11

Chapter 25Chapter 25

Lecture OutlineLecture Outline

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22

The Digestive SystemThe Digestive System

General anatomy and digestive processesGeneral anatomy and digestive processes Mouth through esophagusMouth through esophagus StomachStomach Liver, gallbladder and pancreasLiver, gallbladder and pancreas Small intestineSmall intestine Chemical digestion and absorptionChemical digestion and absorption Large intestineLarge intestine

33

Digestive FunctionsDigestive Functions

Ingestion Ingestion intake of foodintake of food

Digestion Digestion breakdown of moleculesbreakdown of molecules

Absorption Absorption uptake nutrients into blood/lymphuptake nutrients into blood/lymph

Defecation Defecation elimination of undigested materialelimination of undigested material

44

Stages of DigestionStages of Digestion

Mechanical digestionMechanical digestion physical breakdown of food into smaller particlesphysical breakdown of food into smaller particles teeth and churning action of stomach and intestinesteeth and churning action of stomach and intestines

Chemical digestionChemical digestion series of hydrolysis reactions that break macromolecules series of hydrolysis reactions that break macromolecules

into their monomersinto their monomers enzymes from saliva, stomach, pancreas and intestinesenzymes from saliva, stomach, pancreas and intestines resultsresults

polysaccharides into monosaccharidespolysaccharides into monosaccharides proteins into amino acidsproteins into amino acids fats into glycerol and fatty acids fats into glycerol and fatty acids

55

Digestive ProcessesDigestive Processes

Motility Motility muscular contractions that break up food, mix muscular contractions that break up food, mix

it with enzymes and move it alongit with enzymes and move it along

Secretion Secretion digestive enzymes and hormonesdigestive enzymes and hormones

Membrane transport Membrane transport absorption of nutrientsabsorption of nutrients

66

Subdivisions of Digestive Subdivisions of Digestive SystemSystem

Digestive tract (GI Digestive tract (GI tract)tract) 30 foot long tube 30 foot long tube

extending from extending from mouth to anusmouth to anus

Accessory organsAccessory organs teeth, tongue, liver, teeth, tongue, liver,

gallbladder, gallbladder, pancreas, salivary pancreas, salivary glands glands

77

Tissue Layers of GI TractTissue Layers of GI Tract MucosaMucosa

epitheliumepithelium lamina proprialamina propria muscularis mucosaemuscularis mucosae

SubmucosaSubmucosa Muscularis externaMuscularis externa

inner circular layerinner circular layer outer longitudinal layerouter longitudinal layer

Adventitia or Serosa Adventitia or Serosa areolar tissue or mesotheliumareolar tissue or mesothelium

88

Tissue Layers of GI TractTissue Layers of GI Tract

99

Relationship to PeritoneumRelationship to Peritoneum

Only duodenum, pancreas and parts of large Only duodenum, pancreas and parts of large intestine are retroperitonealintestine are retroperitoneal

Dorsal mesentery suspends GI tract and forms Dorsal mesentery suspends GI tract and forms serosa (visceral peritoneum) of stomach and serosa (visceral peritoneum) of stomach and intestinesintestines

Ventral mesentery forms lesser and greater Ventral mesentery forms lesser and greater omentumomentum lacy layer of connective tissue that contains lymph lacy layer of connective tissue that contains lymph

nodes, lymphatic vessels, blood vessels nodes, lymphatic vessels, blood vessels

1010

Lesser and Greater OmentumLesser and Greater Omentum

Lesser - attaches stomach to liverLesser - attaches stomach to liver Greater - covers small intestines like an apronGreater - covers small intestines like an apron

1111

Mesentery and MesocolonMesentery and Mesocolon

Mesentery of small intestines holds many blood vesselsMesentery of small intestines holds many blood vessels Mesocolon anchors colon to posterior body wallMesocolon anchors colon to posterior body wall

1212

Regulation of Digestive TractRegulation of Digestive Tract

Neural controlNeural control short myenteric reflexes (swallowing)short myenteric reflexes (swallowing) long vagovagal reflexes (parasympathetic long vagovagal reflexes (parasympathetic

stimulation stimulation of digestive motility and secretion)of digestive motility and secretion)

HormonesHormones messengers diffuse into bloodstream, distant messengers diffuse into bloodstream, distant

targetstargets

Paracrine secretionsParacrine secretions messengers diffuse to nearby target cellsmessengers diffuse to nearby target cells

1313

Mouth or Oral CavityMouth or Oral Cavity

1414

Features of Oral CavityFeatures of Oral Cavity Cheeks and lips Cheeks and lips

keep food between teeth for chewing; essential for keep food between teeth for chewing; essential for speech and suckling in infantsspeech and suckling in infants

vestibule - space between teeth and cheeksvestibule - space between teeth and cheeks lips: cutaneous area versus red area lips: cutaneous area versus red area (vermilion)(vermilion)

Tongue is sensitive, muscular manipulator of Tongue is sensitive, muscular manipulator of foodfood papillae and taste buds on dorsal surfacepapillae and taste buds on dorsal surface lingual glands secrete saliva, tonsils in rootlingual glands secrete saliva, tonsils in root

