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CHAPTER
33
The Digestive
System
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33-2
Learning Outcomes (cont.)
33.1 Describe the organs of the alimentary
canal and their functions.
33.2 Explain the functions of the digestive
system’s accessory organs.
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33-3
Learning Outcomes (cont.)
33.3 Identify the nutrients absorbed by the
digestive system and where they are
absorbed.
33.4 Describe the causes, signs and
symptoms, and treatments of various
common diseases and disorders of the
digestive system.
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33-4
Introduction
• Digestion – mechanical and
chemical breakdown of
foods
• Organs of digestion
– Alimentary canal organs
form a pathway extending
from the mouth to the anus
– Accessory organs
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33-5
Characteristics of the Alimentary Canal
• Mucosa
– Epithelial tissue
– Secretes enzymes and mucus
– Absorbs nutrients
• Submucosa – loose connective tissue,
blood vessels, glands, and nerves
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33-6
Characteristics of the Alimentary Canal
• Muscular layer
– Smooth muscle
– Contracts to move materials through the canal
• Serosa or peritoneum
– Visceral peritoneum
– Parietal peritoneum
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33-7
Characteristics of the Alimentary Canal
(cont.)
•
Movements
– Churning ~ mixes substances
– Peristalsis ~ moves substances
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33-8
The Mouth
• Buccal cavity
• Mechanical digestion
• Starts chemical digestion
• Cheeks – hold food in mouth
• Lips – judge temperature of food
The Mouth
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33-9
The Mouth (cont.)
• Tongue
• Palate
– Mixes and holds food
between teeth
– Contains taste buds
– Lingual frenulum
– Lingual tonsils
– Hard palate
– Soft palate
– Uvula
• Lymphatic tissue
– Palatine tonsils
– Pharyngeal tonsils or
adenoids
The Mouth
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33-11
The Mouth (cont.)
• Salivary glands
– Cells
• Serous – watery fluid
and amylase
• Mucous
– Parotid gland
– Submandibular gland
– Sublingual gland
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33-12
The Mouth (cont.)
• Teeth – decrease size
of food particles
– Incisors
– Cuspids or canines
– Bicuspids and molars
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33-13
Pharynx
• Functions
• Divisions
– Connects nasal
cavity with oral
cavity for breathing
– Nasopharynx
– Oropharynx
– Laryngopharynx
– Pushes food into
esophagus
Pharynx
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33-14
Pharynx (cont.)
Swallowing
1. Soft palate rises; uvula covers opening
between nasal and oral cavity
2. Epiglottis covers larynx – keeps food out
3. Tongue presses against roof of mouth,
forcing food into oropharynx
Pharynx
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33-15
Pharynx (cont.)
Swallowing
4. Muscles in pharynx contract – forcing food
toward esophagus
5. Esophagus opens
6. Muscles of pharynx push food through
cardiac sphincter
Pharynx
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33-17
The Esophagus
• Connects pharynx to stomach
• Esophageal hiatus
• Cardiac sphincter
– Circular band of muscle
– Controls movement of food into stomach
Upper
Esophagus
Lower
Esophagus
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33-18
The Stomach
• Rugae – folds of the
inner lining
• Absorbs
– Alcohol
– Water
– Some fat-soluble drugs
• Functions
– Receives food
– Mixes bolus with gastric juices  chyme
– Starts protein digestion
– Moves food into small intestine
Stomach
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33-19
The Stomach
• Sections
– Cardiac region
– Body
– Fundus
– Pylorus
• Pyloric sphincter – controls movement
into the small intestine
Stomach
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33-20
The Stomach
• Lining – gastric glands
– Cells ~ mucous, chief, and parietal
– Stimulated by
• Parasympathetic nervous system
• Gastrin – made by the stomach
– Inhibited by cholecystokinin (CCK) made by
the small intestine
Stomach
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33-22
The Small Intestine
• Functions
• Sections
– Digestion
– Duodenum
– Absorption of
nutrients
– Jejunum
– Ileum
• Mesentery
Small
Intestine
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33-23
The Small Intestine (cont.)
• Microvilli
• Intestinal glands
– Mucus and water
– Enzymes
• Peptidases
• Sucrase, maltase,
and lactase
• Intestinal lipase
– Stimulated by
• Parasympathetic
nervous system
• Stretching of the
intestinal wall
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33-24
The Small Intestine (cont.)
