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PowerPoint® Lecture Slides prepared by Janice Meeking, Mount Royal College
C H A P T E R
Copyright © 2010 Pearson Education, Inc.
23
The Digestive System: Part A
Copyright © 2010 Pearson Education, Inc.
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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Digestive System
2. Accessory digestive organs
• Teeth, tongue, gallbladder
• Digestive glands
• Salivary glands
• Liver
• pancreas
Copyright © 2010 Pearson Education, Inc. Figure 23.1
Mouth (oral cavity)Tongue
Esophagus
LiverGallbladder
Anus
DuodenumJejunumIleum
Small intestine
Parotid glandSublingual glandSubmandibulargland
Salivaryglands
PharynxStomachPancreas(Spleen)
Transverse colonDescending colonAscending colonCecumSigmoid colonRectumVermiform appendixAnal canal
Largeintestine
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Digestive Processes
• Six essential activities
1. Ingestion
2. Propulsion
3. Mechanical digestion
4. Chemical digestion
5. Absorption
6. Defecation
Copyright © 2010 Pearson Education, Inc. Figure 23.2
FoodIngestion
PropulsionEsophagus
Stomach
PharynxMechanicaldigestion
Chemicaldigestion
• Chewing (mouth)• Churning (stomach)• Segmentation (small intestine)
Smallintestine Largeintestine
Defecation Anus
Feces
Bloodvessel
Lymphvessel
Absorption
• Swallowing (oropharynx)• Peristalsis (esophagus, stomach, small intestine, large intestine)
Mainly H2O
Copyright © 2010 Pearson Education, Inc. Figure 23.3
Frommouth
(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.
(a) Peristalsis: Adjacent segments ofalimentary tract organs alternately contractand relax, which moves food along the tractdistally.
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GI tract regulatory mechanisms
1. Mechanoreceptors and chemoreceptors
• Respond to stretch, changes in osmolarity and pH, and presence of substrate and end products of digestion
• Initiate reflexes that• Activate or inhibit digestive glands
• Stimulate smooth muscle to mix and move lumen contents
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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
Copyright © 2010 Pearson Education, Inc. Figure 23.4
External stimuli(sight, smell, taste,
thought of food)Central nervous system
and extrinsic autonomic nerves
Afferent impulses Efferent impulses
Long reflexes
Internal(GI tract)stimuli
Chemoreceptors,osmoreceptors, ormechanoreceptors
Local (intrinsic)nerve plexus(“gut brain”)
Effectors:Smooth muscle
or glands
Gastrointestinalwall (site of shortreflexes)
Response:Change in
contractile orsecretory activityLumen of the
alimentary canal
Short reflexes
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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
Copyright © 2010 Pearson Education, Inc. Figure 23.5a
Peritonealcavity
Parietalperitoneum
Visceralperitoneum
Ventralmesentery
Abdominopelviccavity
Dorsalmesentery
Vertebra
Alimentarycanal organ
(a) Schematic cross sections of abdominal cavity illustrate the peritoneums and mesenteries.
Liver
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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
Copyright © 2010 Pearson Education, Inc. Figure 23.5b
Abdominopelviccavity
Mesenteryresorbedand lost
(b) Some organs lose their mesentery and become retroperitoneal during development.
