber foods and drinking plenty of fluids
can help alleviate _____.
10. Involves an autoimmune response to gluten in foods
12. Contractions in GI tract muscles that move food
through the digestion process
1. Location where the process of digestion begins
2. Refers to the body’s overall plan to keep things
5. Muscles that control the flow of food throughout the
8. Microscopic hairs that cover the intestinal villi and
are used to absorb nutrients
9. How food is broken down into nutrients for
absorption
48
Worksheet 3-2: Digestion, Absorption, & Transport—DAT
For each of the nutrients listed below, indicate the mechanism of action for each of the processes identified above.
Nutrient
Digestion/Enzyme
Activation
Absorption
Transport
Hormonal
Regulation
Carbohydrates
Mouth → salivary
amylase
Stomach → no active
process
Small intestine →
pancreatic amylase
Large intestine → fiber
action
Primary site = small
intestine, via active
transport
Directly into the
bloodstream
Insulin, glucagon
Vitamins
Minerals
49
Worksheet 3-3: Food Habits, Digestion, and Absorption
Digestion transforms the foods we eat into nutrients and absorption moves nutrients from the GI tract into the blood.
Optimal digestion and absorption depend on the good health of the digestive tract, which is affected by such lifestyle
factors as sleep, physical activity, state of mind, and the meals you eat.
1. Identify which of these foods and food habits promote or impede healthy digestion and absorption.
Foods and Food Habits
Promote
Impede
a. Take small bites of food.
b. Chew thoroughly before swallowing.
c. Exercise immediately after eating to prevent weight gain.
2. Do you experience GI distress regularly?
3. What changes can you make in your eating habits to promote GI health?
50
Worksheet 3-4: Further Exploration on Digestion (Internet Exercise)
1. Arrange the organs that make up the digestive system in sequential order starting from the mouth.
a. anus
2. The liver and the stomach are considered to be "solid" digestive organs.
3. The lower esophageal sphincter closes the passage between the stomach and the pancreas.
4. Which of the following statements regarding factors affecting emptying of the stomach is/are true? Select all
that apply.
a. Carbohydrates spend the longest amount of time in the stomach.
b. The type of food eaten affects the stomach emptying rate.
c. The degree of muscle action of the small intestine affects stomach emptying.
d. Fats remain in the stomach for the longest time period.
5. Starches are digested in a two-step process, whereas sugars are digested in a one-step process.
6. Insoluble fiber takes on a gel-like texture in the intestines, making it easier to facilitate elimination.
7. Protein digestion begins in the stomach.
8. Bile acids combine with cholesterol and fatty acids to help fat molecules move into the cells of the mucosa.
a. True
b. False
9. Which of the following hormones regulate appetite?
10. Intrinsic nerves release acetylcholine and adrenaline.
a. True
b. False
51
Handout 3-1: Peristalsis and Segmentation
52
Handout 3-2: Examples of Hormonal Feedback Loops
