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Anatomy & Physiology Chapter 28: Anatomy of the Digestive System Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Organization of the Digestive System Organs of digestion (Figure 28-1) Main organs of the digestive system form the GI tract that extends through the abdominopelvic cavity Ingested food material passing through the lumen of the GI tract is outside the internal environment of the body Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 2 Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 3 Organization of the Digestive System Wall of the GI tract (Figure 28-2) Mucosa—innermost layer Submucosa—contains numerous glands, blood vessels, and parasympathetic nerves Muscularis—thick layer of muscle tissue Serosa—outermost layer Modifications of layers—structure of layers varies in different regions throughout length of GI tract (Table 28-1) Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 4 Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 5 Mouth Structure of the oral cavity (buccal cavity) (Figure 28-3) Lips Covered externally by skin and internally by mucous membrane Junction between skin and mucous membrane is highly sensitive Line of contact between closed lips forms the oral fissure Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 6 Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 7 Mouth Structure of the oral cavity (cont) Cheeks Lateral boundaries of the oral cavity, continuous with the lips and lined by mucous membrane Formed in large part by the buccinator muscle covered by adipose tissue Contain mucus-secreting glands Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 8 Mouth Structure of the oral cavity (cont) Hard palate and soft palate Hard palate consists of portions of four bones: two maxillae and two palatines Soft palate forms the partition between the mouth and nasopharynx and is made of muscle arranged in an arch Suspended from the midpoint of the posterior border of the arch is the uvula Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 9 Mouth Structure of the oral cavity (cont) Tongue—solid mass of skeletal muscle covered by a mucous membrane; extremely maneuverable Has three parts: root, tip, and body (Figure 284) Papillae located on the dorsal and lateral surfaces of the tongue (Figure 28-5) Lingual frenulum anchors the tongue to the floor of the mouth (Figure 28-6) Intrinsic muscles important for speech and mastication; extrinsic muscles important for deglutition and speech (Figure 28-7) Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 10 Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 11 Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 12 Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 13 Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 14 Mouth Salivary glands Three main pairs of compound tubuloalveolar glands (Figure 28-8) Secrete approximately 1 liter of saliva each day Additional small buccal glands contribute less than 5% of the total salivary volume but provide for hygiene and comfort of oral tissues Parotid glands—largest of the paired salivary glands; produce watery saliva containing enzymes Submandibular glands—compound glands that contain enzyme- and mucus-producing elements Sublingual glands—smallest of the salivary glands; produce a mucous type of saliva Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 15 Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 16 Mouth Teeth—organs of mastication Typical tooth (Figure 28-9) Crown—exposed portion of a tooth, covered by enamel; ideally suited to withstand abrasion during mastication Neck—narrow portion that joins the crown to the root; surrounded by gingivae Root—fits into the socket of the alveolar process; suspended by a fibrous periodontal membrane Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 17 Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 18 Mouth Typical tooth (cont) • Outer shell contains two additional tissues: dentin and cementum Dentin—greatest portion of the tooth shell; at the crown, covered by enamel, and at the neck and root, covered by cementum Pulp cavity—located in dentin, contains connective tissue, blood, and lymphatic vessels and sensory nerves Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 19 Mouth Teeth—organs of mastication Types of teeth (Figure 28-10) • Deciduous teeth—20 baby teeth, which appear early in life • Permanent teeth—32 teeth, which replace the deciduous teeth Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 20 Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 21 Pharynx Tube through which a food bolus passes when moved from the mouth to the esophagus by the process of deglutition Air passes through all three divisions of the pharynx; only terminal portion involved in digestive system Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 22 Esophagus Tube that extends from the pharynx to the stomach; first segment of the digestive tube (Figure 28-11) Lined with stratified squamous epithelium (Figure 28-12) Each end encircled by muscular sphincters Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 23 Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 24 Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 25 Stomach Size and position of the stomach Size varies according to factors such