1. Chapter 15 The Digestive System Jeanelle F. Jimenez RN, BSN, CCRN

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

4. 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
Mucosa: innermost layer
Submucosa:: contains blood vessels, nerves, and connective tissue
Muscularis: layer that generates peristalsis
Serosa: outermost layer

6. 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
Last bullet point

10. 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)

11. 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

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

14. ESOPHAGUS
Connects pharynx to stomach
Dynamic passageway for food

15. 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

17. SMALL INTESTINE (FIGURE 15-9)
Size—about 7 meters (20 feet) long but only 2 cm or so in diameter
Divisions
Duodenum
Jejunum
Ileum

18. *The vili, plicae, and microvilli increase the absorptive surface area of the small intestine.

19. SMALL INTESTINE
Wall—contains smooth muscle fibers that contract to produce peristalsis
Lining—mucous membrane; many microscopic glands (intestinal glands) secrete intestinal juice; villi (microscopic finger-shaped projections from surface of mucosa into intestinal cavity) contain blood and lymph capillaries

20. LIVER AND GALLBLADDER
Size and location—liver is largest gland; fills upper right section of abdominal cavity and extends over into left side
Liver secretes bile
Ducts (Figure 15-10)
Hepatic—drains bile from liver
Cystic—duct by which bile enters and leaves gallbladder
Common bile—formed by union of hepatic and cystic ducts; drains bile from hepatic or cystic ducts into duodenum
Gallbladder
Location—undersurface of the liver
Function—concentrates and stores bile produced in the liver

22. PANCREAS Exocrine gland that lies behind stomach Functions
Pancreatic cells secrete pancreatic juice (most important digestive juice) into pancreatic ducts; main duct empties into duodenum
Pancreatic islets (of Langerhans)—cells not connected with pancreatic ducts; secrete hormones glucagon and insulin into the blood

23. LARGE INTESTINE (FIGURE 15-12)
Divisions
Cecum
Colon—ascending, transverse, descending, and sigmoid
Rectum
Food enters through ileocecal valve; external opening called anus
Wall—contains smooth muscle fibers that contract to produce churning, peristalsis, and defecation
Lining—mucous membrane

25. APPENDIX Blind tube off cecum
No important digestive functions in humans

26. PERITONEUM (FIGURE 15-14)
Definitions—peritoneum, serous membrane lining abdominal cavity and covering abdominal organs; parietal layer of peritoneum lines abdominal cavity; visceral layer of peritoneum covers abdominal organs; peritoneal space lies between parietal and visceral layers
Extensions—largest are the mesentery and greater omentum
Mesentery is extension of parietal peritoneum, which attaches most of small intestine to posterior abdominal wall
Greater omentum, or “lace apron,” hangs down from lower edge of stomach and transverse colon over intestines
X-ray studies of the GI tract—radiopaque contrast medium used to help visualize structures in study images

28. DIGESTION (TABLE 15-2)
Definition—transforms foods into substances that can be absorbed and used by cells
Mechanical digestion—chewing (mastication), swallowing (deglutition), and peristalsis break food into tiny particles, mix them well with digestive juices, and move them along the digestive tract
Chemical digestion—breaks up large food molecules into compounds that have smaller molecules; brought about by digestive enzymes (Figure 15-15)
Enzymes and chemical digestion
Enzymes are specialized protein molecules that act as catalysts
Breakdown process called hydrolysis

30. DIGESTION Carbohydrate digestion—mainly in small intestine
Pancreatic amylase—breaks polysaccharides down to disaccharides
Intestinal juice enzymes
Maltase—changes maltose to glucose
Sucrase—changes sucrose to glucose
Lactase—changes lactose to glucose

31. DIGESTION
Protein digestion—starts in stomach; completed in small intestine
Gastric juice enzyme pepsin partially digests proteins
Pancreatic enzyme, trypsin, continues digestion of proteins
Intestinal enzymes, peptidases, complete digestion of partially digested proteins and convert them to amino acids
Fat digestion
Bile contains no enzymes but emulsifies fats (breaks fat droplets into very small droplets)
Pancreatic lipase changes emulsified fats to fatty acids and glycerol in small intestine

32. ABSORPTION
Definition—process by which digested food moves from intestine into blood or lymph
Foods and most water minerals and vitamins are absorbed from small intestine; some water and vitamin K also absorbed from large intestine
Surface area absorption
Structural adaptations increase absorptive surface area
Fractal geometry—study of fragmented geometric irregular shapes such as those in lining of intestine