Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 1 Chapter 25 Anatomy of the Digestive System

Mosby items and derived items © 2007, 2003 by Mosby, Inc. Slide 1

Chapter 25Chapter 25Anatomy of the Digestive SystemAnatomy of the Digestive System


Overview of the Digestive System Overview of the Digestive System

Role of the digestive systemRole of the digestive system

Prepares food for absorption and use by all the Prepares food for absorption and use by all the cells of the bodycells of the body

Food material not absorbed becomes feces that is Food material not absorbed becomes feces that is eliminatedeliminated

Digestion depends on both endocrine and Digestion depends on both endocrine and exocrine secretions and the controlled movement exocrine secretions and the controlled movement of ingested food materials through the of ingested food materials through the gastrointestinal (GI) tractgastrointestinal (GI) tract



Overview of the Digestive SystemOverview of the Digestive System

Organization of the digestive systemOrganization of the digestive system

Organs of digestionOrgans of digestion

• Main organs of the digestive system form the GI tract that Main organs of the digestive system form the GI tract that extends through the abdominopelvic cavityextends through the abdominopelvic cavity

• Ingested food material passing through the lumen of the GI Ingested food material passing through the lumen of the GI tract is outside the internal environment of the bodytract is outside the internal environment of the body

Wall of the GI tractWall of the GI tract

• Layers—GI tract is made of four layers of tissues: mucosa, Layers—GI tract is made of four layers of tissues: mucosa, submucosa, muscularis, and serosasubmucosa, muscularis, and serosa

• Modifications of layers—layers of the GI tract have various Modifications of layers—layers of the GI tract have various modifications to enable it to perform various functionsmodifications to enable it to perform various functions


MouthMouth

Structure of the oral cavity (buccal cavity)Structure of the oral cavity (buccal cavity)

Lips—covered externally by skin and internally by Lips—covered externally by skin and internally by mucous membrane; junction between skin and mucous membrane; junction between skin and mucous membrane is highly sensitive; when lips mucous membrane is highly sensitive; when lips are closed, line of contact is oral fissureare closed, line of contact is oral fissure

Cheeks—lateral boundaries of oral cavity, Cheeks—lateral boundaries of oral cavity, continuous with lips and lined by mucous continuous with lips and lined by mucous membrane; formed in large part by buccinator membrane; formed in large part by buccinator muscle covered by adipose tissue; contain muscle covered by adipose tissue; contain mucus-secreting glandsmucus-secreting glands


MouthMouth Structure of the oral cavity (buccal cavity) (cont.)Structure of the oral cavity (buccal cavity) (cont.)

Hard and soft palatesHard and soft palates

• Hard palate consists of portions of four bones: two maxillae and two Hard palate consists of portions of four bones: two maxillae and two palatinespalatines

• Soft palate forms partition between the mouth and the nasopharynx Soft palate forms partition between the mouth and the nasopharynx and is made of muscle arranged in an archand is made of muscle arranged in an arch

• Suspended from midpoint of posterior border of the arch is the uvulaSuspended from midpoint of posterior border of the arch is the uvula

Tongue—solid mass of skeletal muscle covered by a mucous Tongue—solid mass of skeletal muscle covered by a mucous membrane; extremely maneuverable (Figure 25-4)membrane; extremely maneuverable (Figure 25-4)

• Important for mastication and deglutitionImportant for mastication and deglutition

• Has three parts: root, tip, and bodyHas three parts: root, tip, and body

• Papillae located on dorsal surface of tonguePapillae located on dorsal surface of tongue

• Lingual frenulum anchors tongue to floor of mouthLingual frenulum anchors tongue to floor of mouth


MouthMouth

Salivary glands—three pairs of compound tubuloalveolar Salivary glands—three pairs of compound tubuloalveolar glands secrete approximately 1 liter of saliva each day; glands secrete approximately 1 liter of saliva each day; buccal glands contribute less than 5% buccal glands contribute less than 5% of total salivary volume but provide for hygiene and of total salivary volume but provide for hygiene and comfort of oral tissuescomfort of oral tissues

