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Chapter 3 – Digestion, Absorption, and Transport
Learning Objectives
After completing Chapter 3, the student will be able to:
1. List the segments of the digestive tract in order from the mouth to the colon.
2. Explain the mechanical processes of digestion in order of occurrence in the digestive tract.
3. List the five organs and their secretions which assist in the breakdown of food.
Assignments and Other Instructional Materials
The following ready-to–use assignments are available in this chapter of the instructor’s manual:
• New! Case study
• Worksheet 3-1: Chapter 3 Crossword Puzzle
1
Other instructional materials in this chapter of the instructor’s manual include:
• Classroom activities
• Worksheet answer keys (as appropriate)
• New! Handout 3-1: Examples of Hormonal Feedback Loops
Lecture Presentation Outline
4
“Of special interest to…” symbol key: = Hot Topic = Personal Health
= Health Care Professionals = Science Majors
Key to instructor resource annotations (shown to the right of or below outline topics):
PL = Available on Power Lecture DVD-ROM (ISBN 0538797592)
TRA = Transparency acetates: 12e TRA = 12th edition, 11e TRA = 11th edition, 10e TRA = 10th edition
Website = Available for download from book companion website: HN = student handout
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I. Digestion
A. Digestion is the process of breaking down foods into nutrients to prepare for absorption while overcoming
the following seven challenges:
1. Preventing interference between breathing and eating.
2. Foods must pass through the diaphragm to enter the stomach.
B. Anatomy of the Digestive Tract – The gastrointestinal (GI) tract is the flexible muscular tube from mouth
to anus. The lumen is the inner space of the tract. 12e TRA 3; IM CA 3-3
1. The mouth is the beginning of the digestive system. Digestion in the mouth involves mastication
(chewing), the stimulation of taste buds, and swallowing. The pharynx is shared by both the
esophagus and trachea. The epiglottis closes to prevent food from entering the trachea. After
swallowing, the food is called a bolus. Website HN 3-3, 3-4
C. The Muscular Action of Digestion – under autonomic control 10e TRA 23, 24
1. Peristalsis pushes the digestive contents along.
D. The Secretions of Digestion 12e TRA 4, 10e TRA 26
1. Include digestive enzymes that act as catalysts in hydrolysis reactions.
2. Saliva from the salivary glands moistens foods.
E. The Final Stage
1. Energy-yielding nutrients are disassembled for absorption.
II. Absorption 10e TRA 27
A. The enormous surface area of the small intestine facilitates nutrient absorption. Nutrients can be absorbed
through simple diffusion, facilitated diffusion, or active transport.
1. Simple diffusion allows substances to cross a cell membrane without using energy (water and small
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B. Anatomy of the Absorptive System 10e TRA 28
1. Villi are the fingerlike projections within the folds of the small intestine that move in a wave-like
pattern to trap nutrients.
C. A Closer Look at the Intestinal Cells
1. Some portions of the intestine have cells that are specialized to absorb different nutrients.
2. “Food combining,” which emphasizes separating food for digestive purposes, is a myth.
III. The Circulatory System Website HN 3-2
Water-soluble nutrients and small fats are routed to the liver before being transported to the cells. Fat-soluble
nutrients, entering from the lymph, bypass the liver at first and eventually enter the vascular system.
A. The vascular system consists of arteries, capillaries, and veins. 10e TRA 29, 30
1. The hepatic portal vein directs blood from the GI tract to the liver.
B. The lymphatic system consists of one-way vessels to transport fluid.
1. Lymph is a clear, yellowish fluid without red blood cells or platelets that moves through the body by
muscle contractions.
IV. The Health and Regulation of the GI Tract
The principle of homeostasis is important in the functioning of the digestive and absorptive systems. The
body’s hormonal and nervous control systems keep conditions normal.
