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2. Chapter 15 The Digestive System

3. DIGESTIVE SYSTEM (FIGURE 15-1)
Irregular tube called alimentary canal or gastrointestinal (GI) tract
Food must first be digested, then absorbed, and later metabolized

5. WALL OF THE DIGESTIVE TRACT (FIGURE 15-2)
Digestive tract described as tube that extends from mouth to anus
Wall of the digestive tube is formed by four layers of tissue:
Mucosa—mucous epithelium
Submucosa—connective tissue
Muscularis—two layers of smooth muscle
Serosa—serous membrane that covers the outside of abdominal organs; it attaches the digestive tract to the wall of the abdominopelvic cavity by forming folds called mesenteries

7. MOUTH
Roof—formed by hard palate (parts of maxillary and palatine bones) and soft palate, an arch-shaped muscle separating mouth from pharynx; uvula, a downward projection of soft palate (Figure 15-4)
Floor—formed by tongue and its muscles; papillae, small elevations on mucosa of tongue; taste buds, found in many papillae; lingual frenulum, fold of mucous membrane that helps anchor tongue to floor of mouth (Figure 15-4)
Typical tooth (Figure 15-5)
Three main parts—crown, neck, and root
Enamel, which covers the crown, is hardest tissue in body

12. MOUTH Types of teeth—incisors, cuspids, bicuspids, and tricuspids
Twenty teeth in temporary set; average age for cutting first tooth about 6 months; set complete at about 2 years of age
Thirty-two teeth in permanent set; 6 years about average age for starting to cut first permanent tooth; set complete usually between ages of 17 and 24 years (Figure 15-6)

14. SALIVARY GLANDS (FIGURE 15-7)
Parotid glands—largest salivary glands
Submandibular glands—open into mouth on either side of frenulum
Sublingual glands—open into floor of mouth

16. PHARYNX Subdivided into three anatomical components: Nasopharynx
Oropharynx
Laryngopharynx

17. ESOPHAGUS
Connects pharynx to stomach
Dynamic passageway for food

18. STOMACH (Figure 15-8)
Size—expands after large meal; about size of large sausage when empty
Food enters stomach through gastroesophageal (cardiac) sphincter
Pyloric sphincter muscle closes opening between pylorus (lower part of stomach) and duodenum
Wall—many smooth muscle fibers; contractions produce churning movements (peristalsis)
Lining—mucous membrane; many microscopic glands that secrete gastric juice and hydrochloric acid into stomach; mucous membrane lies in folds (rugae) when stomach is empty