15
Instructor’s Manual for
The Digestive System
LEARNING OBJECTIVES WITH RATIONALE
After completing this chapter the student will be able to:
1. List in sequence each of the component parts or segments of the alimentary canal from the mouth to
the anus and identify the accessory organs of digestion.
The component parts of the alimentary canal from mouth to anus are mouth, pharynx (throat),
esophagus, stomach, small intestine (duodenum, jejunum, ileum), and large intestine (cecum, colon,
rectum, anal canal).
Accessory organs of digestion include teeth and tongue, salivary glands (parotid, submandibular,
sublingual), gallbladder, pancreas, and vermiform appendix.
2. List and describe the four layers of the wall of the alimentary canal. Compare the lining layer in the
esophagus, stomach, small intestine, and large intestine.
The four layers that make up the wall of the alimentary canal include (from the inside layer
moving out) mucosa or mucous membrane, submucosa, muscular coat or muscularis, and adventitia
or serosa. Although the same four tissue coats form every organ of the alimentary tract, their
structures vary in different organs. The mucosa of the esophagus is composed of tough, stratified,
abrasion-resistant epithelium. The mucosa of the remainder of the tract is a delicate layer of simple
columnar epithelium designed for absorption. In the stomach region, the mucosa is lined with
thousands of microscopic gastric glands that secrete gastric juice and hydrochloric acid. When the
stomach is empty, its mucous lining lies in folds called rugae. The mucous lining of the small
intestine, like that of the stomach, contains thousands of microscopic glands. These are called
intestinal glands, and they secrete intestinal digestive juice. The intestinal lining is made up of
multiple circular folds called plicae. These folds are covered with thousands of tiny “fingers” called
villi. Inside each villus lies a rich network of blood capillaries that absorb the products of digestion. No
villi are present in the mucosa of the large intestine. As a result, less surface area is available for
absorption, and the efficiency and speed of movement of substances through the wall of the large
intestine are much lower than in the small intestine.
The submucosa is a connective tissue layer just below the mucosa. It contains nerves and blood
vessels. The two layers of muscle tissue called the muscularis move food, by means of contraction in
a motion called peristalsis, through the digestive tube. Contraction also mixes food with digestive
juices and mechanically breaks down food. The serosa is the outermost covering or coat of the
digestive tube. In the abdominal cavity it is composed of visceral peritoneum. The intestines are
anchored to the posterior wall of the abdominal cavity by a large double fold of peritoneal tissue
called the mesentery.
3. Discuss the basics of protein, fat, and carbohydrate digestion and give the end products of each of
these processes.
Very little carbohydrate digestion occurs before food reaches the small intestine. Salivary
amylase found in saliva begins the chemical breakdown of carbohydrates, but it has little time to work
because food is usually swallowed quite fast. Gastric juices contain no carbohydrate-digesting
enzymes. Once food reaches the small intestine, pancreatic and intestinal juice enzymes digest
starches and sugars. A pancreatic enzyme (amylase) starts the process by changing polysaccharides
such as starches into disaccharides (double sugars). Three intestinal enzymes—maltase, sucrase,
and lactase—digest disaccharides by changing them into monosaccharides (simple sugars). Maltase
digests maltose (malt sugar), sucrase digests sucrose (cane sugar), and lactase digests lactose (milk
sugar). The end products of carbohydrate digestion are simple sugars (monosaccharides). The most
abundant monosaccharide is glucose.
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Structure & Function of the Body, 14th ed.
Thibodeau & Patton
634 Chapter 15  The Digestive System _________________________________________________________
Protein digestion starts in the stomach. Pepsin, an enzyme found in gastric juice, causes the
giant protein molecules to break up into simpler compounds. Then in the intestine other enzymes
(trypsin in pancreatic juice and peptidase in intestinal juice) complete protein digestion. Every protein
molecule is made up of many amino acids joined together. When enzymes have split up the large
protein molecule into its separate amino acids, protein digestion is completed. The end products of
protein digestion are amino acids.
Fat digestion may begin in the stomach when an enzyme called gastric lipase is secreted.
However, most fats go undigested, until they are emulsified by bile in the duodenum of the small
intestine. After this takes place, the pancreatic enzyme (steapsin or pancreatic lipase) splits fat
molecules into their building blocks, fatty acids and glycerol. The end products of fat digestion are
fatty acids and glycerol.
4. Define and contrast mechanical and chemical digestion.
Mechanical digestion breaks food into tiny particles, mixes these particles with digestive juices,
moves them along the alimentary canal, and finally eliminates the digestive wastes from the body.