Hard and soft palateHard and soft palate allow breathing and chewing at same timeallow breathing and chewing at same time palatoglossal and palatopharyngeal archespalatoglossal and palatopharyngeal arches

1515

DentitionDentition

Baby teeth (20) by 2 years; Adult (32) between 6 and 25Baby teeth (20) by 2 years; Adult (32) between 6 and 25 Occlusal surfaces and cusp numbers differOcclusal surfaces and cusp numbers differ

1616

Permanent and Deciduous Permanent and Deciduous TeethTeeth

1717

Periodontal ligament is Periodontal ligament is modified periosteummodified periosteum anchors into alveolusanchors into alveolus

Cementum and dentin are Cementum and dentin are living tissueliving tissue

Enamel is noncellular Enamel is noncellular secretion formed during secretion formed during developmentdevelopment

Root canal leads into pulp Root canal leads into pulp cavitycavity nerves and blood vesselsnerves and blood vessels

Gingiva or gumsGingiva or gums

Tooth StructureTooth Structure

1818

Mastication or ChewingMastication or Chewing

Breaks food into smaller pieces to be Breaks food into smaller pieces to be swallowedswallowed surface area exposed to digestive enzymessurface area exposed to digestive enzymes

Contact of food with sensory receptors Contact of food with sensory receptors triggers chewing reflextriggers chewing reflex tongue, buccinator and orbicularis oris manipulate tongue, buccinator and orbicularis oris manipulate

foodfood masseter and temporalis elevate the teeth to masseter and temporalis elevate the teeth to

crush foodcrush food medial and lateral pterygoids swing teeth in side-medial and lateral pterygoids swing teeth in side-

to-side grinding action of molarsto-side grinding action of molars

1919

SalivaSaliva Functions of salivaFunctions of saliva

moisten, begin starch and fat digestion, cleanse teeth, moisten, begin starch and fat digestion, cleanse teeth, inhibit bacteria, bind food together into bolusinhibit bacteria, bind food together into bolus

Hypotonic solution of 99.5% water and solutesHypotonic solution of 99.5% water and solutes salivary amylase, begins starch digestionsalivary amylase, begins starch digestion lingual lipase, digests fat activated by stomach acidlingual lipase, digests fat activated by stomach acid mucus, aids in swallowingmucus, aids in swallowing lysozyme, enzyme kills bacterialysozyme, enzyme kills bacteria immunoglobulin A, inhibits bacterial growthimmunoglobulin A, inhibits bacterial growth electrolytes = Naelectrolytes = Na++, K, K++, Cl, Cl--, phosphate and bicarbonate, phosphate and bicarbonate

pH of 6.8 to 7.0pH of 6.8 to 7.0

2020

Salivary GlandsSalivary Glands

Small intrinsic glands found under mucous membrane of Small intrinsic glands found under mucous membrane of mouth, lips, cheeks and tongue - secrete at constant ratemouth, lips, cheeks and tongue - secrete at constant rate

3 pairs extrinsic glands connected to oral cavity by ducts3 pairs extrinsic glands connected to oral cavity by ducts parotid, submandibular and sublingualparotid, submandibular and sublingual

2121

Histology of Salivary GlandsHistology of Salivary Glands Compound tubuloacinar glandsCompound tubuloacinar glands Mucous cells secrete mucusMucous cells secrete mucus Serous cells secrete thin fluid rich Serous cells secrete thin fluid rich

in amylasein amylase Mixed acinus has bothMixed acinus has both

2222

SalivationSalivation Total of 1 to 1.5 L of saliva per dayTotal of 1 to 1.5 L of saliva per day Cells filter water from blood and add other substancesCells filter water from blood and add other substances Food stimulates receptors that signal salivatory Food stimulates receptors that signal salivatory

nuclei in medulla and ponsnuclei in medulla and pons parasympathetic stimulation parasympathetic stimulation salivary glands produce thin salivary glands produce thin

saliva, rich in enzymessaliva, rich in enzymes sympathetic stimulation sympathetic stimulation produce less abundant, thicker produce less abundant, thicker

saliva, with more mucussaliva, with more mucus

Higher brain centers stimulate salivatory nuclei so Higher brain centers stimulate salivatory nuclei so sight, smell and thought of food cause salivationsight, smell and thought of food cause salivation

2323

PharynxPharynx

Skeletal muscleSkeletal muscle deep layer – longitudinal orientationdeep layer – longitudinal orientation superficial layer – circular orientationsuperficial layer – circular orientation

superior, middle and inferior pharyngeal superior, middle and inferior pharyngeal constrictorsconstrictors

2424

EsophagusEsophagus

Straight muscular tube 25-30 cm longStraight muscular tube 25-30 cm long nonkeratinized stratified squamous epitheliumnonkeratinized stratified squamous epithelium esophageal glands in submucosaesophageal glands in submucosa skeletal muscle in upper part and smooth in bottom skeletal muscle in upper part and smooth in bottom

Extends from pharynx to cardiac stomach passing Extends from pharynx to cardiac stomach passing through esophageal hiatus in diaphragmthrough esophageal hiatus in diaphragm inferior pharyngeal constrictor excludes air from itinferior pharyngeal constrictor excludes air from it