A. Gastrointestinal Bacteria
1. A healthy GI tract has many different non-disease-causing bacteria known as flora or microflora.
3. Prebiotics are foods that are used as food by intestinal bacteria.
B. Gastrointestinal Hormones and Nerve Pathways 12e TRA 5
1. Hormones act as messengers, and those involved in the GI tract are known as enterogastrones.
2. Gastrin is secreted by the stomach to stimulate the release of hydrochloric acid.
C. The System at Its Best IM WS 3-3
1. A healthy digestive tract is essential.
2. Sleep, physical activity, and state of mind impact gastrointestinal health.
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2. Balance, moderation, variety, and adequacy of meals are important.
V. Highlight: Common Digestive Problems IM CA 3-4; CI Highlight
Many digestive problems reflect hurried lifestyles. Remedies include handling stress, relaxing, getting enough
sleep, and eating in a leisurely manner, in addition to diet strategies.
A. Choking
1. Food becomes lodged in the trachea.
2. The larnyx 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.
D. Constipation
1. Defecation habits are different among people.
2. Many causes are possible.
5. Use of laxatives, enemas, and mineral oil may not be necessary with lifestyle changes.
6. Colonic irrigation is the internal washing of the large intestine and can be hazardous.
7. Strategies
a. High-fiber diet
E. Belching and Gas
1. Strategies
a. Eat slowly.
2. Hiccups are triggered by eating or drinking too fast.
F. Heartburn and “Acid Indigestion”
1. Gastroesophageal reflux is the backward flow of stomach contents into the esophagus.
2. Antacids and acid controllers may help indigestion.
3. Strategies
a. Consume small meals.
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G. Ulcers
1. Peptic ulcers can be gastric or duodenal.
2. Strategies
a. Take prescribed medicine.
Case Study
5
Mary Treat is a 68-year-old woman who reports a recent history of persistent diarrhea and stomach cramps. She is
64 inches tall and her usual body weight is 150 pounds. She takes a daily multi-vitamin supplement and over-the-
counter antacids for occasional heartburn. Her usual diet includes fresh vegetables from her garden and fruit in
season from her fruit tree. She preserves much of her produce so she has year-round fruits and vegetables. Her diet
1. According to information in Highlight 3, what are some general causes of diarrhea?
2. Based on her history, name at least two reasonable explanations for Mary’s sudden onset of diarrhea and
cramps.
3. How would you explain Mary’s symptoms of heartburn?
4. If food poisoning is suspected, what may have been an effect from her regular use of antacids?
5. What immediate treatment would you suggest for her current symptoms?
6. What advice would you offer Mrs. Treat to avoid this type of gastrointestinal discomfort in the future?
7. At what point would you advise her to seek medical care?
Answer Key
1. Food poisoning or other infections; side effect of medications; large intake of the sugar alternative sorbitol and
fat alternative olestra; GI tract disorders such as irritable bowel syndrome or colitis.
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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.
Classroom Activity 3-1: Obtaining Feedback From Students
Objective: Cultivating/maintaining a positive learning environment Class size: Any
Classroom Activity 3-2: Chapter Opening Quiz
Objective: Introduction to digestion Class size: Any
Instructions: As a way of introducing any new chapter, give a quiz to the class. This is a quiz designed to be
projected on an overhead projector. For details, please see Chapter 1, Classroom Activity 1–7.
Classroom Activity 3-3: Demonstration of the Digestive System
Key concept: Visual of size of digestive tract Class size: Any
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
Classroom Activity 3-5: “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.
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Phone a Friend (ask anyone in the classroom). The point scale (see sample) shows the levels of bonus points to be
added to the upcoming exam. If a student becomes a millionaire, he or she receives 100 points (the value of the test).
Point Scale:
$1,000,000
500,000
250,000
125,000
64,000
32,000
16,000
Critical Thinking Questions
7
These questions will also be posted to the book’s website so that students can complete them online and e-mail their
answers to you.
1. Chapter 3 describes in detail how food is processed for use by our bodies. Over your lifetime, you have come
into contact or heard about the following medical issues: painful and bleeding mouth ulcers; stomach cancer;
and gallbladder surgery and removal. To the best of your ability, use the information in Chapter 3 to describe
the types of nutritional and food intake issues that your client might face with one of these
medical/physiological problems. Can you propose some nutrition therapy alternatives?
