Chapter 15 The Digestive System

Chapter 15The Digestive System

Copyright © 2005 Mosby, Inc. All rights reserved. 2Elsevier items and derived items © 2008, 2004 by Mosby, Inc., an affiliate of Elsevier Inc.

DIGESTIVE SYSTEM (FIGURE 15-1)

Irregular tube called alimentary canal or gastrointestinal (GI) tract

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

Slide 2


Slide 3


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

Slide 4


Slide 5


MOUTHRoof—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

Slide 6


Slide 7


Slide 8


Slide 9


Slide 10


MOUTHTypes 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)

Slide 11


Slide 12


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

Slide 13


Slide 14


PHARYNX

Subdivided into three anatomical components: Nasopharynx Oropharynx Laryngopharynx

Slide 15


ESOPHAGUS

Connects pharynx to stomach

Dynamic passageway for food

Slide 16


STOMACH (Figure 15-8)Size—expands after large meal; about size of large sausage when emptyFood enters stomach through gastroesophageal (cardiac) sphincterPyloric sphincter muscle closes opening between pylorus (lower part of stomach) and duodenumWall—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

Slide 17


Slide 18


SMALL INTESTINE (FIGURE 15-9)

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

Divisions Duodenum Jejunum Ileum

Slide 19


Slide 20


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

Slide 21


LIVER AND GALLBLADDERSize and location—liver is largest gland; fills upper right section of abdominal cavity and extends over into left sideLiver secretes bileDucts (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

Slide 22


Slide 23


PANCREASExocrine 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

Slide 24


LARGE INTESTINE (FIGURE 15-12)Divisions Cecum Colon—ascending, transverse, descending, and sigmoid Rectum

Food enters through ileocecal valve; external opening called anusWall—contains smooth muscle fibers that contract to produce churning, peristalsis, and defecation Lining—mucous membrane

Slide 25


Slide 26


APPENDIX

Blind tube off cecum

No important digestive functions in humans

Slide 27


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 layersExtensions—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 intestinesX-ray studies of the GI tract—radiopaque contrast medium used to help visualize structures in study images

Slide 28


Slide 29


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

Slide 30


Slide 31


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

Slide 32


DIGESTIONProtein 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

Slide 33


ABSORPTIONDefinition—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

Slide 34

Documents

Chapter 15 The Digestive System