Parotid glands—largest of the paired salivary glands; produce Parotid glands—largest of the paired salivary glands; produce watery saliva containing enzymeswatery saliva containing enzymes

Submandibular glands—compound glands that contain enzyme Submandibular glands—compound glands that contain enzyme and mucus-producing elementsand mucus-producing elements

Sublingual glands—smallest of the salivary glands; produce a Sublingual glands—smallest of the salivary glands; produce a mucous type of salivamucous type of saliva


MouthMouth

Teeth—organs of masticationTeeth—organs of mastication

Typical toothTypical tooth

• Crown—exposed portion of a tooth, covered by enamel; ideally Crown—exposed portion of a tooth, covered by enamel; ideally suited to withstand abrasion during masticationsuited to withstand abrasion during mastication

• Neck—narrow portion that joins the crown to the root; surrounded Neck—narrow portion that joins the crown to the root; surrounded by the gingivaeby the gingivae

• Root fits into socket of alveolar process and is suspended by Root fits into socket of alveolar process and is suspended by fibrous periodontal membranefibrous periodontal membrane

• Outer shell contains two additional tissues: dentin and cementumOuter shell contains two additional tissues: dentin and cementum

Dentin makes up the greatest portion of the tooth shell; at crown, Dentin makes up the greatest portion of the tooth shell; at crown, covered by enamel, and at neck and root, covered by cementumcovered by enamel, and at neck and root, covered by cementum

Pulp cavity—located in dentin, contains connective tissue, blood, Pulp cavity—located in dentin, contains connective tissue, blood, and lymphatic vessels and sensory nervesand lymphatic vessels and sensory nerves



MouthMouth

Teeth (cont.)Teeth (cont.)

Types of teethTypes of teeth

• Deciduous teeth—20 baby teeth, which appear early in lifeDeciduous teeth—20 baby teeth, which appear early in life

• Permanent teeth—32 teeth, which replace the deciduous teethPermanent teeth—32 teeth, which replace the deciduous teeth



PharynxPharynx

Tube through which a bolus passes when Tube through which a bolus passes when moved from the mouth to the esophagus by moved from the mouth to the esophagus by the process of deglutitionthe process of deglutition



Esophagus Esophagus

Tube that extends from the pharynx to Tube that extends from the pharynx to the stomachthe stomach

First segment of digestive tubeFirst segment of digestive tube



StomachStomach

Size and position of the stomachSize and position of the stomach

Size varies according to factors such as gender and amount of Size varies according to factors such as gender and amount of distentiondistention

• When no food is in stomach, it is about the size of a large sausageWhen no food is in stomach, it is about the size of a large sausage

• In adults, capacity ranges from 1.0 to 1.5 litersIn adults, capacity ranges from 1.0 to 1.5 liters

Stomach location: upper part of abdominal cavity under liver and Stomach location: upper part of abdominal cavity under liver and diaphragmdiaphragm

Divisions of the stomachDivisions of the stomach

Fundus—enlarged portion to the left and above opening of Fundus—enlarged portion to the left and above opening of esophagus into stomachesophagus into stomach

Body—central portion of stomachBody—central portion of stomach

Pylorus—lower part of stomachPylorus—lower part of stomach



StomachStomach

Curves of the stomachCurves of the stomach

Lesser curvature—upper right curve of stomachLesser curvature—upper right curve of stomach

Greater curvature—lower left curve of stomachGreater curvature—lower left curve of stomach

Sphincter muscles—circular fibers arranged so that Sphincter muscles—circular fibers arranged so that there is an opening in the center when relaxed and there is an opening in the center when relaxed and no opening when contractedno opening when contracted

Lower esophageal sphincter (LES) or cardiac sphincter Lower esophageal sphincter (LES) or cardiac sphincter controls opening of esophagus into stomachcontrols opening of esophagus into stomach

