1. 23
The Digestive System: Part A

2. Two groups of organs Digestive System
1. Alimentary canal (gastrointestinal or GI tract)
Mouth to anus
Digests food and absorbs fragments
Mouth, pharynx, esophagus, stomach, small intestine, and large intestine
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3. 2. Accessory digestive organs
Digestive System
2. Accessory digestive organs
Teeth, tongue, gallbladder
Digestive glands
Salivary glands
Liver
Pancreas
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4. Mouth (oral cavity) Parotid gland Sublingual gland Salivary Tongue*
Figure Alimentary canal and related accessory digestive organs.
Mouth (oral cavity)
Parotid gland
Sublingual gland
Salivary
glands*
Tongue*
Submandibular gland
Pharynx
Esophagus
Stomach
Pancreas*
(Spleen)
Liver*
Gallbladder*
Transverse colon
Duodenum
Descending colon
Small
intestine
Jejunum
Ascending colon
Ileum
Cecum
Large
intestine
Sigmoid colon
Rectum
Appendix
Anus
Anal canal
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5. Six essential activities
Digestive Processes
Six essential activities
Ingestion
Propulsion
Mechanical breakdown
Digestion
Absorption
Defecation
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6. Ingestion Food Mechanical breakdown Pharynx Esophagus Chewing (mouth)
Figure Gastrointestinal tract activities.
Ingestion
Food
Mechanical
breakdown
Pharynx
Esophagus
Chewing (mouth)
Churning (stomach)
Propulsion
Segmentation
(small intestine)
• Swallowing
(oropharynx)
• Peristalsis
(esophagus,
stomach,
small intestine,
large intestine)
Digestion
Stomach
Absorption
Lymph
vessel
Small
intestine
Blood
vessel
Large
intestine
Mainly H2O
Feces
Anus
Defecation
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7. Figure 23.3 Peristalsis and segmentation.
From
mouth
Peristalsis: Adjacent segments of alimentary tract organs alternately contract and relax, moving food along the tract distally.
Segmentation: Nonadjacent segments of alimentary tract organs alternately contract and relax, moving food forward then backward.
Food mixing and slow food propulsion occur.
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8. Peritoneum and Peritoneal Cavity
Peritoneum - serous membrane of abdominal cavity
Visceral peritoneum on external surface of most digestive organs
Parietal peritoneum lines body wall
Peritoneal cavity
Between two peritoneums
Fluid lubricates mobile organs
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9. Two schematic cross sections of abdominal cavity illustrate
Figure 23.5a The peritoneum and the peritoneal cavity.
Abdominopelvic
cavity
Vertebra
Dorsal
mesentery
Parietal
peritoneum
Ventral
mesentery
Visceral
peritoneum
Peritoneal
cavity
Alimentary
canal organ
Liver
Two schematic cross sections of abdominal cavity illustrate
the peritoneums and mesenteries.
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10. Peritoneum and Peritoneal Cavity
Mesentery - double layer of peritoneum
Routes for blood vessels, lymphatics, and nerves
Holds organs in place; stores fat
Retroperitoneal organs posterior to peritoneum
Intraperitoneal (peritoneal) organs surrounded by peritoneum
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12. Homeostatic Imbalance
Peritonitis
Inflammation of peritoneum
Causes by e.g., piercing abdominal wound, perforating ulcer, ruptured appendix
Peritoneal coverings stick together, localizing infection
Dangerous and lethal if widespread
Treated with debris removal and antibiotics
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13. Blood Supply: Splanchnic Circulation
Branches of aorta serving digestive organs
Hepatic, splenic, and left gastric arteries
Inferior and superior mesenteric arteries
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)
Mucosa
Submucosa
Muscularis externa
Serosa
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15. Myenteric nerve plexus
Figure Basic structure of the alimentary canal.
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
(mesothelium)
Nerve
Connective tissue
Artery
Gland in mucosa
Lumen
Vein
Duct of gland outside
alimentary canal
Mucosa-associated
lymphoid tissue
Mesentery
Lymphatic vessel
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16. Functions – different layers perform 1 or all 3
Mucosa
Lines lumen
Functions – different layers perform 1 or all 3
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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17. Mucosa
Epithelium
Simple columnar epithelium and mucus-secreting cells (most of tract)
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. Muscularis mucosae: smooth muscle  local movements of mucosa
Lamina propria
Loose areolar connective tissue
Capillaries for nourishment and absorption
Lymphoid follicles (part of MALT)
Defend against microorganisms
Muscularis mucosae: smooth muscle  local movements of mucosa
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19. Submucosa Submucosa Areolar connective tissue
Blood and lymphatic vessels, lymphoid follicles, and submucosal nerve plexus
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20. Muscularis Externa Muscularis externa
Responsible for segmentation and peristalsis
Inner circular and outer longitudinal layers