Lower esophageal sphincter closes orifice to refluxLower esophageal sphincter closes orifice to reflux

2525

SwallowingSwallowing

2626

Swallowing (Deglutition)Swallowing (Deglutition) Series of muscular contractions coordinated by center Series of muscular contractions coordinated by center

in medulla and ponsin medulla and pons motor signals from cranial nerves V, VII, IX and XIImotor signals from cranial nerves V, VII, IX and XII

Buccal phaseBuccal phase tongue collects food and pushes it back into oropharynxtongue collects food and pushes it back into oropharynx

Pharyngeal-esophageal phasePharyngeal-esophageal phase soft palate rises and blocks nasopharynxsoft palate rises and blocks nasopharynx infrahyoid muscles lift larynx; epiglottis folded back infrahyoid muscles lift larynx; epiglottis folded back pharyngeal constrictors push bolus down esophaguspharyngeal constrictors push bolus down esophagus

liquids in 2 seconds -- food bolus may take 8 secondsliquids in 2 seconds -- food bolus may take 8 seconds lower esophageal sphincter relaxeslower esophageal sphincter relaxes

2727

X-ray: Swallowing in EsophagusX-ray: Swallowing in Esophagus

2828

StomachStomach Mechanically breaks up food, liquifies food Mechanically breaks up food, liquifies food

and begins chemical digestion of protein and and begins chemical digestion of protein and fatfat resulting soupy mixture is called chymeresulting soupy mixture is called chyme

Does not absorb significant amount of Does not absorb significant amount of nutrientsnutrients absorbs aspirin and some lipid-soluble drugsabsorbs aspirin and some lipid-soluble drugs

2929

Gross Anatomy of StomachGross Anatomy of Stomach Muscular sac Muscular sac (internal volume from 50ml to 4L)(internal volume from 50ml to 4L)

J - shaped organ with lesser and greater J - shaped organ with lesser and greater curvaturescurvatures

regional differencesregional differences cardiac region just inside cardiac orificecardiac region just inside cardiac orifice fundus - domed portion superior to esophageal openingfundus - domed portion superior to esophageal opening body - main portion of organbody - main portion of organ pyloric region - narrow inferior end pyloric region - narrow inferior end

antrum and pyloric canalantrum and pyloric canal

Pylorus - opening to duodenumPylorus - opening to duodenum thick ring of smooth muscle forms a sphincterthick ring of smooth muscle forms a sphincter

3030

Innervation and CirculationInnervation and Circulation

Innervation by Innervation by parasympathetic fibers from vagus parasympathetic fibers from vagus sympathetic fibers from celiac plexussympathetic fibers from celiac plexus

All blood from stomach enters hepatic All blood from stomach enters hepatic portal circulation and is filtered through portal circulation and is filtered through liver before returning to heartliver before returning to heart

3131

Gross Anatomy of StomachGross Anatomy of Stomach

Notice: bulge of fundus, narrowing of pyloric region, Notice: bulge of fundus, narrowing of pyloric region, thickness of pyloric sphincter and greater and thickness of pyloric sphincter and greater and lesser curvatureslesser curvatures

3232

Gross Anatomy of StomachGross Anatomy of Stomach

3333

Unique Features of Stomach Unique Features of Stomach WallWall

MucosaMucosa simple columnar glandular epitheliumsimple columnar glandular epithelium lamina propria is filled with tubular glands (gastric pits)lamina propria is filled with tubular glands (gastric pits)

Muscularis externa has 3 layersMuscularis externa has 3 layers outer longitudinal, middle circular and inner oblique layersouter longitudinal, middle circular and inner oblique layers

3434

Gastric GlandGastric Gland

3535

Cells of Gastric GlandsCells of Gastric Glands Mucous cells secrete mucusMucous cells secrete mucus Regenerative cells Regenerative cells

divide rapidly to produce new cells that divide rapidly to produce new cells that migrate to surfacemigrate to surface

Parietal cells Parietal cells secrete HCl acid and intrinsic factorsecrete HCl acid and intrinsic factor

Chief cells Chief cells secrete pepsinogen secrete pepsinogen chymosin and lipase in infancychymosin and lipase in infancy

Enteroendocrine cells Enteroendocrine cells secrete hormones and paracrine secrete hormones and paracrine

messengersmessengers

3636

Opening of Gastric PitOpening of Gastric Pit

3737

Gastric SecretionsGastric Secretions

2 to 3 L of gastric juice/day 2 to 3 L of gastric juice/day (H(H22O, HCl and pepsin)O, HCl and pepsin) Parietal cells contain carbonic anhydrase (CAH)Parietal cells contain carbonic anhydrase (CAH)

CAHCAH COCO22 + H + H22O O H H22COCO33 HCO HCO33-- + H + H++

HH++ is pumped into stomach lumen by H is pumped into stomach lumen by H++KK++ATPase ATPase antiporter uses ATP to pump Hantiporter uses ATP to pump H++ out and K out and K+ + inin

HCOHCO33-- exchanged for Cl exchanged for Cl-- (chloride shift)(chloride shift)