Chewing (mastication), swallowing (deglutition), peristalsis, and defecation are the main processes of
mechanical digestion.
Chemical digestion breaks down large, nonabsorbable food molecules into smaller, absorbable
molecules that are able to pass through the intestinal mucosa into blood and lymph. Chemical
digestion includes the chemical reactions catalyzed by enzymes in saliva, gastric juice, pancreatic
juice, and intestinal juice.
5. Define peristalsis, bolus, chyme, jaundice, ulcer, and diarrhea.
Peristalsis—the movement of food through the digestive tube; brought about due to contractions
of the muscularis or muscular coat.
Bolus—a small rounded mass created after food has been chewed; allows food to be swallowed.
Chyme—a semisolid mixture that is food mixed thoroughly with gastric juice.
Jaundice—a yellowish skin discoloration that occurs when excessive amounts of bile are
absorbed into the blood.
Ulcer—an open wound or sore in an area of the digestive system that is acted upon by acid
gastric juice. Two common sites for ulcers are the stomach and the duodenum. Left untreated, ulcers
cause persistent pain and they may actually perforate the wall of the digestive tube, causing
hemorrhage and inflammation of the abdominal cavity.
Diarrhea—a state in which fecal material is liquid.
LECTURE OUTLINE
I.
OVERVIEW OF THEDIGESTIVE SYSTEM (Figure
15-1 and Table 15-1)
A. Irregular tube called alimentary canal or
gastrointestinal (GI) tract and accessory organs
of digestion
B. Food must first be digested, then absorbed, and
later metabolized
II.
PRIMARY MECHANISMS OF THE DIGESTIVE
SYSTEM (Table 15-2)
A. Ingestion—complex foods taken into the GI tract
B. Digestion—group of processes that break
complex nutrients into simpler ones
1. Mechanical digestion- breakup of large
chunks of food into smaller bits
2. Chemical digestion- breaks large molecules
into smaller ones
C. Motility—a number of GI movements resulting
from muscular contraction
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INSTRUCTOR'S NOTES
Structure & Function of the Body, 14th ed.
Thibodeau & Patton
_________________________________________________________ Chapter 15  The Digestive System
LECTURE OUTLINE
D.
E.
F.
635
INSTRUCTOR'S NOTES
Secretion—release of digestive juices and
hormones that facilitate digestion
Absorption—movement of digested nutrients into
the internal environment of the body
Regulation—neural, hormonal and other
mechanisms that regulate digestive activity
III.
WALL OF THE DIGESTIVE TRACT (Figure 15-2)
The wall of the digestive tube is formed by four layers
of tissue:
A. Mucosa—type varies depending on GI location
(tough and stratified or delicate and simple
epithelium); mucus production
B. Submucosa—connective tissue layer
C. Muscularis—circular, longitudinal, and oblique (in
stomach) layers of smooth muscle; important in
GI motility
1. Peristalsis— “wavelike” movement pushes
food down the tract (Figure 15-3)
2. Segmentation – “back and forth” movement
(Figure 15-4)
D. Serosa—serous membrane that covers the
outside of abdominal organs; it attaches the
digestive tract to the wall of the abdominopelvic
cavity by forming folds called mesenteries
IV.
MOUTH
A. Roof—formed by hard palate (parts of maxillary
and palatine bones) and soft palate, an archshaped muscle separating mouth from pharynx;
uvula, a downward projection of soft palate
(Figure 15-5)
B. Floor—formed by tongue (skeletal muscle
covered by mucous membrane) and its muscles;
papillae, small elevations on mucosa of tongue;
taste buds, found in many papillae; lingual
frenulum, fold of mucous membrane that helps
anchor tongue to floor of mouth (Figure 15-5)
V.
TEETH
A. Structures of a typical tooth
1. Crown, visible portion of the tooth, covered
by enamel—the hardest tissue in the body
2. Neck, joins the crown of the tooth to the root,
surrounded by pink gingival tissue (gum
tissue)
3. Root, fits into the bony socket and anchors
the tooth to the bone with a fibrous
periodontal membrane (Figure 15-6)
B. Names of teeth—incisors; cuspids, also called
canines or “eyeteeth;” bicuspids, also called
premolars; tricuspids, also called molars
C. Twenty teeth in temporary set (also called
deciduous); average age for cutting first tooth
about 6 months; set complete at about 2 years of
age
D. Thirty-two teeth in permanent set; 6 years about
Copyright © 2012 by Elsevier Inc. All rights reserved.
Structure & Function of the Body, 14th ed.
