Chapter 15 The Digestive System Mosby items and

OVERVIEW OF THE DIGESTIVE SYSTEM (Figure 15 -1 and Table 15 -1) � Irregular tube called alimentary canal or gastrointestinal (GI) tract and accessory organs of digestion � Food must first be digested, and absorbed Mosby items and derived items © 2012 by Mosby, Inc. , an affiliate of Elsevier Inc. Slide 2

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PRIMARY MECHANISMS OF THE DIGESTIVE SYSTEM (Table 15 -2) Ingestion—complex foods taken into the GI tract Digestion—group of processes that break complex nutrients into simpler ones Mechanical digestion— digestion breakup of large chunks of food into smaller bits Ø Chemical digestion— digestion breaks large molecules into smaller ones Ø Motility—a number of GI movements resulting from muscular contraction Secretion—release of digestive juices and hormones that facilitate digestion Absorption—movement of digested nutrients into the internal environment of the body Regulation—neural, hormonal and other mechanisms that regulate digestive activity Mosby items and derived items © 2012 by Mosby, Inc. , an affiliate of Elsevier Inc. Slide 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—type varies depending on GI location (tough and stratified or delicate and simple epithelium); mucus production • Submucosa—connective tissue layer • Muscularis—circular, longitudinal, and oblique (in stomach) layers of muscle important in GI motility �Peristalsis—“wavelike” movement pushes food down the tract (Figure 15 -3) �Segmentation—“back-and-forth” movement (Figure 15 -4) • 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 Mosby items and derived items © 2012 by Mosby, Inc. , an affiliate of Elsevier Inc. Slide 7

MOUTH � � � Roof—formed by hard palate (parts of maxillary and palatine bones) and soft palate, an archshaped muscle separating mouth from pharynx; uvula, a downward projection of soft palate (Figure 15 -5) 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 -5) Typical tooth (Figure 15 -6) • Three main parts—crown, neck, and root • Enamel, which covers the crown, is hardest tissue in body Mosby items and derived items © 2012 by Mosby, Inc. , an affiliate of Elsevier Inc. Slide 11

MOUTH (cont. ) Types of teeth—incisors, cuspids, bicuspids, and tricuspids � Twenty teeth in deciduous or baby set; average for cutting first tooth about 6 months; set complete at about 30 months of age � Thirty-two teeth in permanent set; 6 years about average for starting to cut first permanent tooth; set complete usually between ages of 17 and 24 years (Figure 15 -5) � Mosby items and derived items © 2012 by Mosby, Inc. , an affiliate of Elsevier Inc. Slide 14

SALIVARY GLANDS (Figure 15 -7) � Saliva—exocrine ducts gland secretion flows into • Serous type—watery and contains enzymes (salivary amylase) but no mucus �Produced by serous-type secretory cells (Figure 15 -7, B) • Mucus type—thick, slippery and contains mucus but no enzymes �Lubricates food during mastication �Produced by mucus-type secretory cells (Figure 15 -7, B) � Parotid glands (Figure 15 -7) • Largest salivary glands • Produces serous type saliva • Mumps—infection of parotids Mosby items and derived items © 2012 by Mosby, Inc. , an affiliate of Elsevier Inc. Slide 15

SALIVARY GLANDS (Figure 15 -7) (cont. ) � Submandibular glands—(Figure 15 -7) • Mixed gland—produces both serous-type and mucus-type saliva (Figure 15 -7, B) • Located below mandibular angle • Ducts open on either side of lingual frenulum � Sublingual glands—(Figure 15 -7) • Produce only mucus-type saliva • Multiple ducts open into floor of mouth Mosby items and derived items © 2012 by Mosby, Inc. , an affiliate of Elsevier Inc. Slide 17

PHARYNX � Anatomic components: nasopharynx, oropharynx, laryngopharynx (see anatomic description in Chapter 4 and Figure 14 -4) � Oropharynx most involved segment in digestive process of swallowing or deglutition • Regulation of deglutition movements via motor cortex of cerebrum (voluntary) and “deglutition center” of brainstem (involuntary) Mosby items and derived items © 2012 by Mosby, Inc. , an affiliate of Elsevier Inc. Slide 18

ESOPHAGUS � Connects pharynx to stomach � Dynamic passageway for food � Food enters stomach by passing through lower esophageal sphincter (LES) or cardiac sphincter Mosby items and derived items © 2012 by Mosby, Inc. , an affiliate of Elsevier Inc. Slide 19

STOMACH (Figure 15 -8) Size—expands after large meal; about size of large sausage when empty � Food enters stomach through (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 � Mosby items and derived items © 2012 by Mosby, Inc. , an affiliate of Elsevier Inc. Slide 20

SMALL INTESTINE (Figure 15 -9) � Size—about 7 meters (20 feet) long but only 2 cm or so in diameter � Divisions • Duodenum • Jejunum • Ileum Mosby items and derived items © 2012 by Mosby, Inc. , an affiliate of Elsevier Inc. Slide 22

SMALL INTESTINE (cont. ) � Wall—contains smooth muscle fibers that contract to produce peristalsis and segmentation movements � 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 Mosby items and derived items © 2012 by Mosby, Inc. , an affiliate of Elsevier Inc. Slide 24

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 Mosby items and derived items © 2012 by Mosby, Inc. , an affiliate of Elsevier Inc. Slide 25

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 Mosby items and derived items © 2012 by Mosby, Inc. , an affiliate of Elsevier Inc. Slide 27

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 Mosby items and derived items © 2012 by Mosby, Inc. , an affiliate of Elsevier Inc. Slide 28

APPENDIX � Blind tube off cecum � No important digestive functions in humans Mosby

PERITONEUM (Figure 15 -14) � Definitions—peritoneum, continuous 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 Mosby items and derived items © 2012 by Mosby, Inc. , an affiliate of Elsevier Inc. Slide 31

DIGESTION (Table 15 -3) � 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 Mosby items and derived items © 2012 by Mosby, Inc. , an affiliate of Elsevier Inc. Slide 33

DIGESTION (cont. ) � 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 Mosby items and derived items © 2012 by Mosby, Inc. , an affiliate of Elsevier Inc. Slide 36

DIGESTION (cont. ) � 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 Mosby items and derived items © 2012 by Mosby, Inc. , an affiliate of Elsevier Inc. Slide 37

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 Mosby items and derived items © 2012 by Mosby, Inc. , an affiliate of Elsevier Inc. Slide 38