ClCl-- pumped out to join H pumped out to join H++ forming HCl forming HCl HCOHCO33

-- in blood causes alkaline tide (blood pH in blood causes alkaline tide (blood pH ))

3838

Functions of Hydrochloric AcidFunctions of Hydrochloric Acid

Activates pepsin and lingual lipaseActivates pepsin and lingual lipase Breaks up connective tissues and plant Breaks up connective tissues and plant

cell wallscell walls liquefies food to form chymeliquefies food to form chyme

Converts ingested ferric ions (FeConverts ingested ferric ions (Fe3+3+) to ) to ferrous ions (Feferrous ions (Fe2+2+)) absorbed and used for hemoglobin synthesisabsorbed and used for hemoglobin synthesis

Destroys ingested bacteria and pathogensDestroys ingested bacteria and pathogens

3939

Gastric Enzymes and Intrinsic Gastric Enzymes and Intrinsic FactorFactor Intrinsic factorIntrinsic factor

essential for Bessential for B1212 absorption by small intestine absorption by small intestine

RBC production RBC production (lack causes pernicious anemia)(lack causes pernicious anemia)

Pepsin - protein digestionPepsin - protein digestion secreted as pepsinogen secreted as pepsinogen (inactive)(inactive)

HCl converts it to pepsin HCl converts it to pepsin (active)(active)

Gastric lipase and chymosinGastric lipase and chymosin lipase digests butterfat of milk in infantlipase digests butterfat of milk in infant chymosin curdles milk by coagulating proteinschymosin curdles milk by coagulating proteins

4040

Chemical MessengersChemical Messengers Many produced by enteroendocrine cellsMany produced by enteroendocrine cells

hormones enter blood hormones enter blood distant cells distant cells paracrine secretions paracrine secretions neighboring cells neighboring cells

Gut-brain peptidesGut-brain peptides signaling molecules produced in digestive tract signaling molecules produced in digestive tract

and CNSand CNS

4141

Gastric MotilityGastric Motility Swallowing center signals stomach to relaxSwallowing center signals stomach to relax Food stretches stomach activating a receptive-Food stretches stomach activating a receptive-

relaxation responserelaxation response resists stretching briefly, but relaxes to hold more foodresists stretching briefly, but relaxes to hold more food

Rhythm of peristalsis controlled by pacemaker cells Rhythm of peristalsis controlled by pacemaker cells in longitudinal muscle layerin longitudinal muscle layer gentle ripple of contraction every 20 seconds churns and gentle ripple of contraction every 20 seconds churns and

mixes food with gastric juicemixes food with gastric juice stronger contraction at pyloric region; ejects 3 mlstronger contraction at pyloric region; ejects 3 ml typical meal emptied from stomach in 4 hourstypical meal emptied from stomach in 4 hours

4242

VomitingVomiting Induced by Induced by

excessive stretching of stomach, psychological excessive stretching of stomach, psychological stimuli or chemical irritants (bacterial toxins)stimuli or chemical irritants (bacterial toxins)

Emetic center in medulla causes Emetic center in medulla causes retchingretching

lower esophageal sphincter to relax lower esophageal sphincter to relax stomach and duodenum to contract spasmodicallystomach and duodenum to contract spasmodically

vomitingvomiting when abdominal contraction forces upper esophageal when abdominal contraction forces upper esophageal

sphincter to opensphincter to open

4343

Healthy Mucosa and Peptic Healthy Mucosa and Peptic UlcerUlcer

4444

Regulation of Gastric SecretionRegulation of Gastric Secretion

4545

Regulation of Gastric Function Regulation of Gastric Function (Phases 1-2)(Phases 1-2)

Cephalic phaseCephalic phase sight, smell, taste or thought of food; vagus nerve sight, smell, taste or thought of food; vagus nerve

stimulates gastric secretion and motilitystimulates gastric secretion and motility

Gastric phaseGastric phase activated by presence of food or semidigested activated by presence of food or semidigested

protein protein by stretch or by stretch or in pH in pH

secretion stimulated bysecretion stimulated by ACh ACh (from parasympathetic fibers),(from parasympathetic fibers), histamine histamine (from gastric (from gastric

enteroendocrine cells)enteroendocrine cells) and gastrin and gastrin (from pyloric G cells)(from pyloric G cells)

receptors on parietal and chief cellsreceptors on parietal and chief cells

4646

Regulation of Gastric Function Regulation of Gastric Function (Phase 3)(Phase 3)

Intestinal phase Intestinal phase - duodenum regulates gastric - duodenum regulates gastric activity through hormones and nervous reflexesactivity through hormones and nervous reflexes at first gastric activity increases at first gastric activity increases (if duodenum is (if duodenum is

stretched or amino acids in chyme cause gastrin release)stretched or amino acids in chyme cause gastrin release)

enterogastric reflex - duodenum inhibits stomachenterogastric reflex - duodenum inhibits stomach caused by acid and semi-digested fats in duodenumcaused by acid and semi-digested fats in duodenum

chyme stimulates duodenal cells to release chyme stimulates duodenal cells to release secretin, cholecystokinin (CCK) and gastric secretin, cholecystokinin (CCK) and gastric inhibitory peptideinhibitory peptide all 3 suppress gastric secretion and motilityall 3 suppress gastric secretion and motility

