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CHAPTER 23 (8th edition)
THE DIGESTIVE SYSTEM part 1
Copyright © 2011 Pearson Education, Inc.
2. Digestive System
•
Two groups of organs
1. Alimentary canal (gastrointestinal or GI tract)
•
Digests and absorbs food
•
Mouth, pharynx, esophagus, stomach,
small intestine, and large intestine
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3. Digestive System
2. Accessory digestive organs
•
Teeth, tongue, gallbladder
•
Digestive glands
•
Salivary glands
•
Liver
•
Gall bladder
•
pancreas
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4
Fig. 23.1
Pg 852
Mouth (oral cavity)
Tongue
Esophagus
Liver
Gallbladder
Duodenum
Jejunum
Small
intestine Ileum
Anus
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Parotid gland
Sublingual gland Salivary
Submandibular
glands
gland
Pharynx
Stomach
Pancreas
(Spleen)
Transverse colon
Descending colon
Ascending colon
Large
Cecum
intestine
Sigmoid colon
Rectum
Vermiform appendix
Anal canal
Figure 22.1
5. Digestive Processes
•
Six essential activities
1. Ingestion
2. Propulsion
3. Mechanical digestion
4. Chemical digestion
5. Absorption
6. Defecation
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6 Fig. 23.
Pg. 853
Ingestion
Mechanical
digestion
• Chewing (mouth)
• Churning (stomach)
• Segmentation
(small intestine)
Chemical
digestion
Food
Pharynx
Esophagus
Propulsion
• Swallowing
(oropharynx)
• Peristalsis
Stomach (esophagus,
stomach,
small intestine,
large intestine)
Absorption
Lymph
vessel
Small
intestine
Large
intestine
Defecation
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Blood
vessel
Mainly H2O
Feces
Anus
Figure 22.2
7 Fig. 23.5a; page 855
From
mouth
(a) Peristalsis: Adjacent segments of
alimentary tract organs alternately contract
and relax, which moves food along the tract
distally.
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(b) Segmentation: Nonadjacent segments
of alimentary tract organs alternately
contract and relax, moving the food
forward then backward. Food mixing and
slow food propulsion occurs.
Figure 22.3
8. GI tract regulatory mechanisms
2. Intrinsic and extrinsic controls
•
Enteric nerve plexuses (gut brain) initiate
short reflexes in response to stimuli in the GI
tract
•
Long reflexes in response to stimuli inside or
outside the GI tract involve CNS centers and
autonomic nerves
•
Hormones from cells in the stomach and
small intestine stimulate target cells in the
same or different organs
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9. Peritoneum and Peritoneal Cavity
• Peritoneum: serous membrane of the
abdominal cavity
• Visceral peritoneum on external surface of
most digestive organs
• Parietal peritoneum lines the body wall
• Peritoneal cavity
• Between the two peritoneums
• Fluid lubricates mobile organs
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Abdominopelvic
cavity
Vertebra
Dorsal
mesentery
Parietal
peritoneum
Ventral
mesentery
Visceral
peritoneum
Peritoneal
cavity
Alimentary
canal organ
Liver
(a) Schematic cross sections of abdominal cavity
illustrate the peritoneums and mesenteries.
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Figure 22.5a
11. Peritoneum and Peritoneal Cavity
• Mesentery is a double layer of peritoneum
• Routes for blood vessels, lymphatics, and
nerves
• Holds organs in place and stores fat
• Retroperitoneal organs lie posterior to the
peritoneum
• Intraperitoneal (peritoneal) organs are
surrounded by the peritoneum
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12
Fig. 23.5b; page 855
Abdominopelvic
cavity
Mesentery
resorbed
and lost
Alimentary
Alimentary canal organ in
canal organ
a retroperitoneal position
(b) Some organs lose their mesentery and
become retroperitoneal during development.
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Figure 22.5b
13. Blood Supply: Splanchnic Circulation
• Arteries- that branch off the aorta and go to
the digestive system and the hepatic portal
system
• Hepatic, splenic, and left gastric
• Inferior and superior mesenteric
• Hepatic portal circulation
• Drains nutrient-rich blood from digestive
organs
• Delivers it to the liver for processing
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14. Histology of the Alimentary Canal
• Four basic layers (tunics)
• 1. Mucosa
• 2. Submucosa
• 3. Muscularis externa
• 4. Serosa
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15 Fig. 23.6; page 857
Nerve
Artery
Vein
Mesentery
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Intrinsic nerve plexuses
• Myenteric nerve plexus
• Submucosal nerve plexus
Glands in submucosa
Mucosa
• Epithelium
• Lamina propria
• Muscularis
mucosae
Submucosa
Muscularis
externa
• Longitudinal
muscle
• Circular muscle
Serosa
• Epithelium
• Connective
tissue
Lumen
Gland in mucosa
Lymphatic
Mucosa-associated
Duct of gland outside
vessel
lymphoid tissue
alimentary canal
Figure 22.6
16.