Pyloric sphincter controls outlet of pyloric portion of stomach Pyloric sphincter controls outlet of pyloric portion of stomach into duodenuminto duodenum


StomachStomach Stomach wallStomach wall

Gastric mucosaGastric mucosa• Epithelial lining has rugae marked by gastric pits Epithelial lining has rugae marked by gastric pits

Gastric glands—found below level of the pits; secrete most Gastric glands—found below level of the pits; secrete most of gastric juiceof gastric juice

• Chief cells—secretory cells found in gastric glands; secrete the Chief cells—secretory cells found in gastric glands; secrete the enzymes of gastric juiceenzymes of gastric juice

• Parietal cells—secretory cells found in gastric glands; secrete Parietal cells—secretory cells found in gastric glands; secrete hydrochloric acid; thought to produce intrinsic factor needed for vitamin hydrochloric acid; thought to produce intrinsic factor needed for vitamin B12 absorptionB12 absorption

• Endocrine cells—secrete gastrin and ghrelinEndocrine cells—secrete gastrin and ghrelin Gastric muscularis—thick layer of muscle with three distinct Gastric muscularis—thick layer of muscle with three distinct

sublayers of smooth muscle tissue arranged in a crisscrossing sublayers of smooth muscle tissue arranged in a crisscrossing pattern; this pattern allows stomach to contract strongly at pattern; this pattern allows stomach to contract strongly at many anglesmany angles


StomachStomach Functions of the stomachFunctions of the stomach

Reservoir for food until it is partially digested and Reservoir for food until it is partially digested and moved further along GI tractmoved further along GI tract

Secretes gastric juice to aid in digestion of foodSecretes gastric juice to aid in digestion of food Breaks food into small particles and mixes them Breaks food into small particles and mixes them

with gastric juicewith gastric juice Secretes intrinsic factorSecretes intrinsic factor Limited absorptionLimited absorption Produces gastrin and ghrelinProduces gastrin and ghrelin Helps protect body from pathogenic bacteria Helps protect body from pathogenic bacteria

swallowed with foodswallowed with food


Small IntestineSmall Intestine

Size and position of the small intestine—tube Size and position of the small intestine—tube approximately 2.5 cm in diameter and 6 m in approximately 2.5 cm in diameter and 6 m in length; coiled loops fill most of abdominal length; coiled loops fill most of abdominal cavitycavity

Divisions of the small intestineDivisions of the small intestine

Duodenum—uppermost division; approximately Duodenum—uppermost division; approximately 25 cm long, shaped roughly like the letter C25 cm long, shaped roughly like the letter C

Jejunum—approximately 2.5 m longJejunum—approximately 2.5 m long

Ileum—approximately 3.5 m longIleum—approximately 3.5 m long



Small IntestineSmall Intestine

Wall of the small intestineWall of the small intestine

Intestinal lining has plicae with villiIntestinal lining has plicae with villi

Villi—important modifications of mucosal layerVilli—important modifications of mucosal layer

• Each villus contains an arteriole, venule, and lactealEach villus contains an arteriole, venule, and lacteal

• Covered by a brush border made up of 1,700 ultrafine Covered by a brush border made up of 1,700 ultrafine microvilli per cellmicrovilli per cell

• Villi and microvilli increase surface area of small intestine Villi and microvilli increase surface area of small intestine hundreds of timeshundreds of times



Large IntestineLarge Intestine Size of the large intestine—average diameter, 6 cm; Size of the large intestine—average diameter, 6 cm;

length, approximately 1.5 to 1.8 mlength, approximately 1.5 to 1.8 m Divisions of the large intestineDivisions of the large intestine

Cecum—first 5 to 8 cm of large intestine, blind pouch located in Cecum—first 5 to 8 cm of large intestine, blind pouch located in lower right quadrant of abdomenlower right quadrant of abdomen

ColonColon• Ascending colon—vertical position on right side of abdomen; Ascending colon—vertical position on right side of abdomen;

ileocecal valve prevents material passing from large intestine into ileocecal valve prevents material passing from large intestine into ileumileum