Alimentarycanal organ
Alimentary canal organ ina retroperitoneal position
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Blood Supply: Splanchnic Circulation
• Arteries• 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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Histology of the Alimentary Canal
• Four basic layers (tunics)• Mucosa
• Submucosa
• Muscularis externa
• Serosa
Copyright © 2010 Pearson Education, Inc. Figure 23.6
Glands in submucosa
Submucosa
LumenMucosa-associatedlymphoid tissue
Duct of gland outsidealimentary canal
Gland in mucosa
NerveArteryVein
Lymphaticvessel Mesentery
Intrinsic nerve plexuses• Myenteric nerve plexus• Submucosal nerve plexus
Mucosa• Epithelium• Lamina propria• Muscularis mucosae
Muscularis externa• Longitudinal muscle • Circular muscleSerosa• Epithelium• Connective tissue
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Mucosa
• Lines the lumen • Functions• Secretes mucus, digestive enzymes and
hormones• Absorbs end products of digestion• Protects against infectious disease
• Three sublayers: epithelium, lamina propria, and muscularis mucosae
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Mucosa
• Epithelium• Simple columnar epithelium and mucus-
secreting 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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Mucosa
• Lamina propria• Loose areolar connective tissue
• Capillaries for nourishment and absorption
• Lymphoid follicles (part of MALT)
• Muscularis mucosae: smooth muscle that produces local movements of mucosa
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Submucosa and Muscularis Externa
• Submucosa• Dense connective tissue
• Blood and lymphatic vessels, lymphoid follicles, and submucosal nerve plexus
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Submucosa and Muscularis Externa
• Muscularis externa• Responsible for segmentation and peristalsis
• Inner circular and outer longitudinal layers
• Myenteric nerve plexus
• Sphincters in some regions
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Serosa
• Visceral peritoneum• Replaced by the fibrous adventitia in the
esophagus
• Retroperitoneal organs have both an adventitia and serosa
Copyright © 2010 Pearson Education, Inc. Figure 23.6
Glands in submucosa
Submucosa
LumenMucosa-associatedlymphoid tissue
Duct of gland outsidealimentary canal
Gland in mucosa
NerveArteryVein
Lymphaticvessel Mesentery
Intrinsic nerve plexuses• Myenteric nerve plexus• Submucosal nerve plexus
Mucosa• Epithelium• Lamina propria• Muscularis mucosae
Muscularis externa• Longitudinal muscle • Circular muscleSerosa• Epithelium• Connective tissue
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Enteric Nervous System
• Intrinsic nerve supply of the alimentary canal• Submucosal nerve plexus
• Regulates glands and smooth muscle in the mucosa
• Myenteric nerve plexus
• Controls GI tract motility
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Enteric Nervous System
• Linked to the CNS via afferent visceral fibers
• Long ANS fibers synapse with enteric plexuses• Sympathetic impulses inhibit secretion and
motility
• Parasympathetic impulses stimulate
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Mouth
• Oral (buccal) cavity• Bounded by lips, cheeks, palate, and tongue
• Oral orifice is the anterior opening
• Lined with stratified squamous epithelium
Copyright © 2010 Pearson Education, Inc. Figure 23.7a
UvulaSoft palate Palatoglossal arch
Palatine tonsil
Hard palate
Oral cavity
Tongue
Lingual tonsilOropharynx
EpiglottisHyoid boneLaryngopharynx
Esophagus
Trachea(a) Sagittal section of the oral cavity and pharynx
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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
Copyright © 2010 Pearson Education, Inc. Figure 23.7b
UvulaPalatine tonsil
Sublingual foldwith openings ofsublingual ducts
Tongue
Upper lip
Lower lipVestibule
Gingivae (gums)
Gingivae (gums)
Hard palateSoft palate
Lingual frenulumOpening ofsubmandibular duct
Palatine raphe
Inferior labialfrenulum
Posterior wallof oropharynx
Palatopharyngealarch
Superior labialfrenulumPalatoglossal arch
(b) Anterior view
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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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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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Copyright © 2010 Pearson Education, Inc.
Tongue
• Surface bears papillae
1. Filiform—whitish, give the tongue roughness and provide friction- have keratin in the cells
2. Fungiform—reddish, scattered over the tongue
3. Circumvallate (vallate)—V-shaped row in back of tongue
4. Foliate—on the lateral aspects of the posterior tongue
Note: The Fungiform, Circumvallate and Foliate house taste buds
Go To Taste PowerPoint
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Tongue
• Terminal sulcus marks the division between• Body: anterior 2/3 residing in the oral cavity
• Root: posterior third residing in the oropharynx
Copyright © 2010 Pearson Education, Inc. Figure 23.8
EpiglottisPalatopharyngealarchPalatine tonsilLingual tonsilPalatoglossalarch
Foliate papillaeCircumvallatepapilla
Terminal sulcus
Dorsum of tongue
Midline grooveof tongue
Filiform papillaFungiform papilla
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SALIVA
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Salivary Glands (Two groups)
• Extrinsic salivary glands - (parotid, submandibular, and sublingual)
• Intrinsic (buccal ) salivary glands - scattered in the oral mucosa
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Saliva Functions
• Cleanses the mouth
• Moistens and dissolves food chemicals
• Aids in bolus formation
• Contains enzymes that begin the breakdown of starch
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Extrinsic Salivary Glands
• Parotid gland (Otic Ganglion – CN IX)• Anterior to the ear external to the masseter
muscle
• Parotid duct opens into the vestibule next to second upper molar
• Submandibular gland (Submandibular Ganglion CN VII)• Medial to the body of the mandible
• Duct opens at the base of the lingual frenulum
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Salivary Glands
• Sublingual gland (Submandibular Ganglion CN VII)• Anterior to the submandibular gland under the
tongue
• Opens via 10–12 ducts into the floor of the mouth
Copyright © 2010 Pearson Education, Inc. Figure 23.9
Teeth
Ducts ofsublingualgland
Sublingualgland
Submandibularduct
Posterior bellyof digastric muscle
Parotid ductMasseter muscleBody ofmandible (cut)
Parotidgland
Tongue
Submandibulargland
(a)
Frenulumof tongue
Mylohyoidmuscle (cut)Anterior belly ofdigastric muscle Mucous
cells (b)
Serous cellsforming demilunes
Copyright © 2010 Pearson Education, Inc. Figure 23.7b
UvulaPalatine tonsil
Sublingual foldwith openings ofsublingual ducts
Tongue
Upper lip
Lower lipVestibule
Gingivae (gums)
Gingivae (gums)
Hard palateSoft palate
Lingual frenulumOpening ofsubmandibular duct
Palatine raphe
Inferior labialfrenulum
Posterior wallof oropharynx
Palatopharyngealarch
Superior labialfrenulumPalatoglossal arch
(b) Anterior view
Copyright © 2010 Pearson Education, Inc.Figure 14.4
Copyright © 2010 Pearson Education, Inc.Figure 14.5
Copyright © 2010 Pearson Education, Inc.