Thibodeau & Patton
636 Chapter 15  The Digestive System _________________________________________________________
LECTURE OUTLINE
INSTRUCTOR'S NOTES
average age for starting to cut first permanent
tooth; set complete usually between ages of 17
and 24 years (Figure 15-5)
VI.
SALIVARY GLANDS (Figure 15-7)
A. Saliva- exocrine gland secretion flows into ducts
1. Serous type—watery and contains enzymes
(salivary amylase) but no mucus
a. produced by serous type secretory cells
(Figure 15-7, B)
2. Mucus type—thick, slippery and contains
mucus but no enzymes
a. lubricates food during mastication
b. produced by mucus type secretory cells
(Figure 15-7, B)
B. Parotid glands (Figure 15-7)—largest of the
salivary glands; lie just below and in front of each
ear at the angle of the jaw; secrete saliva
containing mucus and salivary amylase into
ducts to be conveyed to the mouth cavity
C. Submandibular glands—ducts open into the
mouth on either side of the lingual frenulum;
produces both serous and mucus type saliva
(Figure 15-7, B)
D. Sublingual glands—multiple ducts open into the
floor of the mouth; produce only mucus type
saliva
VII.
PHARYNX—tubelike structure of muscle lined with
mucous membrane; functions are part of both
respiratory and digestive systems (see three divisions
as described in Chapter 14)
A. Anatomical components: nasopharynx,
oropharynx, laryngopharynx (see anatomical
description Chapter 14 and Figure 14-4)
B. Oropharynx most involved segment in digestive
process of swallowing or deglutition
1. Regulation of deglutition movements via
motor cortex of cerebrum (voluntary) and
“deglutition center” of brainstem (involuntary)
VIII.
ESOPHAGUS—muscular tube lined with mucous
membrane that connects the pharynx with the
stomach; food enters stomach by passing through
lower esophageal sphincter (LES) or cardiac
sphincter
IX.
STOMACH (Figure 15-8) Lies in the upper part of the
abdominal cavity just under the diaphragm; serves as
a pouch to receive chewed food from the esophagus
A. Size—expands considerably after large meal;
about size of large sausage when empty
B. Cardiac sphincter—ring of muscle tissue at the
end of esophagus; keeps food mixed with gastric
acids from reentering the esophagus
C. Pylorus—lower part of stomach; pyloric sphincter
muscle closes opening of pylorus into duodenum
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Structure & Function of the Body, 14th ed.
Thibodeau & Patton
_________________________________________________________ Chapter 15  The Digestive System
LECTURE OUTLINE
D.
E.
637
INSTRUCTOR'S NOTES
Wall—many smooth muscle fibers; contractions
produce churning movements (peristalsis)
Lining—mucous membrane; many microscopic
glands that secrete gastric juice and hydrochloric
acid into stomach; mucous membrane lies in
folds (rugae) when stomach is empty
X.
SMALL INTESTINE (Figure 15-9)
A. Size—about 7 meters (20 feet) long but only 2
cm or so in diameter
B. Divisions
1. Duodenum
2. Jejunum
3. Ileum
C. Wall—contains smooth muscle fibers that
contract to produce peristalsis and segmentation
movements
D. Lining—mucous membrane; many microscopic
glands (intestinal glands) secrete intestinal juice;
villi (microscopic finger-shaped projections from
surface of mucosa into intestinal cavity) contain
blood capillaries and lymph lacteals for nutrient
absorption; each villus is covered by microvilli
that further increase the surface area for
absorption of nutrients
XI.
LIVER AND GALLBLADDER
A. Size and location—liver is largest gland; fills
upper right section of abdominal cavity and
extends over into left side
B. Liver secretes bile which contains significant
quantities of cholesterol and bile salts that act as
detergents to emulsify fat; bile that is eliminated
in feces also carries cholesterol from the body
C. Ducts (Figure 15-10)
1. Hepatic—drains bile from liver
2. Cystic—duct by which bile enters and leaves
gallbladder
3. Common bile—formed by union of hepatic
and cystic ducts; drains bile from hepatic or
cystic ducts into duodenum
4. Release of bile—fat in chyme stimulates
release of cholecystokinin which contracts
the gallbladder to release bile into the
duodenum
D. Gallbladder
1. Location—undersurface of the liver
2. Function—concentrates and stores bile
produced in the liver
XII.
PANCREAS
A. Location—behind stomach
B. Functions—exocrine and endocrine gland
1. Pancreatic cells secrete pancreatic juice into
pancreatic ducts; main duct empties into
duodenum (exocrine function); contains
enzymes to digest all three major kinds of
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638 Chapter 15  The Digestive System _________________________________________________________
LECTURE OUTLINE
2.