4747

Positive Feedback Control- Gastric Positive Feedback Control- Gastric SecretionSecretion

4848

Liver, Gallbladder and PancreasLiver, Gallbladder and Pancreas

All release important secretions into small All release important secretions into small intestine to continue digestionintestine to continue digestion

4949

Gross Anatomy of LiverGross Anatomy of Liver 3 lb. organ located inferior to the diaphragm3 lb. organ located inferior to the diaphragm 4 lobes - right, left, quadrate and caudate4 lobes - right, left, quadrate and caudate

falciform ligament separates left and rightfalciform ligament separates left and right round ligament, remnant of umbilical veinround ligament, remnant of umbilical vein

Gallbladder adheres to ventral surface between Gallbladder adheres to ventral surface between right and quadrate lobesright and quadrate lobes

5050

Inferior Surface of LiverInferior Surface of Liver

5151

Microscopic Anatomy of LiverMicroscopic Anatomy of Liver

Tiny cylinders called hepatic lobules (2mm by 1mm)Tiny cylinders called hepatic lobules (2mm by 1mm) Central vein surrounded by sheets of hepatocyte cells Central vein surrounded by sheets of hepatocyte cells

separated by sinusoids lined with fenestrated epitheliumseparated by sinusoids lined with fenestrated epithelium Blood filtered by hepatocytes on way to central veinBlood filtered by hepatocytes on way to central vein

5252

Histology of Liver - Hepatic Histology of Liver - Hepatic TriadTriad

3 structures found in corner between lobules3 structures found in corner between lobules hepatic portal vein and hepatic artery bring blood to liverhepatic portal vein and hepatic artery bring blood to liver bile duct collects bile from bile canaliculi between sheets of bile duct collects bile from bile canaliculi between sheets of

hepatocytes to be secreted from liver in hepatic ductshepatocytes to be secreted from liver in hepatic ducts

5353

Ducts of Gallbladder, Liver and Ducts of Gallbladder, Liver and PancreasPancreas

5454

Ducts Ducts of Gallbladder, Liver, Pancreasof Gallbladder, Liver, Pancreas

Bile passes from bile canaliculi between cells to bile Bile passes from bile canaliculi between cells to bile ductules to right and left hepatic ductsductules to right and left hepatic ducts

Right and left ducts join outside liver to form common Right and left ducts join outside liver to form common hepatic ducthepatic duct

Cystic duct from gallbladder joins common hepatic Cystic duct from gallbladder joins common hepatic duct to form bile ductduct to form bile duct

Duct of pancreas and bile duct combine to form Duct of pancreas and bile duct combine to form hepatopancreatic ampulla emptying into duodenum hepatopancreatic ampulla emptying into duodenum at major duodenal papillaat major duodenal papilla sphincter of Oddi (hepatopancreatic sphincter) regulates sphincter of Oddi (hepatopancreatic sphincter) regulates

release of bile and pancreatic juicerelease of bile and pancreatic juice

5555

Gallbladder and BileGallbladder and Bile Sac on underside of liver -- 10 cm longSac on underside of liver -- 10 cm long 500 to 1000 mL bile are secreted daily from liver500 to 1000 mL bile are secreted daily from liver Gallbladder stores and concentrates bileGallbladder stores and concentrates bile

bile backs up into gallbladder from a filled bile ductbile backs up into gallbladder from a filled bile duct between meals, bile is concentrated by factor of 20between meals, bile is concentrated by factor of 20

Yellow-green fluid containing minerals, bile acids, Yellow-green fluid containing minerals, bile acids, cholesterol, bile pigments and phospholipidscholesterol, bile pigments and phospholipids bilirubin pigment from hemoglobin breakdownbilirubin pigment from hemoglobin breakdown

intestinal bacteria convert to urobilinogen = brown colorintestinal bacteria convert to urobilinogen = brown color

bile acid (salts) emulsify fats and aid in their digestionbile acid (salts) emulsify fats and aid in their digestion enterohepatic circulation - recycling of bile acids from ileumenterohepatic circulation - recycling of bile acids from ileum

5656

Gross Anatomy of PancreasGross Anatomy of Pancreas Retroperitoneal gland posterior to stomachRetroperitoneal gland posterior to stomach

head, body and tailhead, body and tail

Endocrine and exocrine glandEndocrine and exocrine gland secretes insulin and glucagon into the bloodsecretes insulin and glucagon into the blood secretes 1500 mL pancreatic juice into duodenumsecretes 1500 mL pancreatic juice into duodenum

water, enzymes, zymogens, and sodium bicarbonatewater, enzymes, zymogens, and sodium bicarbonate other pancreatic enzymes are activated by exposure to bile and ions other pancreatic enzymes are activated by exposure to bile and ions

in the intestinein the intestine

Pancreatic duct runs length of gland to open at Pancreatic duct runs length of gland to open at sphincter of Oddisphincter of Oddi accessory duct opens independently on duodenumaccessory duct opens independently on duodenum

