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Chapter 16
Nutrition and the Digestive
System
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Introduction
• Digestion: breakdown of food into smaller,
usable form
– Ingestion
– Peristalsis
– Digestion
– Absorption
– Defecation
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General Organization
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General Organization (cont’d.)
• Gastrointestinal tract
– Mouth, pharynx, esophagus, stomach, small
intestine, large intestine
• Accessory organs
– Teeth, tongue, salivary glands, liver,
gallbladder, pancreas
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General Organization (cont’d.)
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Histology
• Tunics (from the inside out)
– Mucosa: mucous membrane attached to thin
layer of visceral muscle
– Submucosa: loose connective tissue
– Muscularis: skeletal or smooth muscle
– Adventitia: serous membrane made of
connective and epithelial tissue
• Also called visceral peritoneum
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The Mouth or Oral Cavity
• Functions
– Taste
– Mechanical breakdown of food
– Chemical digestion of carbohydrates
• Amylase
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The Mouth or Oral Cavity (cont’d.)
• Structure
– Cavity lined with mucous membrane
– Cavity floor formed by tongue
– Cavity roof formed by hard and soft palate
– Cavity sides formed by cheeks
– Cavity opening guarded by lips
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The Mouth or Oral Cavity (cont’d.)
• Functions of tongue
– Food manipulation, taste, speech
• Structure of tongue
– Skeletal muscle covered with mucous
membrane
– Lingual frenulum
– Papillae
• Taste buds
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The Mouth or Oral Cavity (cont’d.)
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The Salivary Glands
• Pairs of salivary glands
– Parotid, submandibular, sublingual
• Saliva
– Is 99.5% water
– Has amylase, which digests carbohydrates
– Is buffered by bicarbonates and phosphates
– Has mucin to lubricate food
– Has lysozyme to destroy bacteria
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The Salivary Glands (cont’d.)
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Teeth
• Structure: crown, neck, root
• Crown covered in enamel
• Dentin: bonelike substance enclosing pulp
cavity
• Cementum: covers root
• Periodontal ligament: anchors tooth
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Teeth (cont’d.)
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The Pharynx
• Common passageway for food and air
• Divisions
– Nasopharynx, oropharynx, laryngopharynx
• Function: begins swallowing (deglutition)
– Forms food bolus
– Air passageways close
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The Esophagus
• Function
– Secrete mucus
– Transport food
• Peristalsis: smooth muscle contractions
push food
• Lower esophageal sphincter
– Controls passage of food into stomach
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The Stomach
• Functions: chemical and mechanical
breakdown of food
• Parts
– Cardia, fundus, body, pylorus
• Gastric glands: secretory cells
– Zymogenic, parietal, mucous
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The Stomach (cont’d.)
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The Pancreas
• Functions
– Acini: digestive enzymes
– Islets of Langerhans: insulin and glucagon
• Divisions
– Head, body, tail
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The Pancreas (cont’d.)
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The Liver
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The Liver
• Functions
– Produces heparin, prothrombin, thrombin
– Phagocytosis of bacteria and old blood cells
– Stores excess carbohydrates, minerals, and
vitamins
– Converts toxins into less harmful substances
– Produces bile salts
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The Gallbladder
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Pear-shaped sac
Located in depression on surface of liver
Stores and concentrates bile until needed
Enters duodenum through common bile
duct
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The Small Intestine
• Function: absorption of digested food
• Divisions
– Duodenum: 10 inches
– Jejunum: 8 feet
– Ileum: 12 feet
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The Small Intestine (cont’d.)
• Crypts of Lieberkuhn: secrete digestive
enzymes
• Brunner’s glands: secrete alkaline mucus
• Chyme: digested contents of small
intestine
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The Small Intestine (cont’d.)
• Plicae: folds in the small intestine
• Villi: site of nutrient absorption
– Each villus is covered by microvilli
– Microvilli increase absorption area
– Villus contains arteriole, venule, capillary
network, and lacteal
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The Small Intestine (cont’d.)
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The Large Intestine
• Reabsorption of water
• Manufacture and absorption of vitamins
• Formation and expulsion of feces
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The Large Intestine (cont’d.)
• Cecum: pouchlike area
• Colon: ascending, transverse, descending
– Pouches called haustrae
• Rectum: terminates at the anus
• Anus: controlled by internal and external
sphincter
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The Large Intestine (cont’d.)
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The Large Intestine (cont’d.)
• Mechanical movements
– Haustral churning
– Peristalsis: 3 to 12 contractions per minute
– Mass peristalsis
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The Formation of the Feces
• Feces: semisolid mass originating from
chyme
– Contain water, inorganic salts, epithelial cells,
Escherichia coli
• Rectal distention initiates defecation reflex
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Summary
• Described the major activities of the
digestive system
• Discussed the major organs that are part
of the digestive system
• Explained the functions of the liver
• Discussed the absorption of nutrients in
the small intestine and the formation of
feces in the large intestine
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