chapter 15 the digestive system. elsevier items and derived items © 2008, 2004 by mosby, inc., an...

Chapter 15Chapter 15The Digestive SystemThe Digestive System

Elsevier items and derived items © 2008, 2004 by Mosby, Inc., an affiliate of Elsevier Inc.

DIGESTIVE SYSTEM DIGESTIVE SYSTEM (FIGURE 15-1)(FIGURE 15-1)

Irregular tube called Irregular tube called alimentary canalalimentary canal or or gastrointestinal (GI) tractgastrointestinal (GI) tract

Food must first be digested, then Food must first be digested, then absorbed, and later metabolizedabsorbed, and later metabolized


WALL OF THE DIGESTIVE TRACT WALL OF THE DIGESTIVE TRACT (FIGURE 15-2)(FIGURE 15-2)

Digestive tract described as tube that extends Digestive tract described as tube that extends from mouth to anusfrom mouth to anus

Wall of the digestive tube is formed by four layers Wall of the digestive tube is formed by four layers of tissue:of tissue: Mucosa—mucous epitheliumMucosa—mucous epithelium Submucosa—connective tissueSubmucosa—connective tissue Muscularis—two layers of smooth muscle Muscularis—two layers of smooth muscle Serosa—serous membrane that covers the outside of Serosa—serous membrane that covers the outside of

abdominal organs; it attaches the digestive tract to the abdominal organs; it attaches the digestive tract to the wall of the abdominopelvic cavity by forming folds called wall of the abdominopelvic cavity by forming folds called mesenteriesmesenteries


MOUTHMOUTH

Roof—formed by hard palate (parts of maxillary and Roof—formed by hard palate (parts of maxillary and palatine bones) and soft palate, an arch-shaped muscle palatine bones) and soft palate, an arch-shaped muscle separating mouth from pharynx; uvula, a downward separating mouth from pharynx; uvula, a downward projection of soft palate (Figure 15-4)projection of soft palate (Figure 15-4)

Floor—formed by tongue and its muscles; papillae, small Floor—formed by tongue and its muscles; papillae, small elevations on mucosa of tongue; taste buds, found in many elevations on mucosa of tongue; taste buds, found in many papillae; lingual frenulum, fold of mucous membrane that papillae; lingual frenulum, fold of mucous membrane that helps anchor tongue to floor of mouth (Figure 15-4)helps anchor tongue to floor of mouth (Figure 15-4)

Typical tooth (Figure 15-5)Typical tooth (Figure 15-5) Three main parts—crown, neck, and rootThree main parts—crown, neck, and root Enamel, which covers the crown, is hardest tissue in bodyEnamel, which covers the crown, is hardest tissue in body


MOUTHMOUTH

Types of teeth—incisors, cuspids, bicuspids, and Types of teeth—incisors, cuspids, bicuspids, and tricuspids tricuspids

Twenty teeth in temporary set; average age for Twenty teeth in temporary set; average age for cutting first tooth about 6 months; set complete at cutting first tooth about 6 months; set complete at about 2 years of ageabout 2 years of age

Thirty-two teeth in permanent set; 6 years about Thirty-two teeth in permanent set; 6 years about average age for starting to cut first permanent average age for starting to cut first permanent tooth; set complete usually between ages of 17 tooth; set complete usually between ages of 17 and 24 years (Figure 15-6)and 24 years (Figure 15-6)


SALIVARY GLANDS SALIVARY GLANDS (FIGURE 15-7)(FIGURE 15-7)

Parotid glands—largest salivary glandsParotid glands—largest salivary glands Submandibular glands—open into mouth Submandibular glands—open into mouth

on either side of frenulumon either side of frenulum Sublingual glands—open into floor of Sublingual glands—open into floor of

mouthmouth


PHARYNXPHARYNX

Subdivided into three anatomical Subdivided into three anatomical components:components: NasopharynxNasopharynx OropharynxOropharynx LaryngopharynxLaryngopharynx


ESOPHAGUSESOPHAGUS

Connects pharynx to stomachConnects pharynx to stomach Dynamic passageway for foodDynamic passageway for food


STOMACH (Figure 15-8)STOMACH (Figure 15-8)

Size—expands after large meal; about size of Size—expands after large meal; about size of large sausage when emptylarge sausage when empty