1. Mucosa
• Lines the lumen
• Functions
• Secretes mucus, digestive enzymes and
hormones
• Absorbs end products of digestion
• Protects against infectious disease
• Three sublayers: A. epithelium, B. lamina
propria, and C. muscularis mucosae
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17.
Mucosa
• A. Epithelium
• Simple columnar epithelium and mucussecreting cells
• Mucus
• Protects digestive organs from enzymes
• Eases food passage
• May secrete enzymes and hormones (e.g., in
stomach and small intestine)
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18. Mucosa
• B. Lamina propria
???
• Loose areolar connective tissue
• Capillaries for nourishment and absorption
• Lymphoid follicles (part of MALT)
• C. Muscularis mucosae: smooth muscle that
produces local movements of mucosa ???
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19.
2. Submucosa
• Submucosa
• Dense connective tissue
???
• Blood and lymphatic vessels, lymphoid
follicles, and submucosal nerve plexus ???
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20.
3. Muscularis Externa
• Responsible for segmentation and peristalsis
• Inner circular and outer longitudinal layers
• Myenteric nerve plexus ???
• Sphincters in some regions
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21.
4. Serosa
• Visceral peritoneum
• Replaced by the fibrous adventitia in the
esophagus skip
• Retroperitoneal organs have both an adventitia
and serosa skip
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22 Fig. 23.6 page 857
Nerve
Artery
Vein
Mesentery
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Intrinsic nerve plexuses
• Myenteric nerve plexus
• Submucosal nerve plexus
Glands in submucosa
Mucosa
• Epithelium
• Lamina propria
• Muscularis
mucosae
Submucosa
Muscularis
externa
• Longitudinal
muscle
• Circular muscle
Serosa
• Epithelium
• Connective
tissue
Lumen
Gland in mucosa
Lymphatic
Mucosa-associated
Duct of gland outside
vessel
lymphoid tissue
alimentary canal
Figure 22.6
23.
Enteric Nervous System
• Intrinsic nerve supply of the alimentary canal
•
Skip below
• Submucosal nerve plexus
• Regulates glands and smooth muscle in the
mucosa
• Myenteric nerve plexus
• Controls GI tract motility
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24.
Enteric Nervous System
• Linked to the CNS via afferent visceral fibers
•
skip below
• Long ANS fibers synapse with enteric
plexuses
• Sympathetic impulses inhibit secretion and
motility
• Parasympathetic impulses stimulate
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25. Mouth
• Oral (buccal) cavity
• Bounded by lips, cheeks, palate, and tongue
• Oral orifice is the anterior opening
• Lined with stratified squamous epithelium
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Soft palate
Palatoglossal arch
Hard palate
Oral cavity
Palatine tonsil
Tongue
Oropharynx
Lingual tonsil
Epiglottis
Hyoid bone
Laryngopharynx
26
Uvula
Fig. 23.7a
Page 857
Palantine bone
Palantine
process of
maxillla
Esophagus
Trachea
(a) Sagittal section of the oral cavity and pharynx
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Figure 22.7a
27. Lips and Cheeks
• Contain orbicularis oris and buccinator
muscles
• Vestibule: recess internal to lips and cheeks,
external to teeth and gums
• Oral cavity proper lies within the teeth and
gums
• Labial frenulum: median attachment of each
lip to the gum
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28 Fig. 23.7b; page 859
Gingivae (gums)
Palatine raphe
Hard palate
Soft palate
Uvula
Palatine tonsil
Sublingual fold
with openings of
sublingual ducts
Vestibule
Lower lip
Upper lip
Superior labial
frenulum
Palatoglossal arch
Palatopharyngeal
arch
Posterior wall
of oropharynx
Tongue
Lingual frenulum
Opening of
submandibular duct
Gingivae (gums)
Inferior labial
frenulum
(b) Anterior view
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Figure 22.7b
29.
Palate
• Hard palate: palatine bones and palatine
processes of the maxillae
• Slightly corrugated to help create friction
against the tongue
• Soft palate: fold formed mostly of skeletal
muscle
• Closes off the nasopharynx during swallowing
• Uvula projects downward from its free edge
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30. Tongue
• Functions include
• Repositioning and mixing food during chewing
• Formation of the bolus
• Initiation of swallowing, speech, and taste
• Intrinsic muscles change the shape of the tongue
• Extrinsic muscles alter the tongue’s position
• Lingual frenulum: attachment to the floor of the
mouth
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31. Tongue
•
Surface bears papillae
•
taste buds
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Epiglottis
Palatopharyngeal
arch
Palatine tonsil
Lingual tonsil
cluster of lymphoid follicles
Palatoglossal
arch
Terminal sulcus
Foliate papillae
Circumvallate
papilla
Midline groove
of tongue
Dorsum of tongue
32
Fig.
23.8
Page
860
Fungiform papilla
Filiform papilla
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Figure 22.8
33.
Salivary Glands
• Extrinsic salivary glands (parotid,
submandibular, and sublingual)
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34.