INSTRUCTOR'S NOTES
food
Pancreatic islets (islets of Langerhans)—
cells not connected with pancreatic ducts;
secretes two hormones: glucagon (alpha
cells) and insulin (beta cells) into the blood
XIII.
LARGE INTESTINE (Figure 15-12)
A. Divisions
1. Cecum: ileocecal valve is connection with
the small intestine; consistency of chyme
changes with the reabsorption of water and
salts; now called feces; presence of bacteria
releases additional nutrients from cellulose
and other fibers
2. Colon—ascending, transverse, descending,
and sigmoid
3. Rectum
B. Opening to exterior—anus
C. Wall—contains smooth muscle fibers that
contract to produce churning, peristalsis, and
defecation
D. Lining—mucous membrane; absorption of water,
salts, vitamins; no villi so much less surface area
XIV.
APPENDIX Blind tube off cecum; no important
digestive functions in humans; “vermiform” means
shaped like a worm
XV.
PERITONEUM (Figure 15-14)
A. Definitions—peritoneum, continuous serous
membrane lining abdominal cavity and covering
abdominal organs; parietal layer of peritoneum
lines abdominal cavity; visceral layer of
peritoneum covers abdominal organs; peritoneal
space lies between parietal and visceral layers
with enough fluid between them to keep them
moist and enable them to slide freely against
each other during breathing and digestion
B. Extensions—largest ones are the mesentery and
greater omentum; mesentery is extension of
parietal peritoneum, which attaches most of small
intestine to posterior abdominal wall; greater
omentum, or “lace apron,” hangs down from
lower edge of stomach and transverse colon over
intestines
XVI.
DIGESTION (Table 15-3) Physical and chemical
changes to food to prepare nutrients to be absorbed
and used by cells
A. Mechanical digestion—chewing, swallowing, and
peristalsis break food into tiny particles, mix them
well with digestive juices, and move them along
the digestive tract
B. Chemical digestion—breaks up large food
molecules into compounds having smaller
molecules; brought about by digestive enzymes
C. Carbohydrate digestion—mainly in small intestine
Copyright © 2012 by Elsevier Inc. All rights reserved.
Structure & Function of the Body, 14th ed.
Thibodeau & Patton
_________________________________________________________ Chapter 15  The Digestive System
LECTURE OUTLINE
639
INSTRUCTOR'S NOTES
1.
D.
E.
XVII.
Pancreatic amylase—changes
polysaccharides (starches) into
disaccharides
2. Intestinal juice enzymes
a. Maltase—changes maltose (malt sugar)
into glucose
b. Sucrase—changes sucrose (ordinary
cane sugar or table sugar) into glucose
c. Lactase—changes lactose (milk sugar)
to glucose
Protein digestion—starts in stomach; completed
in small intestine
1. Gastric juice enzymes, renin and pepsin,
partially digest proteins by causing the giant
protein molecules to break up into somewhat
simpler compounds
2. Pancreatic enzyme, trypsin, completes
digestion of proteins to amino acids
3. Intestinal enzymes, peptidases, complete
digestion of partially digested proteins to
amino acids
Fat digestion
1. Bile contains no enzymes but emulsifies fats
(breaks fat droplets into very small droplets)
2. Pancreatic lipase changes emulsified fats to
fatty acids and glycerol in small intestine
ABSORPTION
A. Meaning—digested food moves from intestine
into blood or lymph
B. Where absorption occurs—foods and most water
from small intestine through villi; some water also
absorbed from large intestine
C. Surface area—new studies use fractal geometry
to demonstrate the seemingly infinite surface
area of the small intestine (Figure 15-8); the
plicae (folds) have villi, the villi have microvilli,
and the microvilli have bumps that further
increase the surface area
CLASSROOM APPLICATION
The following questions can be used as individual assignments or for small-group discussion. Note: to
copy the questions, cover the answers with a blank sheet of paper and print, thus leaving space for
answers or note-taking.
1. Mr. Harrison, your neighbor, has complained of heartburn and indigestion for over 6 months. He
recently went to his physician and was told he has a hiatal hernia. He asks you the following
questions.
(a) “What is a hiatal hernia and what has taken place physically?”
(b) “My doctor told me I have gastroesophageal reflux disease. Can you explain this disease to me?”
What symptoms are usually present?
(c) He shows you a prescription for Prilosec. Mr. Harrison tells you he is unfamiliar with the
prescribed drug. You offer to stop by the pharmacy and obtain a printout of information
concerning the medication prescribed by his doctor.