5757

Pancreatic Acinar CellsPancreatic Acinar Cells Zymogens Zymogens == proteases proteases

trypsinogentrypsinogen chymotrypsinogenchymotrypsinogen procarboxypeptidaseprocarboxypeptidase

Other enzymesOther enzymes amylaseamylase lipaselipase ribonuclease and ribonuclease and

deoxyribonucleasedeoxyribonuclease

5858

Activation of ZymogensActivation of Zymogens

Trypsinogen converted to trypsin by intestinal epitheliumTrypsinogen converted to trypsin by intestinal epithelium Trypsin converts other 2 (also digests dietary protein)Trypsin converts other 2 (also digests dietary protein)

5959

Hormonal Control of SecretionHormonal Control of Secretion Cholecystokinin released from duodenum in Cholecystokinin released from duodenum in

response to arrival of acid and fatresponse to arrival of acid and fat causes contraction of gallbladder, secretion of causes contraction of gallbladder, secretion of

pancreatic enzymes, relaxation of pancreatic enzymes, relaxation of hepatopancreatic sphincterhepatopancreatic sphincter

Secretin released from duodenum in response Secretin released from duodenum in response to acidic chymeto acidic chyme stimulates all ducts to secrete more bicarbonatestimulates all ducts to secrete more bicarbonate

Gastrin from stomach and duodenum weakly Gastrin from stomach and duodenum weakly stimulates gallbladder contraction and stimulates gallbladder contraction and pancreatic enzyme secretionpancreatic enzyme secretion

6060

Small IntestineSmall Intestine

Nearly all chemical digestion and nutrient absorption Nearly all chemical digestion and nutrient absorption occurs in small intestineoccurs in small intestine

6161

Small IntestineSmall Intestine Duodenum curves around head of pancreas Duodenum curves around head of pancreas (10 in.)(10 in.)

retroperitoneal along with pancreasretroperitoneal along with pancreas receives stomach contents, pancreatic juice and bilereceives stomach contents, pancreatic juice and bile neutralizes stomach acids, emulsifies fats, pepsin neutralizes stomach acids, emulsifies fats, pepsin

inactivated by pH increase, pancreatic enzymesinactivated by pH increase, pancreatic enzymes

Jejunum - next 8 ft. (in upper abdomen)Jejunum - next 8 ft. (in upper abdomen) has large tall circular folds; walls are thick, muscularhas large tall circular folds; walls are thick, muscular most digestion and nutrient absorption occur heremost digestion and nutrient absorption occur here

Ileum - last 12 ft. (in lower abdomen)Ileum - last 12 ft. (in lower abdomen) has peyer’s patches – clusters of lymphatic noduleshas peyer’s patches – clusters of lymphatic nodules ends at ileocecal junction with large intestineends at ileocecal junction with large intestine

6262

Circular folds Circular folds (plicae circularis)(plicae circularis) up to 10 mm tall up to 10 mm tall involve only mucosa and submucosainvolve only mucosa and submucosa chyme flows in spiral path causing more contactchyme flows in spiral path causing more contact

Small Intestine - Surface AreaSmall Intestine - Surface Area

Villi are fingerlike projections 1 Villi are fingerlike projections 1 mm tallmm tall contain blood vessels and contain blood vessels and

lymphatics (lacteal)lymphatics (lacteal) nutrient absorptionnutrient absorption

Microvilli 1 micron tall; Microvilli 1 micron tall;

cover surfacecover surface brush border on cellsbrush border on cells brush border enzymes for brush border enzymes for

final stages of digestionfinal stages of digestion

6363

Pores opening between villi lead Pores opening between villi lead to intestinal cryptsto intestinal crypts absorptive cells, goblet cells and at absorptive cells, goblet cells and at

base, rapidly dividing cellsbase, rapidly dividing cells life span of 3-6 days as migrate up to life span of 3-6 days as migrate up to

surface and get sloughed off and digestedsurface and get sloughed off and digested

paneth cells – antibacterial secretionspaneth cells – antibacterial secretions

Brunner’s glands in submucosa Brunner’s glands in submucosa secrete bicarbonate mucussecrete bicarbonate mucus

Peyer patches are populations of Peyer patches are populations of lymphocytes to fight pathogenslymphocytes to fight pathogens

Secrete 1-2 L of intestinal juice/daySecrete 1-2 L of intestinal juice/day water and mucus, pH 7.4-7.8water and mucus, pH 7.4-7.8

Intestinal CryptsIntestinal Crypts

6464

Intestinal VilliIntestinal Villi

Villi of Jejunum Histology of duodenum

6565

Intestinal MotilityIntestinal Motility1.1. Mixes chyme with intestinal juice, bile and Mixes chyme with intestinal juice, bile and

pancreatic juicepancreatic juice2.2. Churns chyme to increase contact with mucosa for Churns chyme to increase contact with mucosa for

absorption and digestionabsorption and digestion3.3. Moves residue towards large intestineMoves residue towards large intestine

segmentationsegmentation random ringlike constrictions mix and churn contentsrandom ringlike constrictions mix and churn contents 12 times per minute in duodenum12 times per minute in duodenum

peristaltic waves begin in duodenum but each one moves peristaltic waves begin in duodenum but each one moves further downfurther down push chyme along for 2 hourspush chyme along for 2 hours suppressed by refilling of stomachsuppressed by refilling of stomach