• Transverse colon passes horizontally across abdomen, above small Transverse colon passes horizontally across abdomen, above small intestine; extends from hepatic flexure to splenic flexureintestine; extends from hepatic flexure to splenic flexure

• Descending colon—vertical position on left side of abdomenDescending colon—vertical position on left side of abdomen

• Sigmoid colon joins descending colon to rectumSigmoid colon joins descending colon to rectum

• Rectum—last 7 or 8 inches of intestinal tube; terminal inch is anal Rectum—last 7 or 8 inches of intestinal tube; terminal inch is anal canal with opening called the anus (Figure 25-17)canal with opening called the anus (Figure 25-17)



Large IntestineLarge Intestine

Wall of the large intestine (Figure 25-19)Wall of the large intestine (Figure 25-19)

Intestinal mucous glands produce lubricating Intestinal mucous glands produce lubricating mucus that coats feces as they are formedmucus that coats feces as they are formed

Uneven distribution of fibers in the muscle coatUneven distribution of fibers in the muscle coat


Vermiform Appendix Vermiform Appendix

Accessory organ of digestive system; 8 to 10 Accessory organ of digestive system; 8 to 10 cm in length; communicates with cecumcm in length; communicates with cecum


Peritoneum Peritoneum

Large, continuous sheet of serous membraneLarge, continuous sheet of serous membrane

Made up of parietal and visceral layersMade up of parietal and visceral layers

Mesentery—projection of parietal peritoneum; Mesentery—projection of parietal peritoneum; allows free movement of each coil of the allows free movement of each coil of the intestine and helps prevent strangulation of intestine and helps prevent strangulation of the long tubethe long tube

Transverse mesocolon—extension of Transverse mesocolon—extension of peritoneum that supports transverse colonperitoneum that supports transverse colon


LiverLiver

Location and size of the liver—largest gland in body, Location and size of the liver—largest gland in body, weighs approximately 1.5 kg; lies under diaphragm; weighs approximately 1.5 kg; lies under diaphragm; occupies most of right hypochondrium and part of occupies most of right hypochondrium and part of epigastriumepigastrium

Liver lobes and lobules—two lobes separated by Liver lobes and lobules—two lobes separated by falciform ligamentfalciform ligament

Left lobe—forms about one sixth of liverLeft lobe—forms about one sixth of liver

Right lobe—forms about five sixths of liver; divides into right Right lobe—forms about five sixths of liver; divides into right lobe proper, caudate lobe, and quadrate lobelobe proper, caudate lobe, and quadrate lobe

Hepatic lobules—anatomical units of liver; small branch of Hepatic lobules—anatomical units of liver; small branch of hepatic vein extends through the center of each lobulehepatic vein extends through the center of each lobule



LiverLiver

Bile ductsBile ducts

Small bile ducts form right and left hepatic ductsSmall bile ducts form right and left hepatic ducts

Right and left hepatic ducts immediately join to Right and left hepatic ducts immediately join to form one hepatic ductform one hepatic duct

Hepatic duct merges with cystic duct to form Hepatic duct merges with cystic duct to form common bile duct, which opens into duodenumcommon bile duct, which opens into duodenum


LiverLiver

Functions of the liverFunctions of the liver

Detoxification by liver cells—ingested toxic substances and Detoxification by liver cells—ingested toxic substances and toxic substances formed in intestines may be changed to toxic substances formed in intestines may be changed to nontoxic substancesnontoxic substances

Bile secretion by liver—bile salts are formed in liver from Bile secretion by liver—bile salts are formed in liver from cholesterol and are the most essential part of bile; liver cells cholesterol and are the most essential part of bile; liver cells secrete approximately 1 pint of bile per daysecrete approximately 1 pint of bile per day

Liver metabolism carries out numerous important steps in the Liver metabolism carries out numerous important steps in the metabolizing of proteins, fats, and carbohydratesmetabolizing of proteins, fats, and carbohydrates