Saliva is secreted by serous and mucous cells• Serous cells produce a watery secretion containing
enzymes, ions, and tiny bit of mucin.
• Mucous cells produce mucin – a glycoprotein substance that when mixed with water produces mucous.
• The parotid gland only has serous cells.
• Submandibular and buccal glands produce equal proportions of serous and mucous
• Sublingual glands only produce mucous
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Composition of Saliva
• 97–99.5% water, slightly acidic solution containing
• Electrolytes—Na+, K+, Cl–, PO4 2–, HCO3–
• Salivary amylase and lingual lipase
• Mucin
• Metabolic wastes—urea and uric acid
• Lysozyme, IgA, defensins, and a cyanide compound protect against microorganisms
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Additional Data on Saliva• Normal flora in the mouth convert food-derived
nitrates into nitrites which in-turn convert to nitric oxide in an acidic environment. This transformation occurs around the gums, where acid producing bacteria tend to cluster, and in the HCl rich secretions of the stomach. This activity acts as bacteriocidal agents in these locations.
• Saliva tests for HIV antibodies, oral cancer and diabetes are available
• Quick assessments of body hormones can be performed on saliva
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Control of Salivation (1)• Intrinsic glands continuously keep the mouth moist
• Extrinsic salivary glands produce secretions when • Ingested food stimulates chemoreceptors and
mechanoreceptors in the mouth – chemoreceptors are activated more strongly by acids like vinegar and citrus juice – mechanoreceptors are stimulated by any object in the mouth
• Sight or smell of food is enough to get juices flowing
• Irritations of lower GI by bacterial toxins, spicy foods or hyperacidity especially when associated feeling of nausea – also increases salivation
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Control of Salivation (2)
• Salivatory nuclei in the brain stem (Pons and Medulla) send impulses along parasympathetic fibers in cranial nerves VII and IX
• Strong sympathetic stimulation inhibits salivation and results in dry mouth (xerostomia)
• Average output of saliva is 1 to 1 ½ liter per day
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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
Copyright © 2010 Pearson Education, Inc. Figure 23.10b
Deciduous teeth Permanent teeth(b)
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Classes of Teeth
• 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
Copyright © 2010 Pearson Education, Inc. Figure 23.10a
IncisorsCentral (6–8 mo)
IncisorsCentral (7 yr)
Canine (eyetooth)(16–20 mo)
Canine (eyetooth)(11 yr)Premolars(bicuspids)First premolar(11 yr)
MolarsFirst molar(10–15 mo)
MolarsFirst molar (6–7 yr)
Lateral (8–10 mo) Lateral (8 yr)
Second molar(about 2 yr)
Second molar(12–13 yr)Third molar(wisdom tooth)(17–25 yr)(a)
Permanentteeth
Deciduous(milk) teeth Second premolar
(12–13 yr)
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Dental Formulas
• A shorthand way of indicating the number and relative position of teeth• Ratio of upper to lower teeth for one-half of the
mouth
• Primary: 2I,1C, 2M
• Permanent: 2I,1C, 2PM, 3M
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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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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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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
Copyright © 2010 Pearson Education, Inc. Figure 23.11
Crown
Neck
Root
EnamelDentinDentinal tubulesPulp cavity (containsblood vessels and nerves)Gingiva (gum)
CementumRoot canalPeriodontalligament
Apical foramen
Bone
Copyright © 2010 Pearson Education, Inc.
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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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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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