Download The Digestive System - McGraw Hill Higher Education

CHAPTER
29
The Digestive
System
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29-2
Learning Outcomes
29.1 List the functions of the digestive system.
29.2 Trace the pathway of food through the
alimentary canal.
29.3 Describe the structure and functions of the
mouth, teeth, tongue, and salivary glands.
29.4 Describe the structure and function of the
pharynx.
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29-3
Learning Outcomes (cont.)
29.5 Describe the swallowing process.
29.6 Describe the structure of the esophagus and
tell how it propels food into the stomach.
29.7 Describe the structure and functions of the
stomach.
29.8 List the substances secreted by the stomach
and give their functions.
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29-4
Learning Outcomes (cont.)
29.9 Describe the structure and functions of the
small intestine.
29.10 List the substances secreted by the small
intestine and describe the importance of
each.
29.11 Describe the structure and functions of the
large intestine, including the anal canal and
rectum.
29.12 Explain the structures and functions of the
liver, gallbladder, and pancreas.
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29-5
Learning Outcomes (cont.)
29.13 List the substances released by the liver,
gallbladder, and pancreas into the small
intestine and give the function of each
secretion.
29.14 Tell what types of nutrients are absorbed by
the digestive system and where they are
absorbed.
29.15 Describe the causes, signs and symptoms,
and treatments of various diseases and
disorders of the digestive system.
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29-6
Introduction
• Digestion
– Mechanical and chemical
breakdown of foods into forms
that body cells can absorb
– The organs of the digestive
system carry out digestion
• Two categories
– Alimentary canal organs
– Accessory organs
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29-7
Alimentary Canal
•
Wall of alimentary canal
– Mucosa
•
•
•
Innermost layer; epithelial tissue
Secretes enzymes and mucus into lumen
Absorbs nutrients
– Submucosa
•
•
Inferior to mucosa; loose connective tissue, blood
vessels, glands, and nerves
Blood vessels carry away absorbed nutrients
– Muscular layer
•
•
Just outside submucosa; layers of smooth muscle
Contracts to move materials through the canal
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29-8
Alimentary Canal (cont.)
– Serosa
•
Double-walled outermost layer: peritoneum
– Visceral peritoneum
» Innermost wall of serosa
» Secretes serous fluid to keep outside of canal moist
– Parietal peritoneum
» Abdominal lining
•
Movements
– Churning – mixes substances in the canal
– Peristalsis – propels substances through the
tract
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29-9
Apply Your Knowledge
What are the layers of the wall of the alimentary canal and
what do they do?
ANSWER: The layers are:
Mucosa: innermost layer; secretes enzymes and mucus into the canal and
absorbs nutrients
Submucosa: inferior to the mucosa; carries away absorbed nutrients
Muscular layer: just outside the submucosa; contracts to move materials
through the canal
Serosa: double-walled outer layer; secretes serous fluid to keep outside of
canal moist
Bravo!
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29-10
The Mouth
• Buccal cavity
• Mechanical digestion
– Takes in food and
reduces its size by
chewing
• Starts chemical
digestion
– Saliva contains the
enzyme amylase, which
breaks down
carbohydrates
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29-11
The Mouth (cont.)
• Cheeks hold food in mouth
• Lips – sensory nerve fibers that judge
temperature of food
• Tongue
– Skeletal muscles covered by mucous membrane
– Lingual frenulum – holds tongue to floor of mouth
– Mixes food, holds food between teeth, contains taste
buds
– Lingual tonsils – lymphatic tissue destroys bacteria
and viruses on back of tongue
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29-12
The Mouth (cont.)
• Palate
– Roof of mouth
– Separates oral cavity from nasal cavity
– Uvula – portion of soft palate that hangs
down in throat
• Lymph tissue
– Palatine tonsils (oropharynx)
– Pharyngeal tonsils – adenoids
(nasopharynx)
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29-13
The Mouth (cont.)
• Teeth – decrease
size of food
particles
– Incisors – bite off
food pieces
– Cuspids – tear
tough food
– Bicuspids and
molars – grind
food
• Salivary glands
– Cells
• Serous
• Mucous
– Glands
• Parotid
• Submandibular
• Sublingual
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29-14
Apply Your Knowledge
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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29-15
Pharynx
• Throat
• Functions
– Connects nasal
cavity with oral
cavity for breathing
– Pushes food into
esophagus
• Divisions
– Nasopharynx
• Behind nasal cavity
– Oropharynx
• Behind oral cavity
– Laryngopharynx
• Behind larynx
• Continues as
esophagus
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29-16
Pharynx (cont.)
•
Swallowing –
automatic process
1.
Soft palate rises, uvula
covers opening
between nasal and oral
cavity
2.
Epiglottis covers larynx,
keeping food out of it
3.
Tongue presses
against roof of mouth,
forcing food into
oropharynx
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29-17
Pharynx (cont.)
 Muscles in pharynx contract,
moving food toward
esophagus
 Esophagus opens
 Food is pushed into
esophagus by muscles of
pharynx
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29-18
The Esophagus
• Muscular tube connecting pharynx to