Food in stomach causes gastroileal reflex (relaxing Food in stomach causes gastroileal reflex (relaxing of valve and filling of cecum)of valve and filling of cecum)

6666

Segmentation in Small IntestineSegmentation in Small Intestine

Purpose of segmentation is to mix and churn not to move material along Purpose of segmentation is to mix and churn not to move material along as in peristalsisas in peristalsis

6767

PeristalsisPeristalsis Gradual movement of Gradual movement of

contents towards coloncontents towards colon Begins after absorption Begins after absorption

occursoccurs Migrating motor Migrating motor

complex controls complex controls waves of contractionwaves of contraction second wave begins second wave begins

distal to where first wave distal to where first wave beganbegan

6868

Carbohydrate Digestion - Small IntestineCarbohydrate Digestion - Small Intestine

Salivary amylase stops working in stomach (pH < 4.5)Salivary amylase stops working in stomach (pH < 4.5) 50% of dietary starch digested before it reaches small intestine50% of dietary starch digested before it reaches small intestine

Pancreatic amylase completes first step in 10 minutesPancreatic amylase completes first step in 10 minutes Brush border enzymes act upon oligosaccharides, maltose, Brush border enzymes act upon oligosaccharides, maltose,

sucrose, lactose and fructosesucrose, lactose and fructose lactose indigestible after age 4 in most humans (lactase declines)lactose indigestible after age 4 in most humans (lactase declines)

6969

Carbohydrate AbsorptionCarbohydrate Absorption

Sodium-glucose transport proteins (SGLT) in membrane help Sodium-glucose transport proteins (SGLT) in membrane help absorb glucose and galactoseabsorb glucose and galactose

Fructose absorbed by facilitated diffusion then converted to Fructose absorbed by facilitated diffusion then converted to glucose inside the cellglucose inside the cell

7070

Protein Digestion and Protein Digestion and AbsorptionAbsorption

Pepsin has optimal pH of 1.5 to 3.5 -- inactivated Pepsin has optimal pH of 1.5 to 3.5 -- inactivated when passes into duodenum and mixes with alkaline when passes into duodenum and mixes with alkaline pancreatic juice (pH 8)pancreatic juice (pH 8)

7171

Protein Digestion and Protein Digestion and AbsorptionAbsorption

Pancreatic enzymes take over protein digestion by Pancreatic enzymes take over protein digestion by hydrolyzing polypeptides into shorter oligopeptideshydrolyzing polypeptides into shorter oligopeptides

7272

Protein Digestion and Protein Digestion and AbsorptionAbsorption

Brush border enzymes finish task, producing amino acids that Brush border enzymes finish task, producing amino acids that are absorbed into intestinal epithelial cellsare absorbed into intestinal epithelial cells amino acid cotransporters move into epithelial cells and facilitated amino acid cotransporters move into epithelial cells and facilitated

diffusion moves amino acids out into blood streamdiffusion moves amino acids out into blood stream

Infants absorb proteins by pinocytosis (maternal IgA)Infants absorb proteins by pinocytosis (maternal IgA)

7373

Fat Digestion and AbsorptionFat Digestion and Absorption

7474

Fat Digestion and AbsorptionFat Digestion and Absorption

7575

Fat Digestion and AbsorptionFat Digestion and Absorption

7676

Nucleic Acids, Vitamins, and MineralsNucleic Acids, Vitamins, and Minerals Nucleases hydrolyze DNA and RNA to nucleotidesNucleases hydrolyze DNA and RNA to nucleotides

nucleosidases and phosphatases of brush border split nucleosidases and phosphatases of brush border split them into phosphate ions, ribose or deoxyribose sugar them into phosphate ions, ribose or deoxyribose sugar and nitrogenous basesand nitrogenous bases

Vitamins are absorbed unchangedVitamins are absorbed unchanged A, D, E and K with other lipids -- B complex and C by A, D, E and K with other lipids -- B complex and C by

simple diffusion and Bsimple diffusion and B1212 if bound to intrinsic factor if bound to intrinsic factor

Minerals are absorbed all along small intestineMinerals are absorbed all along small intestine NaNa++ cotransported with sugars and amino acids cotransported with sugars and amino acids ClCl-- exchanged for bicarbonate reversing stomach exchanged for bicarbonate reversing stomach Iron and calcium absorbed as neededIron and calcium absorbed as needed

7777

Water BalanceWater Balance

Digestive tract receives about 9 L of water/dayDigestive tract receives about 9 L of water/day .7 L in food, 1.6 L in drink, 6.7 L in secretions.7 L in food, 1.6 L in drink, 6.7 L in secretions 8 L is absorbed by small intestine and 0.8 L by large 8 L is absorbed by small intestine and 0.8 L by large

intestineintestine

Water is absorbed by osmosis following the Water is absorbed by osmosis following the absorption of salts and organic nutrientsabsorption of salts and organic nutrients