• Absorbs most nutrients
• Wall contracts to mix and propel chyme
• Ileocecal sphincter – controls movement of
chyme into cecum of the large intestine
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33-26
The Large Intestine
• Cecum
• Transverse colon
• Vermiform
• Descending colon
appendix
• Sigmoid colon
• Ascending colon
Large
Intestine
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33-27
The Rectum and Anal Canal
• Rectum – off
sigmoid colon
• Feces – left-over
chyme
• Anal canal
• Defecation reflex
– End of rectum
– Anus
– Stimulated by mass
movements
– Relaxation of anal
sphincters
Rectum &
Anal Canal
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33-29
Apply Your Knowledge
1. Matching:
ANSWER:
B Buccal cavity
___
A. Saliva
D Roof of mouth
___
B. Mouth
E Grind food
___
C. Bolus
F Adenoids
___
D. Palate
A Water, enzymes, and mucus
___
E. Bicuspids
___
B Mass of food mixed with saliva and mucus
F. Pharyngeal
gland
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33-30
Apply Your Knowledge
2. What are the functions of the stomach?
ANSWER: The stomach’s functions are to receive
the bolus of food, mix it with gastric juice, start
protein digestion, and move food into the small
intestine. It also absorbs alcohol, water, and some
drugs.
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33-31
Apply Your Knowledge
3. Matching:
Super!
ANSWER:
___
G Vermiform appendix
A. Feces
___
F Crosses the abdomen
B. Ascending colon
___
B Up right side of abdomen
C. Anal canal
___
E S-shaped tube
D. Defecation reflex
___
H Down left side of abdomen
E. Sigmoid
___
A Leftover chyme
F. Transverse colon
___
C Last section of rectum
G. Cecum
___
D Allows anal sphincters to relax
H. Descending colon
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33-32
Characteristics of the Digestive Accessory
Organs
• The Liver
– Hepatic lobules
• Smaller divisions of
lobes
– Part of liver’s function
~ store vitamins and
iron
• Macrophages
• Hepatocytes – bile
– Hepatic portal vein
To Liver
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33-33
The Liver (cont.)
• Hepatic duct
– Bile from liver
– Merges with cystic duct and forms common
bile duct
• Common bile duct ~ delivers bile to
duodenum
To Liver
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33-34
The Gallbladder
• Only function is to store bile
– Cholecystokinin stimulates gallbladder to
release bile
– Bile salts
• Break up large fat globules
• Increase absorption of fatty acids, cholesterol, and
fat-soluble vitamins
To Gallbladder
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33-36
The Pancreas
• Acinar cells produce pancreatic juice
– Pancreatic amylase
– Pancreatic lipase
– Nucleases
– Trypsin, chymotrypsin, and carboxypeptidase
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33-37
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33-38
The Pancreas (cont.)
• Releases bicarbonate ions into duodenum
• Stimulated to release enzymes by
– Parasympathetic nervous system
– Secretin and cholecystokinin
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33-39
Apply Your Knowledge
1. What is the route of bile through the liver and
gallbladder?
ANSWER: Bile is made in the hepatocytes and leaves the liver
through the hepatic duct. The hepatic duct merges with the
cystic duct from the gallbladder to form the common bile
duct, which delivers bile to the duodenum.
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33-40
Apply Your Knowledge
2. What are the pancreatic enzymes and what do
they do?
ANSWER: They are:
Pancreatic amylase – digests carbohydrates
Pancreatic lipase – digests lipids
Nucleases – digest nucleic acids
Trypsin, chymotrypsin, and carboxypeptidase – digest proteins
Good Job!
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33-41
The Absorption of Nutrients
• Nutrients – necessary food substances
– Carbohydrates
– Proteins
– Lipids
– Vitamins
– Minerals
– Water
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33-42
The Absorption of Nutrients (cont.)
• Carbohydrates
– Starches ~ polysaccharides
– Simple sugars
• Monosaccharides and disaccharides
• Excess glucose stored as glycogen
– Cellulose – provides fiber or bulk
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33-43
The Absorption of Nutrients (cont.)
• Lipids
– Used to make energy when glucose levels are
low
– Triglycerides
• Most abundant
• Excess stored in adipose tissue
– Cholesterol – essential for cell growth and
function
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33-44
The Absorption of Nutrients (cont.)