stomach
– Esophageal hiatus – hole in diaphragm
through which esophagus passes
• Cardiac sphincter
– Circular band of muscle at the opening of the
stomach
– controls movement of food into stomach
© 2011 The McGraw-Hill Companies, Inc. All rights reserved.
29-19
Apply Your Knowledge
Matching:
ANSWER:
___
E Connects nasal cavity with oral cavity
A. Cardiac sphincter
D Covers the opening of larynx
___
B. Esophageal hiatus
___
B Hole in diaphragm
C. Sphincter
A Controls movement of food into stomach
___
D. Epiglottis
___
C Circular bands of muscle
E. Pharynx
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29-20
The Stomach
• Below the diaphragm
in the upper left
quadrant of the
abdominal cavity
• Functions
– Receive food from
esophagus
– Mix bolus with gastric
juice
– Start protein digestion
– Move food into small
intestine
• Sections
–
–
–
–
Cardiac region
Fundus
Body
Pylorus
• Pyloric sphincter
– Controls movement of
substances into small
intestine
Stomach
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29-21
The Stomach (cont.)
• Lining of stomach
– Rugae – folds of the inner lining
– Gastric glands
• Mucous cells – secrete mucus to protect the lining
• Chief cells – secrete pepsinogen  pepsin,
which digests protein
• Parietal cells
– Hydrochloric acid needed to convert pepsinogen to
pepsin
– Intrinsic factor needed for vitamin B12 absorption
Stomach
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29-23
The Stomach (cont.)
• Gastric glands stimulated by
– Parasympathetic nervous system
– Gastrin (hormone)
• Cholesystokinin (hormone) secreted by the
small intestine inhibits gastric glands
• Stomach absorbs alcohol, water, and some fatsoluble drugs
• Chyme – mixture of food and gastric juices
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29-24
Apply Your Knowledge
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.
Right Answer!
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29-25
The Small Intestine
• Tubular organ
extending from the
stomach to the large
intestine
• Functions
– Digestion
– Absorption of nutrients
• Duodenum
– C-shaped
– Short
• Jejunum
– Coiled
– Majority of small
intestine
Small
Intestine
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29-26
The Small Intestine (cont.)
• Ileum – attached to large intestine
• Mesentery
– Fan-like tissue that holds jejunum and ileum
in the abdominal cavity
– Attaches to the posterior wall of the abdomen
• Ileocecal sphincter
– Controls movement of chyme from the ileum
to the cecum of the large intestine
Small
Intestine
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29-27
The Small Intestine (cont.)
• Lining of small intestine
– Microvilli – increase surface area
– Intestinal glands
• Mucus and water
• Enzymes
– Peptidases – digest proteins
– Sucrase, maltase, and lactase – digest sugars
– Intestinal lipase – digests fats
• Primary controls
– Parasympathetic nervous system
– Stretching of intestinal wall
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29-29
Apply Your Knowledge
Your patient states that she is lactose
intolerant. What does that mean?
ANSWER: She cannot produce lactase and cannot
digest lactose, which is the sugar in dairy products.
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29-30
The Large Intestine
• Extends from the ileum to the anus
• Cecum
– Beginning of large intestine
– Veriform appendix
• Ascending colon
– Portion that goes up the right side of the
abdominal cavity
Large
Intestine
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29-31
The Large Intestine (cont.)
• Transverse colon – crosses abdominal
cavity from right to left
• Descending colon – down left side of
abdominal cavity
• Sigmoid colon – S-shaped portion in
pelvic cavity
• Absorbs water and electrolytes
Large
Intestine
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29-32
The Rectum and Anal Canal
• Rectum – off sigmoid colon
• Anal canal
– Last few centimeters of rectum
– Opening to outside of body is the anus
Large
Intestine
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29-33
The Rectum and Anal Canal (cont.)
• Feces
– Leftover chyme
– Consists of undigested solid materials,
little water, ions, mucus, cells of
intestinal lining, and bacteria
• Defecation reflex
– Triggered by periodic contractions of
large intestine
– Allows anal sphincters to relax
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29-35
Apply Your Knowledge
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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29-36
The Liver
• Lobular organ in right upper quadrant
– Large right lobe and smaller left lobe
• Hepatic lobules – contain macrophages
• Hepatocytes – process nutrients in blood and
make bile
• Part of liver’s function
– Store vitamins and iron
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29-37
The Liver (cont.)
• Hepatic portal vein –
carries blood from
digestive organs to
hepatic lobules
• Hepatic duct – bile from
liver
• Hepatic duct merges with
cystic duct from
gallbladder and forms
common bile duct
• Common bile duct –
delivers bile to duodenum
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29-38
The Gallbladder
• Small sac-like structure
located beneath the liver
• Only function is to store
bile
• Cholecystokinin causes
the gallbladder to
release bile
Gallbladder
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29-39
Apply Your Knowledge
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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29-40
The Pancreas
Located behind the stomach
 Acinar cells produce pancreatic juice, which contains
these enzymes:


Pancreatic amylase –
digests carbohydrates

Pancreatic lipase –
digests lipids

Nucleases – digest
nucleic acids

Trypsin, chymotrypsin,
and carboxypeptidase –
digest proteins
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29-41
The Pancreas (cont.)

Also secretes bicarbonate ions into
duodenum


Neutralize acidic chyme
Enzyme release stimulated by


Parasympathetic nervous system
Hormones secretin and cholecystokinin
(from small intestine)
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29-42
Apply Your Knowledge
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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29-43
The Absorption of Nutrients
• Nutrients are necessary food
substances
– Carbohydrates
– Proteins
– Lipids
– Vitamins
– Minerals
– Water
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29-44
The Absorption of Nutrients (cont.)
• Carbohydrates – provide energy
– Polysaccharides – starches
– Monosaccharides and disaccharides –
simple sugars
– Cellulose – provides fiber or bulk
• Lipids – used for energy when glucose
levels are low
– Triglycerides
– Cholesterol – essential for cell growth and
function
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29-45
The Absorption of Nutrients (cont.)
• Protein – used for growth and repair of tissue
– Essential amino acids body cannot make
• Vitamins
– Fat-soluble
– Water-soluble
• Minerals – used to make enzymes, cell
membranes, and proteins
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29-46
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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29-47
Aging and the Digestive System
• Decreased motility –
GERD
• Decreased ability to
detoxify blood
• Decreased absorption
• Sense of taste altered
• More likely to develop
ulcers and cancers
• Dietary changes due
to
– Isolation
– Depression
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29-48
Common Diseases and Disorders
Disease/Disorder
Description
Appendicitis
Inflammation of the appendix; can be lifethreatening if not treated promptly
Cirrhosis
Chronic liver disease; normal tissue is replaced
with nonfunctional scar tissue
Colitis
Inflammation of the large intestine; can be acute or
chronic
Colorectal cancer
Arises from lining of rectum or colon; curable if
treated early
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29-49
Common Diseases and Disorders (cont.)
Disease/Disorder
Description
Constipation
Difficult defecation
Crohn’s disease
Inflammatory bowel disease; typically effects
small intestine
Diarrhea
Watery and frequent feces; usually self-limiting
Diverticulosis
Abnormal pouches in the intestinal wall; no
inflammation present
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29-50
Common Diseases and Disorders (cont.)
Disease/Disorder
Description
Diverticulitis
Inflammation of diverticuli (abnormal pouches in
intestinal wall) of the intestine
Gastritis
Inflammation of the stomach lining; “upset
stomach”
Heartburn
Gastroesophageal reflux disease (GERD);
stomach acids push into esophagus
Hemorrhoids
Varicose veins of rectum or anus
Hepatitis
Inflammation of the liver; various types
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29-51
Common Diseases and Disorders (cont.)
Disease/Disorder
Description
Hiatal hernia
Portion of stomach protrudes into the chest
through an opening (usually the esophageal
hiatus) in the diaphragm
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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29-52
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; can be
caused by bacteria (H. pylori) or smoking, alcohol,
excessive aspirin use, and hypersecretion of
stomach acid
© 2011 The McGraw-Hill Companies, Inc. All rights reserved.
29-53
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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29-54