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Structure & Function of the Body, 14th ed.
Thibodeau & Patton
640 Chapter 15  The Digestive System _________________________________________________________
Write your responses to the above questions. Also obtain a pharmacy printout of information on
the following medications: Tagamet, Zantac, Pepcid, and Prilosec.
Answers: (a) A hiatal hernia is a condition in which the diaphragm, through which the esophagus
passes, is enlarged or stretched enabling a portion of the stomach or lower end of the esophagus to
extend upward into the chest cavity. Individuals suffering from a hiatal hernia complain most often of
heartburn and indigestion. (b) Gastroesophageal reflux disease (GERD) occurs when there is a
backflow of stomach contents into the esophagus, which is often the result of a hiatal hernia. Gastric
juices that are highly acidic produce burning in the esophagus, and pain may be experienced in the
chest area as well. Antacids are often prescribed. (c) Share with the class the information you have
obtained from a pharmacy concerning antacids often prescribed for GERD.
2. Design a poster depicting the alimentary canal. Label all of the areas and describe how food passes
through each area.
Answer: The alimentary canal or digestive tract extends from the mouth to the anus and is lined
with mucous membrane. It is composed of the mouth, pharynx, esophagus, stomach, small intestines
(duodenum, jejunum, ileum), large intestines (cecum, colon), the colon (ascending colon, transverse
colon, descending colon, sigmoid colon), rectum, and anal canal.
LAB ACTIVITIES
1. Have students dissect a rat to locate the esophagus, stomach, intestines, liver, and pancreas.
2. Have students examine prepared slides of the stomach and intestine to identify the mucosa of each.
3. Display for the students gallstones obtained from a local hospital as well as information concerning
the chemical makeup of the stones. Have the students research the physiological process by which
stones develop.
4. Have students use a mirror and tongue depressor to locate the incisors, cuspids, bicuspids, and
molars in their mouths.
5. Have students identify the peritoneum and its folds (omentum, mesentery) in a dissected rat or cat.
6. Have students test the chemical makeup of various food types by using:
a. Benedict’s solution to identify sugars
b. Lugol’s solution to identify starches
PRACTICAL/CREATIVE LEARNING ACTIVITIES
1. Statistics have shown that about 1 in 10 individuals in the United States suffers from ulcers. One of
the discoveries concerning gastric and duodenal ulcers is that they result from an infection caused by
Helicobacter pylori (H. pylori).
Investigate the mode of treatment currently used in the management of bacteria-caused ulcers.
Design a poster with the following information: name and define disease, describe common
symptoms. Look up and explain triple therapy, and the current results of this therapy.
2. With a lab partner, have students listen with a stethoscope as their partner swallows a mouthful or
two of water. Instruct them to place the stethoscope below the xiphoid process, approximately 1 inch
below and slightly to the left. Explain there should be two distinct sounds, one when the water
reaches the cardioesophageal sphincter and one when the peristaltic waves begin and the sphincter
opens.
Ask students, “How long does it take for the water to reach the sphincter and for the sphincter to
open?” (It should be a matter of seconds.) Have students record their answers and compare the
timing with other class members.
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Structure & Function of the Body, 14th ed.
Thibodeau & Patton
_________________________________________________________ Chapter 15  The Digestive System
641
3. On a model of the human skull, have students identify the four types of teeth: the incisors, canines,
premolars, and molars.
4. Have students make a chart listing the pancreatic enzymes and explaining how they aid in the
digestion of fats, proteins, and carbohydrates.
ANSWERS TO CHAPTER 15 TEXTBOOK QUESTIONS
Review Questions
1. Name and describe the four layers of the wall of the gastrointestinal tract.
Answer: a. The mucosa or mucous membrane of the esophagus is composed of tough stratified
epithelium. The mucosa of the lower part of the tract is made of simple columnar epithelium that is
designed for absorption and secretion. b. Submucosa is connective tissue that lies just below the
mucosa. It contains blood vessels and nerves. c. Muscularis is composed of two layers of muscle
tissue. This muscle tissue plays an important part in the digestive process. Wavelike contractions of
the muscular tissue called peristalsis move food and digestive juices through the digestive tract. d.
Serosa is the outer covering of the digestive tube. In the abdominal cavity it is composed of parietal
peritoneum.
2. What is the function of the uvula and soft palate?
Answer: The soft palate is situated above the posterior portion of the mouth. It consists of soft
muscular tissue that hangs down from the center of the soft palate, appearing somewhat coneshaped. The soft palate and the uvula together prevent liquid and food from entering the nasal
cavities.