• Protein
• Vitamins
– Fat-soluble
– Water-soluble
– Requirements vary
– Used for growth and
tissue repair
• Minerals
– Found in bones and teeth
– Used to make enzymes, cell membranes, and
proteins
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33-45
Apply Your Knowledge
True or False:
ANSWER:
___
T Carbohydrates are starches, simple sugars, and cellulose.
liver
___
F Excess glucose is stored in the gallbladder as glycogen.
most
___
F Triglycerides are the least abundant lipids
___
T Linoleic acid is an essential fatty acid.
fat-soluble
___
F A, D, E and K are water-soluble vitamins.
___
T Minerals are used by cells to make enzymes.
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33-46
Aging and the Digestive System
• Decreased
– Motility
– Absorption
– Ability to detoxify
blood
• More likely to
develop ulcers and
cancers
• Sense of taste
altered
• Dietary changes
due to
– Isolation
– Depression
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33-47
Common Diseases and Disorders
Disease/Disorder Description
Appendicitis
Inflammation of the appendix;
can be life-threatening if not
treated promptly
Cirrhosis
Chronic liver disease; normal
tissue is replaced with
nonfunctional scar tissue
Cholelithiasis (gall Hard deposits of cholesterol or
stones)
bilirubin in the gall bladder
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33-48
Common Diseases and Disorders
Disease/Disorder Description
Colitis
Inflammation of the large
intestine; can be acute or
chronic
Colorectal cancer Arises from lining of rectum or
colon; curable if treated early
Constipation
Difficult defecation
Crohn’s disease
Inflammatory bowel disease;
typically effects small intestine
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33-49
Common Diseases and Disorders (cont.)
Disease/Disorder Description
Diarrhea
Watery and frequent feces;
usually self-limiting
Diverticulitis
Inflammation of diverticula
Diverticulosis – diverticula with
no inflammation
Inflammation of the stomach
lining; “upset stomach”
Gastritis
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33-50
Common Diseases and Disorders (cont.)
Disease/Disorder Description
Heartburn
Hemorrhoids
Hepatitis
Hiatal hernia
Gastroesophageal reflux
disease (GERD); stomach
acids push into esophagus
Varicose veins of rectum or anus
Inflammation of the liver; various
types
Portion of stomach protrudes
into the chest through an
opening in the diaphragm
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33-51
Common Diseases and Disorders (cont.)
Disease/Disorder Description
Inguinal hernia
Portion of large intestine
protrudes in the inguinal canal
(where thigh and trunk meet) or,
in males, into the scrotum
Oral cancer
Usually involves the lips or
tongue but can occur anywhere
in the mouth; tends to spread
rapidly
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33-52
Common Diseases and Disorders (cont.)
Disease/Disorder Description
Pancreatic cancer Fourth leading cause of cancer
deaths in the U.S.
Stomach cancer
Commonly in cardiac portion of
the stomach; occurs more
frequently in Japan, Chili, and
Iceland
Stomach ulcers
Breakdown in lining of the
stomach
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33-53
Apply Your Knowledge
Matching:
ANSWER:
___
E Inflammation of the large intestine
A. Heartburn
___
D Inflammatory bowel disease
B. Hemorrhoids
___
F Watery and frequent feces
C Difficult defecation
___
C. Constipation
___
G Inflammation of the stomach lining
E. Colitis
D. Crohn’s disease
H Inflammation of pouches in the intestinal wall F. Diarrhea
___
___
A GERD
G. Gastritis
B Varicose veins of rectum
___
H. Diverticulitis
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33-54
In Summary
33.1 The pathway of food through the
alimentary canal starts with the mouth
and continues through the pharynx,
esophagus, stomach, small intestine,
large intestine, and anal canal.
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33-55
In Summary (cont.)
33.2 The accessory organs to the digestive
system include the liver, gallbladder,
and pancreas.
33.3 Nutrients absorbed by the body include
carbohydrates, proteins, lipids,
vitamins, minerals, and water. Most of
the absorption takes place in the small
intestine.
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33-56
In Summary (cont.)
33.4 There are many common diseases and
disorders of the digestive system with
varied signs, symptoms, and
treatments.
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33-57
End of Chapter 33
Take all that is given
whether wealth, love or
language; nothing comes
by mistake and with good
digestion all can be turned
to health.
~ George Herbert
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in any manner. This document may not be copied, scanned, duplicated, forwarded, distributed, or posted on a website, in whole or part.