In Summary
29.1 The digestive system uses mechanical and chemical
mechanisms to break down food into forms that the
body’s cells can use.
29.2 The pathway of food through the alimentary canal
starts with the mouth through the pharynx,
esophagus, stomach, small intestines, large
intestines, and anal canal.
29.3 The mouth takes in food and the teeth assist in
reducing its size through chewing. The tongue mixes
food and holds it between the teeth. The salivary
glands produce saliva to assist in moistening and
breaking down food.
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29-55
In Summary (cont.)
29.4 The pharynx is a long muscular tube extending from
behind the nose to the esophagus, connecting the
oral and nasal cavities. It also acts to push food into
the esophagus.
29.5 The soft palate rises, closing the opening between the
nasal and oral cavities. The epiglottis covers the
laryngeal opening. Food is forced into the oropharynx
by the tongue, and the pharynx contracts, pushing
food to the esophagus.
29.6 The esophagus is a muscular tube that pushes food
toward the stomach through muscular contractions. At
the end of the esophagus is the cardiac sphincter, the
entrance to the stomach.
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29-56
In Summary (cont.)
29.7 The stomach is in the LUQ. It receives food, mixes it
with gastric juices, starting protein digestion, and
moves food into the small intestine. The stomach has
four regions: cardiac region, fundus, body, and
pylorus.
29.8 The stomach’s gastric glands include mucous cells
that secret mucus, chief cells that secret pepsinogen,
and parietal cells that secrete hydrochloric acid and
intrinsic factor.
29.9 The small intestine carries out most of the nutrient
absorption. The sections of the small intestine are, in
order, duodenum, jejunum, and ileum.
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29-57
In Summary (cont.)
29.10 The small intestine secretes peptidases to digest
protein; sucrase, maltase and lactase, which digest
sugars; and intestinal lipase, which digests fats.
29.11 The components of the large intestine are the cecum
with its vermiform appendix, ascending colon,
transverse colon, descending colon, sigmoid colon,
rectum, and anal canal ending in the anus. The large
intestine’s primary job is to rid the body of solid waste
by defecation.
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29-58
In Summary (cont.)
29.12 The liver is in the RUQ. It stores vitamins and iron
and produces macrophages to fight infection. The
gallbladder stores the bile produced by the liver. The
pancreas produces pancreatic juices that assist in
carbohydrate, lipid, and protein digestion.
29.13 The liver secretes bile for fat digestion. Bile is
released by the gallbladder for fat digestion.
Pancreatic juices contain pancreatic amylase for
carbohydrate digestion; lipase for lipid digestion;
nucleases to digest nucleic acids; and trypsin,
chymotrypsin, and carboxypeptidase to digest
proteins.
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29-59
In Summary (cont.)
29.14 Nutrients absorbed by the body include
carbohydrates, proteins, lipids, vitamins, minerals,
and water. Most of the absorption takes place in the
small intestine.
29.15 Common diseases and disorders of the digestive
system include inflammatory disorders such as
appendicitis and colitis; cancers including colorectal,
oral, and pancreatic cancers; as well as common
symptoms such as diarrhea, constipation, and
GERD. For more detailed information regarding these
and other common disorders, please see the
Pathophysiology section at the end of this chapter.
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29-60
End of Chapter 29
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
© 2011 The McGraw-Hill Companies, Inc. All rights reserved.