3. Explain the function of the different types of teeth.
Answer: a. Incisors have a sharp cutting function; found in the four front teeth in each jaw of an
adult. b. Canine teeth, sometimes called cuspids, tear food as it is being eaten or chewed. c.
Premolars or bicuspids, as well as molars or tricuspids, have large flat surfaces designed to grind or
crush food as it is broken down in the mouth.
4. Describe the three main parts of a tooth.
Answer: a. The crown of the tooth is the area exposed and visible in the mouth; it is covered by
enamel. b. The neck of the tooth is the narrow area surrounded by the gum tissue. c. The root fits
into the socket of the upper and lower jaws.
5. Name the three pairs of salivary glands and describe where the duct from each enters the mouth.
Answer: a. Parotid glands are the largest of the salivary glands; they lie just below and in front of
each ear. The opening of the parotid ducts can be seen inside the cheek area opposite the second
molar tooth on each side of the upper jaw. b. The submandibular glands open into the mouth on
either side of the frenulum, which is a thin membrane that attaches the tongue to the floor of the
mouth. c. The sublingual glands open into the floor of the mouth.
6. What are the functions of the cardiac and pyloric sphincter muscles?
Answer: Food enters the stomach through the cardiac sphincter located at the end of the
esophagus. The cardiac sphincter prevents food from reentering the esophagus as the stomach
contracts. The pyloric sphincter prevents food from leaving the stomach and entering the
duodenum. The smooth muscle fibers of the sphincter stay closed most of the time, thereby holding
partially digested food in the stomach, keeping the pylorus closed.
7. Define peristalsis.
Answer: Wavelike, rhythmic contractions of the stomach and intestines that move food material
along the digestive tract.
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Structure & Function of the Body, 14th ed.
Thibodeau & Patton
642 Chapter 15  The Digestive System _________________________________________________________
8. Explain how bile from the liver and gallbladder reaches the small intestine. What is the function of
cholecystokinin?
Answer: The cystic duct drains bile from the gallbladder, whereas the common hepatic duct
drains bile from the liver. The cystic duct and the common hepatic duct join and form the common bile
duct, which drain into the small intestines. Cholecystokinin is a hormone secreted by the intestinal
mucosa of the duodenum, which then stimulates the gallbladder to release bile into the duodenum.
9. What is contained in pancreatic juice?
Answer: Pancreatic juice contains enzymes that digest all three kinds of food, sodium
bicarbonate, and an alkaline substance that neutralizes hydrochloric acid.
10. What do the bacteria in the large intestine contribute to the body?
Answer: Material that is not digested in the small intestines is acted upon by the bacteria in the
large intestines. The result being that additional nutrients may be released from cellulose and other
fibers and then absorbed. Bacteria in the large intestines also are responsible for the synthesis of
vitamin K and for the production of some B-complex vitamins that can then be absorbed into the
blood.
11. List the seven subdivisions of the large intestine.
Answer: Cecum, ascending colon, transverse colon, descending colon, sigmoid colon, rectum,
anal canal
12. Describe the mesentery and the greater omentum.
Answer: Mesentery is the large double fold of peritoneal tissue that holds the loops of the
digestive tract to the posterior wall of the abdominal cavity. The greater omentum is the pouchlike
extension of the visceral peritoneum from the lower edge of the stomach, part of the duodenum, and
the transverse colon.
13. Differentiate between mechanical digestion and chemical digestion.
Answer: The main processes involved in mechanical digestion are chewing, swallowing,
peristalsis, and defecation. Chemical digestion consists of numerous chemical reactions catalyzed
by enzymes in saliva, gastric juices, pancreatic juice, and intestinal juices, which then break down
food molecules that pass through the intestinal mucosa into the blood and lymph systems.
14. Briefly describe the process of carbohydrate digestion.
Answer: Little digestion of carbohydrates occurs prior to reaching the small intestines. Once in
the small intestines, the pancreatic enzyme amylase changes starches into double sugar, mainly
maltose. Intestinal enzymes—maltase, sucrase, and lactase—change double sugars into simple
sugars, mainly glucose. The end product of carbohydrate digestion is simple sugars, primarily
glucose.
15. Briefly describe the process of fat digestion.
Answer: Most fats are undigested until emulsification by bile in the duodenum, after which
pancreatic lipase splits fat molecules into fatty acids and glycerol. The end product of fat digestion is
fatty acids and glycerol.
16. Briefly describe the process of protein digestion.
Answer: Protein digestion starts in the stomach. Two enzymes, renin and pepsin, are in the
gastric juices of the stomach; these cause large protein molecules to break into smaller compounds.