Answer: In this question, I am looking for the student to use the information from the chapter to make an
educated guess as to how anatomy and physiology will impact nutrient and nutritional status.
2. The process of food digestion through the gastrointestinal tract involves an intricate symphony of interplay
between many systems. A breakdown within any system will influence a client’s ability to absorb nutrients or
eliminate waste. Discuss your concerns as a client’s nutrition expert (RD) if one of the following systems is
dysfunctional: vascular system or absorptive system.
Answer: Vascular System: The vascular system transports nutrients to the cells through the blood after they
have been fully digested and absorbed through the intestinal tract. While there are a variety of vascular issues
that can and may occur, any situation that compromises the vascular system will compromise this system’s
3. In this chapter, the concept of “homeostasis” is discussed in relation to the process of digestion. Describe
homeostasis and then discuss the variety of systems that are part of the digestive homeostatic process. What is
another term that is used for the types of regulation that occur when these systems work together to regulate
digestion in the GI tract?
Answer: (1.) Homeostasis means to maintain the body condition at the same level of or within a narrow range
for appropriate functioning. Homeo is within an organic environment and stasis is to maintain a static
environment.
(2.) Hormones, which are mostly proteins, and the nervous system are needed within the GI system to maintain
homeostasis. For example, enterogastrone is a hormone that inhibits the motility and secretions of the GI tract
when the stomach is full. This is signaled by the nervous system. Reversely, gastrin starts the release of the fluid
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4. In general, we often think that bacteria on or in the body is a “bad” thing. However, we normally retain bacteria
in the intestine for specific reasons. Provide a short discussion of the functions of these bacteria. How can our
dietary intake support the functions of the intestinal bacteria?
Answer: The bacteria in the intestine are called microflora and help to digest foodstuffs such as the dietary
fibers and complex proteins in the intestine. They are very important in creating the homeostatic environment
that is critical to the normal functioning of the GI tract. GI bacteria are not only able to break down nutritional
5. After studying the GI system in Chapter 3, you can appreciate how complex and well organized this system is
as a whole, and how well it functions in digesting and absorbing the food we eat to allow it to be used for
energy, metabolic reactions, tissue growth, and repair. We have discussed some of the ways that the GI system
may break down and impact nutrient absorption and use. However, even in a healthy individual, there are many
factors that one must keep in mind that can optimize the functioning of the GI system, and therefore nutrient
digestion, absorption, and use. Discuss some of the factors that you would assess in a healthy client who came
to you concerned about maximizing their nutritional status and nutrient absorption.
Answer: Clients free of medical health issues can still suffer from digestive problems through poor lifestyle
choices or conditions. Our lifestyles are stressful; many individuals commute long distances to work or work
many different jobs, and some have no job and worry about where their next meal will come from. Exercise
6. Highlight #3 suggests many common and simple solutions to common digestive problems. These problems are
quite often observed by health professionals in the course of caring for patients in a hospital or clinic setting.
The RD must retain knowledge and multiple skills, such as those discussed in this highlight, to best care for
their patients/clients, sometimes referred to as enhanced or multiskilling in the dietetics practice. Suggest
additional solutions for the digestive problems outlined in Highlight 3 that were not covered. Also suggest other
areas that are not normally considered part of dietetics education that may enhance the practice role of a
dietitian and increase the visibility of their practice and the profession.
Answer: Highlight #3 does an excellent job of reviewing some of the common digestive problems that many
clients will experience at some point in their lifetime. Most often, clients look to their physician or nurse for a
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Vomiting: As indicated, there are many reasons for vomiting. What is important to observe with the vomiting
client is their hydration status. For appropriate age groups (teen and young adult), assess for eating disorders. As
indicated, in babies and in the elderly, excessive vomiting can be very serious. In both of these populations,
excessive fluid losses can lead to deadly electrolyte imbalances very quickly. Therefore, both the very young
and the very elderly should be transported to a medical facility quickly in these circumstances.