Storage of substances such as iron and some vitaminsStorage of substances such as iron and some vitamins

Production of important plasma proteinsProduction of important plasma proteins


GallbladderGallbladder

Size and location of the gallbladder—pear-shaped sac Size and location of the gallbladder—pear-shaped sac from 7 to 10 cm long and 3 cm wide at its broadest point; from 7 to 10 cm long and 3 cm wide at its broadest point; holds 30 to 50 ml of bile; lies on undersurface of liverholds 30 to 50 ml of bile; lies on undersurface of liver

Structure of gallbladder—serous, muscular, and mucous Structure of gallbladder—serous, muscular, and mucous layers compose the gallbladder wall; mucosal lining has layers compose the gallbladder wall; mucosal lining has rugaerugae

Functions of gallbladder:Functions of gallbladder:

Storage of bileStorage of bile

Concentration of bile fivefold to tenfoldConcentration of bile fivefold to tenfold

Ejection of the concentrated bile into duodenumEjection of the concentrated bile into duodenum


Pancreas Pancreas

Size and location of the pancreas—grayish pink–colored Size and location of the pancreas—grayish pink–colored gland; 12 to 15 cm long; weighs approximately 60 g; runs gland; 12 to 15 cm long; weighs approximately 60 g; runs from duodenum and behind stomach to spleenfrom duodenum and behind stomach to spleen

Structure of the pancreas—composed of endocrine and Structure of the pancreas—composed of endocrine and exocrine glandular tissueexocrine glandular tissue

Exocrine portion makes up majority of pancreas; has a Exocrine portion makes up majority of pancreas; has a compound acinar arrangement; tiny ducts unite to form main compound acinar arrangement; tiny ducts unite to form main pancreatic duct, which empties into duodenumpancreatic duct, which empties into duodenum

Endocrine portion—embedded between exocrine units; called Endocrine portion—embedded between exocrine units; called pancreatic islets; constitute only 2% of total mass of pancreas; pancreatic islets; constitute only 2% of total mass of pancreas; made up of alpha cells and beta cells; pass secretions into made up of alpha cells and beta cells; pass secretions into capillariescapillaries


PancreasPancreas

Functions of the pancreasFunctions of the pancreas

Acinar units secrete digestive enzymesAcinar units secrete digestive enzymes

Beta cells secrete insulinBeta cells secrete insulin

Alpha cells secrete glucagonAlpha cells secrete glucagon


Cycle of Life: Digestive SystemCycle of Life: Digestive System

Changes in digestive function and structure are age-relatedChanges in digestive function and structure are age-related

Result in diseases or pathological conditionsResult in diseases or pathological conditions

May occur in any segment of intestinal tractMay occur in any segment of intestinal tract

Changes involve accessory organs: teeth, salivary glands, liver, Changes involve accessory organs: teeth, salivary glands, liver, gallbladder, and pancreasgallbladder, and pancreas

Infants—immature intestinal mucosa; intact proteins can Infants—immature intestinal mucosa; intact proteins can pass through epithelial cells lining the tract and trigger pass through epithelial cells lining the tract and trigger allergic responseallergic response

Lactose intolerance affects infants who lack the enzyme Lactose intolerance affects infants who lack the enzyme lactaselactase


Cycle of Life: Digestive SystemCycle of Life: Digestive System

Young age—mumps common in children; Young age—mumps common in children; appendicitis more common in adolescents appendicitis more common in adolescents and then decreases with advancing ageand then decreases with advancing age

Middle age—ulcers and gallbladder disease Middle age—ulcers and gallbladder disease commoncommon

Old age—decreased digestive fluids, slowing Old age—decreased digestive fluids, slowing of peristalsis, and reduced physical activity of peristalsis, and reduced physical activity lead to constipation and diverticulosislead to constipation and diverticulosis

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Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 1 Chapter 25 Anatomy of the Digestive System