Pepsinogen, also in gastric juice, is converted into active “pepsin enzyme” by hydrochloric acid. In the
intestines, trypsin in pancreatic juice and peptidases in intestinal juice complete protein digestion. The
end product of protein digestion is amino acids.
17. Explain the process of absorption. What function do the lacteals have in absorption?
Answer: After digestion, absorption of food takes place. Absorption is a process by which
molecules of amino acids, glucose, fatty acids, and glycerol go from inside the intestines into the
circulation body fluids.
Copyright © 2012 by Elsevier Inc. All rights reserved.
Structure & Function of the Body, 14th ed.
Thibodeau & Patton
_________________________________________________________ Chapter 15  The Digestive System
643
Lacteals are lymph vessels located in each villi of the intestines; they serve to absorb fat from the
chyme, which passes through the small intestines.
Critical Thinking Questions
18. What structures in the small intestine increase the internal surface area? What advantage is gained to
this increase in surface area?
Answer: The structures within the lining of the small intestine are called plicae, which are
arranged into multiple circular folds covered with thousands of villi. Inside each villus are blood
capillaries that absorb the products of carbohydrate and protein digestion.
19. Bile does not cause a chemical change. What is the effect of bile on fat and why does this make fat
digestion more efficient?
Answer: Bile mechanically breaks up or emulsifies large globules of fat into smaller particles.
This emulsification function of bile increases the surface area for digestion, making the process more
efficient.
20. Some people are lactose intolerant. This means they are unable to digest lactose sugar. What
enzyme is probably not functioning properly and what types of food should these people try to avoid?
Answer: A deficiency of the enzyme lactase is necessary for the absorption of lactose from the
intestinal tract. These individuals should avoid foods that contain lactose such as milk and milk
products.
Copyright © 2012 by Elsevier Inc. All rights reserved.
Structure & Function of the Body, 14th ed.
Thibodeau & Patton
644 Chapter 15  The Digestive System _________________________________________________________
15
Instructor’s Manual for
The Digestive System
STUDENT ASSIGNMENT
Multiple Choice
Christie is 2 months old. She is unable to keep her formula down. Her mother notices that not only does
she spit up after feeding, but that the milk is curdled and undigested.
1. What diagnosis is the doctor likely to make?
A. Christie dislikes the milk she is being fed.
B. She probably has pylorospasm.
C. The mother is advised to hold Christie in a more upright position when feeding her.
D. Tonsillitis prevents Christie from swallowing properly.
2. The doctor has ordered oral rehydration for Christie because she is dehydrated. He has prescribed a
prepared solution that contains which of the following ingredients?
A. water and sugar
B. protein and fat
C. sugar and salt
D. none of the above
3. Janice Kafer is a 36-year-old professional nurse in charge of a very busy pediatric unit. She works
long hours under demanding and stressful circumstances. She reveals to her physician that she
suffers frequent episodes of stomach pain. After an extensive exam and x-rays he tells her that the
first part of the small intestine is inflamed causing her stomach pain. What is this part of the small
intestine called?
A. duodenum
B. jejunum
C. esophagus
D. pylori orifice
4. The doctor also felt Ms. Kafer had an over production of acid. What is this acid called?
A. submucosa
B. cecum
C. ileocecal
D. hydrochloric
5. Mr. Bell, age 51, has noticed blood in his feces. After testing, the doctor informed him of a tumor in
the last part of the colon. What is this S-shaped part of the colon called?
A. sigmoid
B. small intestine
C. duodenum
D. rugae
6. Duodenal ulcers appear in which of the following?
A. stomach
B. small intestine
C. large intestine
D. esophagus
Copyright © 2012 by Elsevier Inc. All rights reserved.
Structure & Function of the Body, 14th ed.
Thibodeau & Patton
_________________________________________________________ Chapter 15  The Digestive System
645
7. What is the portion of the peritoneum that holds the intestinal loops in place called?
A. omentum
B. mesentery
C. peritoneal cavity
D. ligament
8. A product of digestion called chyme is formed in which of the following?
A. esophagus
B. small intestine
C. stomach
D. large intestine
9. The enzyme pepsin is concerned primarily with the digestion of which of the following?
A. sugars
B. starches
C. proteins
D. fats
10. The enzyme amylase converts which of the following?
A. starches to sugars
B. sugars to starches
C. proteins to amino acids
D. fatty acids and glycerols to fats
Completion
Complete the following statements using the terms listed below.