Circular layer thickens in some areas  sphincters
Myenteric nerve plexus between two muscle layers
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21. Serosa Visceral peritoneum
Areolar connective tissue covered with mesothelium in most organs
Replaced by fibrous adventitia in esophagus
Retroperitoneal organs have both an adventitia and serosa
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22. Myenteric nerve plexus
Figure Basic structure of the alimentary canal.
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
(mesothelium)
Nerve
Connective tissue
Artery
Gland in mucosa
Lumen
Vein
Duct of gland outside
alimentary canal
Mucosa-associated
lymphoid tissue
Mesentery
Lymphatic vessel
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23. Functional Anatomy: Mouth
Oral (buccal) cavity
Bounded by lips, cheeks, palate, and tongue
Oral orifice is anterior opening
Lined with stratified squamous epithelium
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24. Sagittal section of the oral cavity and pharynx
Figure 23.7a Anatomy of the oral cavity (mouth).
Soft
palate
Palatoglossal
arch
Uvula
Hard
palate
Oral cavity
Palatine
tonsil
Tongue
Oropharynx
Lingual tonsil
Epiglottis
Hyoid bone
Laryngopharynx
Esophagus
Trachea
Sagittal section of the oral cavity and pharynx
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25. Upper lip Gingivae (gums) Superior labial frenulum Palatine raphe
Figure 23.7b Anatomy of the oral cavity (mouth).
Upper lip
Gingivae
(gums)
Superior
labial
frenulum
Palatine
raphe
Palatoglossal
arch
Hard
palate
Palatopharyngeal
arch
Soft
palate
Uvula
Palatine
tonsil
Posterior wall
of oropharynx
Tongue
Sublingual
fold with
openings of
sublingual
ducts
Lingual frenulum
Opening of
Submandibular
duct
Gingivae (gums)
Oral vestibule
Inferior labial
frenulum
Lower lip
Anterior view
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26. Hard palate - palatine bones and palatine processes of maxillae
Slightly corrugated to help create friction against tongue
Soft palate - fold formed mostly of skeletal muscle
Closes off nasopharynx during swallowing
Uvula projects downward from its free edge
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27. Intrinsic muscles change shape of tongue
Skeletal muscle
Functions include
Repositioning and mixing food during chewing
Formation of bolus
Initiation of swallowing, speech, and taste
Intrinsic muscles change shape of tongue
Extrinsic muscles alter tongue's position
Lingual frenulum: attachment to floor of mouth
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28. Surface bears papillae
Tongue
Surface bears papillae
Filiform—whitish, give the tongue roughness and provide friction; do not contain taste buds
Fungiform—reddish, scattered over tongue; contain taste buds
Vallate (circumvallate)—V-shaped row in back of tongue; contain taste buds
Foliate—on lateral aspects of posterior tongue; contain taste buds that function primarily in infants and children
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29. Terminal sulcus marks division between
Tongue
Lingual lipase
Fat-digesting enzyme functional in stomach
Terminal sulcus marks division between
Body - anterior 2/3 residing in oral cavity
Root - posterior third residing in oropharynx
Just posterior to vallate papillae
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30. Epiglottis Palatopharyngeal arch Palatine tonsil Lingual tonsil
Figure Dorsal surface of the tongue, and the tonsils.
Epiglottis
Palatopharyngeal
arch
Palatine tonsil
Lingual tonsil
Palatoglossal
arch
Terminal sulcus
Foliate papillae
Vallate papilla
Medial sulcus
of the tongue
Dorsum of tongue
Fungiform papilla
Filiform papilla
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31. Salivary Glands Major salivary glands Minor salivary glands
Produce most saliva; lie outside oral cavity
Parotid
Submandibular
Sublingual
Minor salivary glands
Scattered throughout oral cavity; augment slightly
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32. Salivary Glands Function of saliva Cleanses mouth
Dissolves food chemicals for taste
Moistens food; compacts into bolus
Begins breakdown of starch with enzymes
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33. Salivary Glands Parotid gland
Anterior to ear; external to masseter muscle
Parotid duct opens into oral vestibule next to second upper molar
Mumps is inflammation of parotid glands
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34. Salivary Glands Submandibular gland Sublingual gland
Medial to body of mandible
Duct opens at base of lingual frenulum
Sublingual gland
Anterior to submandibular gland under tongue
Opens via 10–12 ducts into floor of mouth
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35. Figure 23.9 The salivary glands.
Tongue
Teeth
Parotid
gland
Ducts of
sublingual
gland
Parotid duct
Masseter muscle
Frenulum
of tongue
Body of mandible (cut)
Sublingual
gland
Posterior belly of
digastric muscle
Mylohyoid
muscle (cut)
Submandibular
duct
Anterior belly of
digastric muscle
Submandibular
gland
Mucous cells
Serous cells
forming demilunes
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36. TEETH: THE BEGINNING OF DIGESTION