Any young or middle-aged adult that is assessed for an eating disorder (by teeth erosion, mouth sores, etc.)
should be referred to a psychologist or an agency that can provide appropriate support for psychological
counseling.
Diarrhea: Like vomiting, diarrhea can result in dehydration and for many reasons. The goal is always to find the
cause of diarrhea prior to intervening. Slowing down the transit of nutrients through the GI tract is important for
their absorption; therefore, it is very important to control diarrhea when medically possible. After a client has
been cleared of any medical issues, it is important to remember that the GI tract can be very sensitive to the
individual’s stress. It is important to assist each client in relaxing through their medical procedures and to keep
them as fully informed as possible. Clients can benefit from counseling, stress management training, and
relaxation therapy. Dietitians that are not trained in these skills should keep a listing of local professionals to
refer their clients to when needed.
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IM Worksheet Answer Key
Worksheet 3-1: Chapter 3 Crossword Puzzle
Worksheet 3-2: Digestion, Absorption, & Transport—DAT
For digestion/enzyme activation and absorption columns, see Figure 3-8. Transport: proteins, water-soluble
vitamins, minerals and water are released directly into the bloodstream, whereas lipids and fat-soluble vitamins are
first released into the lymphatic system. Hormonal regulation: cholecystokinin for lipids and proteins.
Worksheet 3-3: Food Habits, Digestion, and Absorption
Worksheet 3-4: Further Exploration on Digestion (Internet Exercise)
Canadian Information
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Highlight 3: Common Digestive Problems
Canadian students who are interested in more information about Canadian research and food products available in
Canada related to digestive problems can search the following web sites:
Shelley Case, a registered dietitian, has published the Gluten-Free Diet: A Comprehensive Resource Guide (2008), a
guide that is held in high regard by dietitians.
9
Findings from a recent qualitative study
10
of women with irritable bowel syndrome and inflammatory bowel disease
revealed women commonly experience frustration when seeking to determine triggers for symptoms and
experimenting with behaviours (including food choices) that may relieve the symptoms.
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Results from the recently conducted Canadian Celiac Health Survey
11
indicate medical conditions often occur with
celiac disease and food labeling requirements need to be improved to assist people with celiac disease to better
manage their symptoms.
Canadians diagnosed with celiac disease are able to claim incremental costs associated with purchasing gluten-free
the former Irritable Bowel Syndrome Association into its organization. The web site of this newly expanded
organization offers self-help and support group information, web-based brochures, book reviews, and other
resources and information on irritable bowel syndrome.
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Worksheet 3-1: Chapter 3 Crossword Puzzle
Across
Down
3. the food pipe; the conduit from the mouth to the
stomach
5. a narrow blind sac extending from the beginning of
the colon that stores lymph cells
7. the organ that manufactures bile and is the first to
1. cartilage in the throat that guards the entrance to the
trachea and prevents fluid or food from entering it
when a person swallows
2. the lower portion of the intestine that completes the
digestive process and consists of four segments
1 2
3 4
5 6
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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
Minerals
Water
1. What dietary factors not listed above influence the processes of DAT?
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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 depends 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.
h. Create a meal using citrus fruits and meat.
i. Tackle family problems at the dinner table.
2. Do you experience GI distress regularly?
d. Eat a low-fiber diet.
g. Eat quickly and then lie down to rest.
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Worksheet 3-4: Further Exploration on Digestion (Internet Exercise)
Go to this website to answer questions 1-10: http://digestive.niddk.nih.gov/ddiseases/pubs/yrdd/.
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.
a. True
b. False
4. Which of the following statements regarding factors affecting emptying of the stomach is/are true? Select all
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.
a. True
b. False
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.
9. Which of the following hormones regulate appetite?
a. Ghrelin and peptide YY
b. Gastrin and peptide YY
c. Secretin, CCK, and gastrin
d. Secretin and ghrelin
10. Intrinsic nerves release acetylcholine and adrenaline.
a. True
b. False
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Handout 3-1: Examples of Hormonal Feedback Loops