Food enters stomach through gastroesophageal Food enters stomach through gastroesophageal (cardiac) sphincter(cardiac) sphincter

Pyloric sphincter muscle closes opening between Pyloric sphincter muscle closes opening between pylorus (lower part of stomach) and duodenumpylorus (lower part of stomach) and duodenum

Wall—many smooth muscle fibers; contractions Wall—many smooth muscle fibers; contractions produce churning movements (peristalsis)produce churning movements (peristalsis)

Lining—mucous membrane; many microscopic Lining—mucous membrane; many microscopic glands that secrete gastric juice and hydrochloric glands that secrete gastric juice and hydrochloric acid into stomach; mucous membrane lies in folds acid into stomach; mucous membrane lies in folds (rugae) when stomach is empty (rugae) when stomach is empty


SMALL INTESTINE SMALL INTESTINE (FIGURE 15-9)(FIGURE 15-9)

Size—about 7 meters (20 feet) long but Size—about 7 meters (20 feet) long but only 2 cm or so in diameteronly 2 cm or so in diameter

DivisionsDivisions DuodenumDuodenum JejunumJejunum IleumIleum


SMALL INTESTINESMALL INTESTINE

Wall—contains smooth muscle fibers that Wall—contains smooth muscle fibers that contract to produce peristalsiscontract to produce peristalsis

Lining—mucous membrane; many Lining—mucous membrane; many microscopic glands (intestinal glands) microscopic glands (intestinal glands) secrete intestinal juice; villi (microscopic secrete intestinal juice; villi (microscopic finger-shaped projections from surface of finger-shaped projections from surface of mucosa into intestinal cavity) contain blood mucosa into intestinal cavity) contain blood and lymph capillaries and lymph capillaries


LIVER AND GALLBLADDERLIVER AND GALLBLADDER

Size and location—liver is largest gland; fills upper Size and location—liver is largest gland; fills upper right section of abdominal cavity and extends over right section of abdominal cavity and extends over into left sideinto left side

Liver secretes bileLiver secretes bile Ducts (Figure 15-10)Ducts (Figure 15-10)

Hepatic—drains bile from liverHepatic—drains bile from liver Cystic—duct by which bile enters and leaves gallbladderCystic—duct by which bile enters and leaves gallbladder Common bile—formed by union of hepatic and cystic Common bile—formed by union of hepatic and cystic

ducts; drains bile from hepatic or cystic ducts into ducts; drains bile from hepatic or cystic ducts into duodenumduodenum

GallbladderGallbladder Location—undersurface of the liverLocation—undersurface of the liver Function—concentrates and stores bile produced in the Function—concentrates and stores bile produced in the

liver liver


PANCREASPANCREAS

Exocrine gland that lies behind stomachExocrine gland that lies behind stomach FunctionsFunctions

Pancreatic cells secrete pancreatic juice (most Pancreatic cells secrete pancreatic juice (most important digestive juice) into pancreatic ducts; important digestive juice) into pancreatic ducts; main duct empties into duodenummain duct empties into duodenum

Pancreatic islets (of Langerhans)—cells not Pancreatic islets (of Langerhans)—cells not connected with pancreatic ducts; secrete connected with pancreatic ducts; secrete hormones glucagon and insulin into the bloodhormones glucagon and insulin into the blood


LARGE INTESTINE LARGE INTESTINE (FIGURE 15-12)(FIGURE 15-12)

DivisionsDivisions CecumCecum Colon—ascending, transverse, descending, and sigmoidColon—ascending, transverse, descending, and sigmoid RectumRectum

Food enters through ileocecal valve; external Food enters through ileocecal valve; external opening called anusopening called anus

Wall—contains smooth muscle fibers that contract Wall—contains smooth muscle fibers that contract to produce churning, peristalsis, and defecation to produce churning, peristalsis, and defecation

Lining—mucous membraneLining—mucous membrane


APPENDIXAPPENDIX

Blind tube off cecumBlind tube off cecum No important digestive functions in No important digestive functions in

humanshumans


PERITONEUM (FIGURE 15-14)PERITONEUM (FIGURE 15-14)