as gender and amount of distention When no food is in the stomach, it is about the size of a large sausage In adults, its capacity ranges from 1.0 to 1.5 liters Stomach location: upper part of the abdominal cavity under the liver and diaphragm Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 26 Stomach Divisions of the stomach (Figure 28-13) Cardia—collarlike region at junction with esophagus Fundus—enlarged portion to the left and above the opening of the esophagus into the stomach Body—central portion of the stomach Pylorus—lower part of the stomach Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 27 Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 28 Stomach Curves of the stomach Lesser curvature—upper right curve of the stomach Greater curvature—lower left curve of the stomach Sphincter muscles—circular fibers arranged so that there is an opening in the center when relaxed and no opening when contracted Lower esophageal sphincter (LES), or cardiac sphincter, controls the opening of the esophagus into the stomach Pyloric sphincter controls the outlet of the pyloric portion of the stomach into the duodenum Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 29 Stomach Stomach wall (Figure 28-14) Gastric mucosa Epithelial lining has rugae marked by gastric pits (Figure 28-15) Gastric glands—found below the level of the pits; secrete most of the gastric juice Chief cells—secretory cells found in the gastric glands; secrete the enzymes of gastric juice Parietal cells—secretory cells found in the gastric glands; secrete hydrochloric acid; thought to produce intrinsic factor needed for vitamin B12 absorption Endocrine cells—secrete gastrin and ghrelin Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 30 Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 31 Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 32 Stomach Stomach wall (cont) Gastric muscularis Thick layer of muscle with three distinct sublayers of smooth muscle tissue arranged in a crisscrossing pattern This pattern allows the stomach to contract strongly at many angles Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 33 Stomach Functions of the stomach Reservoir for food until it is partially digested and moved further along the GI tract Secretes gastric juice to aid in digestion of food Breaks food into small particles and mixes them with gastric juice Secretes intrinsic factor Performs limited absorption Produces gastrin and ghrelin Helps protect the body from pathogenic bacteria swallowed with food Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 34 Small Intestine Size and position of the small intestine Tube approximately 2.5 cm in diameter and 6 m in length Coiled loops fill most of the abdominal cavity (Figure 28-16) 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 Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 35 Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 36 Small Intestine Wall of the small intestine (Figure 28-17) Intestinal lining has plicae with villi Villi—important modifications of the mucosal layer Each villus contains an arteriole, venule, and lacteal vessel Covered by a brush border made up of 1700 ultrafine microvilli per cell Villi and microvilli increase the surface area of the small intestine hundreds of times Crypts—located between villi; contain stem cells from which other cell types are produced and then migrate upward to cover the villi, where they eventually slough off (Figure 28-18) Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 37 Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 38 Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 39 Large Intestine Size of the large intestine Average diameter, 6 cm Length, approximately 1.5 to 1.8 m Divisions of the large intestine (Figure 28-19) Cecum—first 5 to 8 cm of the large intestine; blind pouch located in the lower right quadrant of the abdomen Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 40 Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 41 Large Intestine Divisions of the large intestine (cont) Colon Ascending colon—vertical position on the right side of the abdomen; the ileocecal valve prevents material from passing from the large intestine into the ileum Transverse colon—passes horizontally across the abdomen, above the small intestine; extends from the hepatic flexure to the splenic flexure Descending colon—vertical position on left side of the abdomen Sigmoid colon joins the descending colon to the rectum Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 42 Large Intestine Divisions of the large intestine (cont) Rectum Last 7 or 8 inches of the intestinal tube Terminal inch is the anal canal with the opening called the anus (Figure 28-20) Wall of the large intestine (Figure 28-21) Intestinal mucous glands produce lubricating mucus that coats feces as they are formed Uneven distribution of fibers in the muscle coat Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 43 Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 44 Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 45 Veriform Appendix Accessory organ of digestive system 8 to 10 cm in length; communicates with the cecum Serves as reservoir for beneficial gut bacteria Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 46 Peritoneum Large, continuous sheet of serous membrane (Figure 28-22) Many organs are covered with visceral peritoneum; parietal peritoneum then lines the wall of the abdominopelvic cavity Extraperitoneal space is outside the parietal layer of the peritoneum; retroperitoneal identifies the extraperitoneal space along the posterior and bottom of the abdominopelvic cavity. Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 47 Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 48 Peritoneum Mesentery—projection of the parietal peritoneum; allows free movement of each coil of the intestine and helps prevent strangulation of the long tube (Figure 28-23) Transverse mesocolon—extension of the peritoneum that supports the transverse colon Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 49 Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 50 Liver Location and size of the liver (Figure 28-24) Largest gland in the body, weighs approximately 1.5 kg Lies under the diaphragm; occupies most of the right hypochondrium and part of the epigastrium Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 51 Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 52 Liver Liver lobes and lobules—two lobes separated by the falciform ligament Left lobe—forms about one sixth of the liver Right lobe—forms about five sixths of the liver; divides into right lobe proper, caudate lobe, and quadrate lobe Hepatic lobules—anatomical units of the liver; a small branch of the hepatic vein extends through the center of each lobule (Figures 28-25 and 28-26) Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 53 Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 54 Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 55 Liver Bile ducts (Figure 28-27) Small bile ducts form right and left hepatic ducts Right and left hepatic ducts immediately join to form one hepatic duct Hepatic duct merges with the cystic duct to form the common bile duct, which opens into the duodenum Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 56 Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 57 Liver Functions of the liver Detoxification by liver cells—ingested toxic substances and toxic substances formed in the intestines may be changed to nontoxic substances Bile secretion by liver—bile salts are formed in the liver from cholesterol and are the most essential part of bile; liver cells secrete approximately 1 pint of bile per day Liver metabolism—carries out numerous important steps in metabolizing proteins, fats, and carbohydrates Storage of substances such as iron and some vitamins Production of important plasma proteins Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 58 Gallbladder Size and location of the gallbladder Pear-shaped sac 7 to 10 cm long and 3 cm wide at its broadest point Lies on the undersurface of the liver (Figure 28-27) Structure of the gallbladder Serous, muscular, and mucous layers compose the gallbladder wall The mucosal lining has rugae that expand to allow storage of bile; holds 30 to 50 ml of bile Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 59 Gallbladder Functions of the gallbladder Storage of bile Concentration of bile fivefold to tenfold Ejection of the concentrated bile into the duodenum Gallstones—often made of cholesterol; can form when bile becomes concentrated (Figure 28-28) Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 60 Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 61 Pancreas Size and location of the pancreas Grayish pink–colored gland; 12 to 15 cm long; weighs approximately 60 grams Runs from the duodenum, behind the stomach, to the spleen Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 62 Pancreas Structure of the pancreas (Figure 28-29)— composed of endocrine and exocrine glandular tissue Exocrine portion makes up the majority of the pancreas; has a compound acinar arrangement; tiny ducts unite to form the main pancreatic duct, which empties into the duodenum Endocrine portion—embedded between exocrine units; called pancreatic islets; constitute only 2% of the total mass of the pancreas; made up of alpha cells and beta cells; pass secretions into capillaries Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 63 Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 64 Pancreas Functions of the pancreas Acinar units secrete digestive enzymes Beta cells secrete insulin Alpha cells secrete glucagon Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 65 Cycle of Life: Digestive System Changes in digestive function and structure are age related Result in diseases or pathological conditions May occur in any segment of the intestinal tract Changes involve accessory organs: teeth, salivary glands, liver, gallbladder, and pancreas Infants have immature intestinal mucosa Intact proteins can pass through epithelial cells lining the tract and trigger an allergic response Lactose intolerance affects infants who lack the enzyme lactase Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 66 Cycle of Life: Digestive System Mumps common in children; appendicitis more common in adolescents and then incidence decreases with advancing age Ulcers and gallbladder disease common in middle age Decreased digestive fluids, slowing of peristalsis, and reduced physical activity lead to constipation and diverticulosis in the elderly Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 67