1. Pharynx and Esophagus Deglutition –Moves a bolus from the mouth to the stomach Mouth Fauces Oropharynx –Second division of the pharynx Esophagus –Pierces diaphragm –First segment of digestive tube proper –Normally flattened –Stratified squamous epithelium –Striated, mixed, and smooth muscle Stomach

3. Stomach (Figure 25-10) Size and position of the stomach –Digestive tube dilates into an elongated pouchlike structure –Various factors affect size Gender Amount of distension When empty, it is about the size of a large sausage In adults, capacity ranges from 1.0 to 1.5 liters –Located in the upper part of abdominal cavity Under the liver and diaphragm Primarily left of the median line Epigastrium and left hypochondrium (Figure 1-14) Can also crowd the heart and diaphragm after large meals

4. Stomach (Figure 25-10) Divisions of the stomach –Fundus Enlarged portion To the left and above the opening of esophagus into stomach –Body central portion of stomach –Pylorus Lower part of stomach Curves of the stomach –Lesser curvature Upper right curve of stomach –Greater curvature Lower left curve of stomach

5. Stomach (Figure 25-10) Sphincter muscles –Guard both stomach openings –Circular fibers Open when relaxed Closed when contracted –Lower esophageal sphincter (LES) or cardiac sphincter Controls opening of esophagus into stomach –Pyloric sphincter Controls outlet of pyloric portion of stomach into duodenum

7. Stomach Stomach wall –Gastric mucosa Epithelial lining has rugae marked by gastric pits (Figures 25-11 and 25-12) Gastric glands –Found below level of the pits –Secrete most of the gastric juice Chief cells –Secretory cells found in gastric glands –Secrete the enzymes of gastric juice Parietal cells –Secretory cells found in gastric glands –Secrete hydrochloric acid –Thought to produce intrinsic factor needed for vitamin B12 absorption Endocrine cells –Secrete gastrin and ghrelin –Gastric muscularis Thick layer of muscle with three distinct sublayers

9. Stomach Functions of the stomach –Reservoir for food Once partially digested, food moves further along GI tract –Secretes gastric juice Acids and enzymes aid in digestion of food –Breaks food into small particles and mixes them with gastric juice Contractions of the muscular coat –Secretes intrinsic factor –Limited absorption Certain drugs, water, alcohol, short-chain fatty acids –Produces gastrin Regulates digestive functions –Helps protect body from pathogenic bacteria

10. Small Intestine Size and position of the small intestine –2.5 cm in diameter –6 m in length –Coiled loops fill most of abdominal cavity Divisions of the small intestine –Duodenum Uppermost division Approximately 25 cm long Shaped roughly like the letter C –Jejunum Approximately 2.5 m long –Ileum Approximately 3.5 m long

11. Small Intestine Wall of the small intestine (Figure 25-14) –Intestinal lining has plicae (folds) with villi (projections) –Villi—important modifications of mucosal layer Each villus contains an arteriole, venule, and lacteal Covered by a brush border made up of 1,700 ultrafine microvilli per cell Villi and microvilli increase surface area of small intestine hundreds of times –Main site of digestion and absorption –Mucus-secreting goblet cells –Intestinal crypts are areas of rapid mitotic divisions –Enzymes inhibit bacterial growth

13. Large Intestine Size of the large intestine –Average diameter, 6 cm –Approximately 1.5 to 1.8 m long

15. Large Intestine Divisions of the large intestine (Figure 25-16) –Cecum First 5 to 8 cm of large intestine Blind pouch located in lower right quadrant of abdomen –Colon Ascending colon –Vertical position on right side of abdomen –Ileocecal valve prevents material passing from large intestine into ileum Transverse colon –Passes horizontally across abdomen –Above small intestine –Extends from hepatic flexure to splenic flexure Descending colon –Vertical position on left side of abdomen Sigmoid colon joins descending colon to rectum Rectum –Last 7 or 8 inches of intestinal tube –Terminal inch is anal canal with opening called the anus (Fig 25-17)

16. Large Intestine Wall of the large intestine (Figure 25-19) –Intestinal mucous glands Produce lubricating mucus Coats feces as they are formed –Uneven distribution of fibers in the muscle coat