Definitions—peritoneum, serous membrane lining Definitions—peritoneum, serous membrane lining abdominal cavity and covering abdominal organs; parietal abdominal cavity and covering abdominal organs; parietal layer of peritoneum lines abdominal cavity; visceral layer of layer of peritoneum lines abdominal cavity; visceral layer of peritoneum covers abdominal organs; peritoneal space lies peritoneum covers abdominal organs; peritoneal space lies between parietal and visceral layersbetween parietal and visceral layers

Extensions—largest are the mesentery and greater Extensions—largest are the mesentery and greater omentum omentum Mesentery is extension of parietal peritoneum, which attaches Mesentery is extension of parietal peritoneum, which attaches

most of small intestine to posterior abdominal wall most of small intestine to posterior abdominal wall Greater omentum, or “lace apron,” hangs down from lower Greater omentum, or “lace apron,” hangs down from lower

edge of stomach and transverse colon over intestinesedge of stomach and transverse colon over intestines X-ray studies of the GI tract—radiopaque contrast medium X-ray studies of the GI tract—radiopaque contrast medium

used to help visualize structures in study imagesused to help visualize structures in study images


DIGESTION (TABLE 15-2)DIGESTION (TABLE 15-2)

Definition—transforms foods into substances that Definition—transforms foods into substances that can be absorbed and used by cellscan be absorbed and used by cells Mechanical digestion—chewing (mastication), Mechanical digestion—chewing (mastication),

swallowing (deglutition), and peristalsis break food into swallowing (deglutition), and peristalsis break food into tiny particles, mix them well with digestive juices, and tiny particles, mix them well with digestive juices, and move them along the digestive tractmove them along the digestive tract

Chemical digestion—breaks up large food molecules Chemical digestion—breaks up large food molecules into compounds that have smaller molecules; brought into compounds that have smaller molecules; brought about by digestive enzymes (Figure 15-15)about by digestive enzymes (Figure 15-15)

Enzymes and chemical digestionEnzymes and chemical digestion Enzymes are specialized protein molecules that act as Enzymes are specialized protein molecules that act as

catalystscatalysts Breakdown process called hydrolysisBreakdown process called hydrolysis


DIGESTIONDIGESTION

Carbohydrate digestion—mainly in small Carbohydrate digestion—mainly in small intestineintestine Pancreatic amylase—breaks polysaccharides Pancreatic amylase—breaks polysaccharides

down to disaccharidesdown to disaccharides Intestinal juice enzymesIntestinal juice enzymes

• Maltase—changes maltose to glucoseMaltase—changes maltose to glucose

• Sucrase—changes sucrose to glucoseSucrase—changes sucrose to glucose

• Lactase—changes lactose to glucoseLactase—changes lactose to glucose


DIGESTIONDIGESTION

Protein digestion—starts in stomach; completed in Protein digestion—starts in stomach; completed in small intestinesmall intestine Gastric juice enzymeGastric juice enzyme pepsin pepsin partially digests proteins partially digests proteins Pancreatic enzyme, Pancreatic enzyme, trypsintrypsin, continues digestion of , continues digestion of

proteinsproteins Intestinal enzymes, Intestinal enzymes, peptidasespeptidases, complete digestion of , complete digestion of

partially digested proteins and convert them to amino partially digested proteins and convert them to amino acidsacids

Fat digestionFat digestion Bile contains no enzymes but emulsifies fats (breaks fat Bile contains no enzymes but emulsifies fats (breaks fat

droplets into very small droplets)droplets into very small droplets) Pancreatic lipase changes emulsified fats to fatty acids Pancreatic lipase changes emulsified fats to fatty acids

and glycerol in small intestineand glycerol in small intestine


ABSORPTIONABSORPTION

Definition—process by which digested food Definition—process by which digested food moves from intestine into blood or lymphmoves from intestine into blood or lymph

Foods and most water minerals and vitamins are Foods and most water minerals and vitamins are absorbed from small intestine; some water and absorbed from small intestine; some water and vitamin K also absorbed from large intestinevitamin K also absorbed from large intestine

Surface area absorption Surface area absorption Structural adaptations increase absorptive surface areaStructural adaptations increase absorptive surface area Fractal geometry—study of fragmented geometric Fractal geometry—study of fragmented geometric

irregular shapes such as those in lining of intestineirregular shapes such as those in lining of intestine

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