Chapter 18
Digestive System
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Digestive System
• Food must be converted by physical and
chemical changes before it can be used by
the cells; this process is called digestion
• Enzymes
• Alimentary canal
• Accessory organs
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or duplicated, or posted to a publicly accessible website, in whole or in part.
Layers of the Digestive System
(1 of 2)
• Mucosa
– Innermost lining
• Submucosa
• Muscularis
− Skeletal and smooth muscle
• Serosa (visceral peritoneum)
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Lining of the Digestive System
(2 of 2)
• Peritoneum
–
–
–
–
Parietal
Visceral
Mesentery
Greater omentum
• Peritonitis
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Functions of the Digestive System
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Break down food physically
Peristalsis
Change food chemically
Absorb the nutrients
Eliminate the waste products of digestion
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Figure 18-1 Structures of the
digestive system
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Organs of Digestion
• Mouth (oral or buccal cavity)
• Tongue/accessory organ of digestion
• Salivary glands
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Teeth/Accessory
Organ of Digestion
• Gingivae or gums
• Teeth
– Food chewed or masticated
– Deciduous and permanent teeth
• Structure of the tooth
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Figure 18-2 Structures of the tongue and oral cavity
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Esophagus
• Muscular tube to transport swallowed food
to stomach
• Esophageal wall layers
–
–
–
–
Mucosa
Submucosa
Muscular
External serous
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Stomach (1 of 2)
• Fundus
– Upper part
• Body or great curvature
– Middle section
• Pylorus
– Lower portion
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Stomach (2 of 2)
• Sphincters
– Cardiac sphincter
– Pyloric sphincter
• Four layers of the stomach wall
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Figure 18-5 The parts of the stomach
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Gastric Juices (1 of 2)
• Enteroendocrine glands
– Secrete gastrin- stimulates production of HCL and pepsinogen
• Parietal cells
– Produce HCL and intrinsic factor, converts pepsinogen into
pepsin
• Chief type cells
– Produce pepsinogen
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Gastric Juices (2 of 2)
• Mucus cells
– Secrete alkaline mucus which neutralizes HCL
• Rennin
– Found in infants and children
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Small Intestine
•
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•
About 20 feet long
Same four layers as the stomach
Duodenum (first segment-12 inches)
Jejunum (middle segment-8 feet long)
Ileum (last segment-10–12 feet)
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Figure 18-6 Small intestine
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Digestive Juices in
the Small Intestine
•
•
•
•
Enzymes, secretin, and cholecystokinin
Pancreatic juices, protease and lipase
Bile
Intestinal juices
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Absorption in the Small Intestine
• Villi
– Makes absorption possible
– Increases the surface area
• Each villi contains a network of blood and
lymph capillaries
• Digested portion passes through the villi
into the bloodstream and lacteals
• Undigested portion passes on to the large
intestine
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or duplicated, or posted to a publicly accessible website, in whole or in part.
Accessory Organs of Digestion
• Pancreas
• Liver
• Gallbladder
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or duplicated, or posted to a publicly accessible website, in whole or in part.
Figure 18-9 The structure of the pancreas, showing both exocrine
and endocrine portions
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or duplicated, or posted to a publicly accessible website, in whole or in part.
Figure 18-10 Liver, gallbladder, and pancreas
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Large Intestine (1 of 2)
• Also called the colon
• About 5 feet long
• Ileum empties chyme through ileocecal
valve into large intestine
• Haustra are pockets that increase surface
area
• Secretes mucus to lubricate passageway
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Large Intestine (2 of 2)
• Cecum and appendix
• Ascending, transverse, and descending
colon
• Sigmoid colon
• Anal canal
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Figure 18-11 The structure of the large intestine
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General Overview of Digestion
(1 of 2)
•
•
•
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Bolus
Peristalsis
Digestion of protein, fats, and carbohydrates
Absorption of nutrients
Undigested substance – feces
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General Overview of Digestion
(2 of 2)
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Action in the mouth
Action in the pharynx
Action in the esophagus
Action in the stomach
Action in the small intestine
Action in the large intestine
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Action in the Large Intestine
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Absorption
Bacterial action
Gas formation
Fecal formation
Defecation
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Effects of Aging
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Decrease sensory ability of taste buds
Reduction of saliva
Loss of teeth
Slowing peristalsis
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Metabolism (1 of 2)
• Within the cells, nutrients are changed into
energy
• Aerobic metabolism
– Oxidation
• Anaerobic metabolism
– Krebs cycle
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Metabolism (2 of 2)
• Anabolism and catabolism
• Thyroid hormones
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Common Symptoms of Digestive
Disorders
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Nausea
Vomiting
Constipation
Diarrhea
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Disorders of the Digestive System
(1 of 5)
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Cleft lip/palate
Gingivitis
Periodontal disease
Gastroesophageal reflux disease (GERD)
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Disorders of the Digestive System
(2 of 5)
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•
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Hiatal hernia
Heartburn
Pyloric stenosis
Gastritis
Gastroenteritis
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Disorders of the Digestive System
(3 of 5)
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Enteritis
Ulcer
Inflammatory bowel disease (IBD)
Appendicitis
Hepatitis
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Disorders of the Digestive System
(4 of 5)
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Cirrhosis
Cholecystitis
Gallstones
Pancreatitis
Diverticulosis
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Disorders of the Digestive System
(5 of 5)
• Hemorrhoids
• Cancer
– Stomach
– Colorectal
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or duplicated, or posted to a publicly accessible website, in whole or in part.