Salivary Glands
• Intrinsic (buccal) salivary glands are scattered
in the oral mucosa - no ducts
• Secretion (saliva)
• Cleanses the mouth
• Moistens and dissolves food chemicals
• Aids in bolus formation
• Contains enzymes that begin the breakdown
of starch (amylase)
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35.
Salivary Glands
• Parotid gland
• Anterior to the ear external to the masseter
muscle
• Parotid duct opens into the vestibule next to
second upper molar
• Submandibular gland
• Medial to the body of the mandible
• Duct opens at the base of the lingual frenulum
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36.
Salivary Glands
• Sublingual gland
• Anterior to the submandibular gland under the
tongue
• Opens via 10–12 ducts into the floor of the
mouth
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37
Fig. 23.9 page 861
Tongue
Teeth
Parotid
gland
Ducts of
sublingual
gland
Frenulum
of tongue
Sublingual
gland
Mylohyoid
muscle (cut)
Anterior belly of
digastric muscle
(a)
Submandibular
gland
Parotid duct
Masseter muscle
Body of
mandible (cut)
Posterior belly
of digastric
muscle
Submandibular
duct
Mucous
cells
(b)
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Serous cells
forming
demilunes
Figure 22.9
38.
Composition of Saliva
• Secreted by serous and mucous cells
• 97–99.5% water, slightly acidic solution
containing
• Salivary amylase and lingual lipase
PLAY
Animation: Rotatable head
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39.
Control of Salivation
• Intrinsic glands continuously keep the mouth
moist
• Extrinsic salivary glands produce secretions
when
• Ingested food stimulates chemoreceptors and
mechanoreceptors in the mouth - Smell
• Strong sympathetic stimulation inhibits
salivation and results in dry mouth
(xerostomia)
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40.
Teeth
• Primary and permanent dentitions are formed
by age 21
• 20 deciduous teeth erupt (6–24 months of
age)
• Roots are resorbed, teeth fall out (6–12 years
of age) as permanent teeth develop
• 32 permanent teeth
• All except third molars erupt by the end of
adolescence
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41
(b)
Figure 23.10; page 862
Deciduous teeth
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Permanent teeth
Figure 22.10b
42.
Classes of Teeth
• 2I, 1C, 2P, 3M
• Incisors
• Chisel shaped for cutting
• Canines
• Fanglike teeth that tear or pierce
• Premolars (bicuspids) and molars
• Have broad crowns with rounded cusps for
grinding or crushing
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43
Figure 23.10; page 863
Incisors
Central (6–8 mo)
Lateral (8–10 mo)
Canine (eyetooth)
(16–20 mo)
Molars
First molar
(10–15 mo)
Second molar
(about 2 yr)
(a)
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Deciduous
(milk) teeth
Incisors
Central (7 yr)
Lateral (8 yr)
Canine (eyetooth)
(11 yr)
Premolars
(bicuspids)
First premolar
(11 yr)
Second premolar
(12–13 yr)
Molars
First molar (6–7 yr)
Second molar
(12–13 yr)
Third molar
(wisdom tooth)
(17–25 yr)
Permanent
teeth
Figure 22.10a
44.
Tooth Structure
• Crown: the exposed part above the gingiva
(gum)
• Covered by enamel—the hardest substance in
the body (calcium salts and hydroxyapatite
crystals)
• Root: portion embedded in the jawbone
• Connected to crown by neck
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45.
Tooth Structure
• Cementum: calcified connective tissue
• Covers root and attaches it to the periodontal
ligament
• Periodontal ligament
• Forms fibrous joint called a gomphosis
• Gingival sulcus: groove where gingiva borders
the tooth
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46.
Tooth Structure
• Dentin: bonelike material under enamel
• Maintained by odontoblasts of pulp cavity
• Pulp cavity: cavity surrounded by dentin
• Pulp: connective tissue, blood vessels, and
nerves
• Root canal: extends from pulp cavity to the
apical foramen of the root
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Crown
Neck
Root
Enamel
Dentin
Dentinal tubules
Pulp cavity (contains
blood vessels and
nerves)
Gingiva (gum)
Cementum
47
Root canal
Periodontal
ligament
Figure:
23.11
Page: 863
Apical foramen
Bone
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Figure 22.11
48.
Tooth and Gum Disease
• Dental caries (cavities): gradual
demineralization of enamel and dentin
• Dental plaque (sugar, bacteria, and debris)
adheres to teeth
• Acid from bacteria dissolves calcium salts
• Proteolytic enzymes digest organic matter
• Prevention: daily flossing and brushing
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49.
Tooth and Gum Disease
• Gingivitis
• Plaque calcifies to form calculus (tartar)
• Calculus disrupts the seal between the
gingivae and the teeth
• Anaerobic bacteria infect gums
• Infection reversible if calculus removed
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50.
Tooth and Gum Disease
• Periodontitis
• Immune cells attack intruders and body tissues
• Destroy periodontal ligament
• Activate osteoclasts
• Consequences
• Possible tooth loss, promotion of
atherosclerosis and clot formation in
coronary and cerebral arteries
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