37. Tear and grind food for digestion
Teeth
Tear and grind food for digestion
Primary and permanent dentitions formed by age 21
20 deciduous teeth erupt (6–24 months of age)
Roots resorbed, teeth fall out (6–12 years of age) as permanent teeth develop
32 permanent teeth
All but third molars in by end of adolescence
Third molars at 17–25, or may not erupt
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38. Premolars (bicuspids) Molars
Classes of Teeth
Incisors
Chisel shaped for cutting
Canines
Fanglike teeth that tear or pierce
Premolars (bicuspids)
Broad crowns, rounded cusps – grind/crush
Molars
Broad crowns, rounded cusps – best grinders
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39. Figure 23.10 Human dentition.
Incisors
Central (6–8 mo)
Lateral (8–10 mo)
Canine (eyetooth)
(16–20 mo)
Molars
First molar
(10–15 mo)
Deciduous
(milk) teeth
Second molar
(about 2 yr)
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
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40. Enamel Dentin Cement Root canal Bone
Figure Longitudinal section of a canine tooth within its bony socket (alveolus).
Enamel
Dentin
Crown
Dentinal
tubules
Pulp cavity
(contains
blood vessels
and nerves)
Neck
Gingival
sulcus
Gingiva
(gum)
Cement
Root canal
Root
Periodontal
ligament
Apical
foramen
Bone
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41. NOTES – TEETH: THE BEGINNING OF DIGESTION
Parts of Teeth
Dentin
most of the tooth
matrix similar to bone except no living cells

42. Enamel
calcium phosphate
hardest substance produced by the body

43. Pulp Cavity
blood vessels & nerves – enter through root foramen (opening) at base of tooth

44. Other tooth parts/stuff
crown, neck, root, gum or GINGIVA

45. deciduous (baby) teeth – 20 by age 2

46. Adult teeth - 32
note locations of incisors, canines, premolars, molars

47. Problems with Teeth
Plaque
bacteria sticking to surface of teeth – produces sticky matrix that traps food particles
this protects bacteria from saliva

48. Cavities
acid from bacteria erode the structure of the tooth
can be prevented by brushing and FLOSSING

49. bacteria infect pulp – destroy pulp cavity and nerve
Root Canal
pulp must be removed and packed with solid materials

50. Tooth and Gum Disease
Dental caries (cavities) - demineralization of enamel and dentin from bacterial action
Dental plaque (film of 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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51. Tooth and Gum Disease Gingivitis
Plaque calcifies to form calculus (tartar)
Calculus disrupts seal between gingivae and teeth
Anaerobic bacteria infect gums
Infection reversible if calculus removed
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52. Periodontitis (from neglected gingivitis)
Tooth and Gum Disease
Periodontitis (from neglected gingivitis)
Immune cells attack intruders and body tissues
Destroy periodontal ligament
Activate osteoclasts  dissolve bone
Possible tooth loss; may promote atherosclerosis and clot formation in coronary and cerebral arteries
Risk factors - smoking, diabetes mellitus, oral piercing
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