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. 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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9. Histology of the Alimentary Canal
Four basic layers (tunics)
Mucosa
Submucosa
Muscularis externa
Serosa
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10. 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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11. 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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12. 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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13. 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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14. 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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15. 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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16. 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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17. 97–99.5% water, slightly acidic
Composition of Saliva
97–99.5% water, slightly acidic
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
PLAY
Animation: Rotating head
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