A. Ileum
M. Pyloric sphincter
B. Amylase
N. Sigmoid colon
C. Muscular coat
O. Canines
D. Metabolism
P. Amino acids
E. Cholecystokinin
Q. Duodenum
F. Molars
R. Jejunum
G. Cardiac sphincter
S. Premolars
H. Digestion
T. Mucosa
I. Incisors
U. Submucosa
J. Greater omentum
V. Cecum
K. Absorption
W. Bile
L. Adventitia
X. Serosa
11. The S-shaped portion of the colon is called _____.
12. The portion of the peritoneum that descends from the stomach and the transverse colon to form a
lacy apron of fat over the intestines is called the _____.
13. The “building blocks” of protein molecules are _____.
14. The small intestine is made up of three sections called _____, _____, and _____.
15. Fats that enter into the digestive tract are emulsified when they are acted upon by a substance called
_____.
16. Foods undergo three kinds of processing in the body: _____, _____, and _____.
17. Fats in the chyme stimulate the secretion of _____, which stimulates contraction of the gallbladder to
release bile.
Copyright © 2012 by Elsevier Inc. All rights reserved.
Structure & Function of the Body, 14th ed.
Thibodeau & Patton
646 Chapter 15  The Digestive System _________________________________________________________
18. The four tissue layers that make up the wall of the digestive tract are _____, _____, _____, and
_____.
19. Food enters the stomach by passing through a muscular structure at the end of the esophagus. This
structure is called the _____.
20. The four major types of teeth found in the human mouth are _____, _____, _____, and _____.
Matching
Select the most correct answer from Column B for each item in Column A. (Only one answer is correct for
each.)
Column A
Column B
_____ 21. Salivary gland
A. Frenulum
_____ 22. Lining the small intestine
B. Large intestine
_____ 23. Muscularis
C. Throat
_____ 24. Tongue
D. Mesentery
_____ 25. Large intestine
E. Appendix
_____ 26. Vitamin K
F. Esophagus
_____ 27. Foodpipe
G. Villi
_____ 28. Pharynx
H. Peristalsis
_____ 29. Small structure attached to cecum
I.
Colon
_____ 30. Peritoneum
J.
Parotid
Copyright © 2012 by Elsevier Inc. All rights reserved.
Structure & Function of the Body, 14th ed.
Thibodeau & Patton
_________________________________________________________ Chapter 15  The Digestive System
647
Identification
Identify the numbered structures and write your answers in the corresponding blanks.
31. Gallbladder and Bile Ducts
(1) _____________________________________
(7) ______________________________________
(2) _____________________________________
(8) ______________________________________
(3) _____________________________________
(9) ______________________________________
(4) _____________________________________
(10) ______________________________________
(5) _____________________________________
(11) ______________________________________
(6) _____________________________________
(12) ______________________________________
Copyright © 2012 by Elsevier Inc. All rights reserved.
Structure & Function of the Body, 14th ed.
Thibodeau & Patton
648 Chapter 15  The Digestive System _________________________________________________________
32. Stomach
(1) _____________________________________
(8) ______________________________________
(2) _____________________________________
(9) ______________________________________
(3) _____________________________________
(10) ______________________________________
(4) _____________________________________
(11) ______________________________________
(5) _____________________________________
(12) ______________________________________
(6) _____________________________________
(13) ______________________________________
(7) _____________________________________
Copyright © 2012 by Elsevier Inc. All rights reserved.
Structure & Function of the Body, 14th ed.
Thibodeau & Patton
_________________________________________________________ Chapter 15  The Digestive System
649
ANSWERS TO CHAPTER 15 STUDENT ASSIGNMENT
Multiple Choice
Matching
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
B
C
A
D
A
B
B
C
C
A
J
G
H
A
I
B
F
C
E
D
Completion
Identification
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
31. Gallbladder and bile ducts: (1) right and left
hepatic ducts; (2) common hepatic duct; (3)
common bile duct; (4) accessory duct; (5)
pancreas; (6) pancreatic duct; (7)
duodenum; (8) major duodenal papilla; (9)
sphincter muscles; (10) minor duodenal
papilla; (11) gallbladder; (12) cystic duct
32. Stomach: (1) fundus; (2) body; (3) greater
curvature; (4) rugae; (5) pylorus; (6) pyloric
sphincter; (7) duodenum; (8) lesser
curvature; (9) oblique muscle layer; (10)
circular muscle layer; (11) longitudinal
muscle; (12) cardiac sphincter; (13)
esophagus
N
J
P
Q, R, A
W
H, K, D
E
T, U, C, X
G
I, O, S, F
Copyright © 2012 by Elsevier Inc. All rights reserved.
Structure & Function of the Body, 14th ed.
Thibodeau & Patton