Diarrhea occurs when too little water is absorbedDiarrhea occurs when too little water is absorbed feces pass through too quickly if irritatedfeces pass through too quickly if irritated feces contains high concentrations of a solute feces contains high concentrations of a solute

(lactose)(lactose)

7878

Anatomy of Large IntestineAnatomy of Large Intestine

7979

Gross Anatomy of Large IntestineGross Anatomy of Large Intestine

5 feet long and 2.5 inches in diameter in 5 feet long and 2.5 inches in diameter in cadavercadaver

Begins as cecum and appendix in lower right Begins as cecum and appendix in lower right cornercorner

Ascending, transverse and descending colon Ascending, transverse and descending colon frame the small intestineframe the small intestine

Sigmoid colon is S-shaped portion leading Sigmoid colon is S-shaped portion leading down into pelvisdown into pelvis

Rectum - straight portion ending at anal canalRectum - straight portion ending at anal canal

8080

Microscopic AnatomyMicroscopic Anatomy

Mucosa - simple columnar epithelium Mucosa - simple columnar epithelium anal canal has stratified squamous epitheliumanal canal has stratified squamous epithelium

No circular folds or villi to increase surface areaNo circular folds or villi to increase surface area Intestinal crypts (glands sunken into lamina propria) Intestinal crypts (glands sunken into lamina propria)

produce mucus onlyproduce mucus only Muscularis externaMuscularis externa

muscle tone in longitudinal muscle fibers (concentrated in muscle tone in longitudinal muscle fibers (concentrated in taeniae coli) form pouches (haustra)taeniae coli) form pouches (haustra)

Transverse and sigmoid have a serosa, rest Transverse and sigmoid have a serosa, rest retroperitoneal retroperitoneal epiploic appendages are suspended fatty sacsepiploic appendages are suspended fatty sacs

8181

Bacterial Flora and Intestinal Bacterial Flora and Intestinal GasGas

Bacterial flora populate large intestineBacterial flora populate large intestine ferment cellulose and other undigested ferment cellulose and other undigested

carbohydrates; we absorb resulting sugarscarbohydrates; we absorb resulting sugars synthesize vitamins B and Ksynthesize vitamins B and K

Flatus (gas)Flatus (gas) average person produces 500 mL per dayaverage person produces 500 mL per day most is swallowed air but hydrogen sulfide, most is swallowed air but hydrogen sulfide,

indole and skatole produce odorindole and skatole produce odor

8282

Absorption and MotilityAbsorption and Motility

Transit time is 12 to 24 hoursTransit time is 12 to 24 hours reabsorbs water and electrolytesreabsorbs water and electrolytes

Feces consist of water and solids (bacteria, mucus, Feces consist of water and solids (bacteria, mucus, undigested fiber, fat and sloughed epithelial cellsundigested fiber, fat and sloughed epithelial cells

Haustral contractions occur every 30 minutesHaustral contractions occur every 30 minutes distension of a haustrum stimulates it to contractdistension of a haustrum stimulates it to contract

Mass movements occur 1 to 3 times a dayMass movements occur 1 to 3 times a day triggered by gastrocolic and duodenocolic reflexestriggered by gastrocolic and duodenocolic reflexes

filling of the stomach and duodenum stimulates motilityfilling of the stomach and duodenum stimulates motility moves residue for several centimeters with each contractionmoves residue for several centimeters with each contraction

8383

Anatomy of Anal CanalAnatomy of Anal Canal

Anal canal is 3 cm total lengthAnal canal is 3 cm total length Anal columns are longitudinal ridges separated by Anal columns are longitudinal ridges separated by

mucus secreting anal sinusesmucus secreting anal sinuses Hemorrhoids are permanently distended veinsHemorrhoids are permanently distended veins

8484

DefecationDefecation Stretching of the rectum stimulates defecationStretching of the rectum stimulates defecation

intrinsic defecation reflex via the myenteric plexus intrinsic defecation reflex via the myenteric plexus causes muscularis to contract and internal sphincter to relaxcauses muscularis to contract and internal sphincter to relax

relatively weak contractionsrelatively weak contractions

defecation occurs only if external anal sphincter is voluntarily defecation occurs only if external anal sphincter is voluntarily relaxedrelaxed

parasympathetic defecation reflex involves spinal cordparasympathetic defecation reflex involves spinal cord stretching of rectum sends sensory signals to spinal cordstretching of rectum sends sensory signals to spinal cord splanchnic nerves return signals intensifying peristalsissplanchnic nerves return signals intensifying peristalsis

Abdominal contractions increase abdominal Abdominal contractions increase abdominal pressure as levator ani lifts anal canal upwards pressure as levator ani lifts anal canal upwards feces will fall awayfeces will fall away

8585

Neural Control of DefecationNeural Control of Defecation

1. Filling of the rectum1. Filling of the rectum

2. Reflex contraction of 2. Reflex contraction of rectum and relaxation rectum and relaxation of internal anal of internal anal sphinctersphincter

3. Voluntary relaxation of 3. Voluntary relaxation of external sphincterexternal sphincter