11

Chapter 24Chapter 24The Digestive SystemThe Digestive System

• Structure Structure – Gross Gross

AnatomyAnatomy– HistologyHistology

• FunctionFunction– MechanicalMechanical– ChemicalChemical

• DevelopmentDevelopment

• DisordersDisorders

22

Overview of GI tract Overview of GI tract FunctionsFunctions

• Mouth---bite, chew, swallowMouth---bite, chew, swallow

• Pharynx and esophagus----Pharynx and esophagus----transporttransport

• Stomach----mechanical Stomach----mechanical disruption; absorption of disruption; absorption of water & alcoholwater & alcohol

• Small intestine--chemical & Small intestine--chemical & mechanical digestion & mechanical digestion & absorptionabsorption

• Large intestine----absorb Large intestine----absorb electrolytes & vitamins (B and electrolytes & vitamins (B and K)K)

• Rectum and anus---defecationRectum and anus---defecation

33

Layers of the GI TractLayers of the GI Tract

1. Mucosal 1. Mucosal layerlayer

2. Submucosal 2. Submucosal layerlayer

3. Muscularis 3. Muscularis layerlayer

4. Serosa layer4. Serosa layer

44

MucosaMucosa• EpitheliumEpithelium

– stratified squamous(in mouth,esophagus & anus) = tough stratified squamous(in mouth,esophagus & anus) = tough – simple columnar in the restsimple columnar in the rest

• secretes enzymes and absorbs nutrientssecretes enzymes and absorbs nutrients

• specialized cells (goblet) secrete mucous onto cell surfacesspecialized cells (goblet) secrete mucous onto cell surfaces

• enteroendocrine cells---secrete hormones controlling organ enteroendocrine cells---secrete hormones controlling organ functionfunction

• Lamina propriaLamina propria– thin layer of loose connective tissuethin layer of loose connective tissue– contains BV and lymphatic tissuecontains BV and lymphatic tissue

• Muscularis mucosaeMuscularis mucosae---thin layer of smooth muscle---thin layer of smooth muscle– causes folds to form in mucosal layercauses folds to form in mucosal layer – increases local movements increasing absorption with exposure to “new” increases local movements increasing absorption with exposure to “new”

nutrientsnutrients

55

SubmucosaSubmucosa

• Loose connective tissueLoose connective tissue– containing BV, glands and lymphatic tissuecontaining BV, glands and lymphatic tissue

• Meissner’s plexus---Meissner’s plexus---– parasympatheticparasympathetic– innervationinnervation

• vasoconstrictionvasoconstriction

• local movement bylocal movement by muscularis mucosa muscularis mucosa smooth muscle smooth muscle

66

Muscularis Muscularis

• Skeletal muscle = voluntary controlSkeletal muscle = voluntary control– in mouth, pharynx , upper esophagus and in mouth, pharynx , upper esophagus and

anusanus– control over swallowing and defecationcontrol over swallowing and defecation

• Smooth muscle = involuntary controlSmooth muscle = involuntary control– inner circular fibers & outer longitudinal inner circular fibers & outer longitudinal

fibersfibers– mixes, crushes & propels food along by mixes, crushes & propels food along by

peristalsisperistalsis

77

SerosaSerosa

• An example of a serous membraneAn example of a serous membrane

• Covers all organs and walls of Covers all organs and walls of cavities not open to the outside of cavities not open to the outside of the bodythe body

• Secretes slippery fluidSecretes slippery fluid

• Consists of connective tissue covered Consists of connective tissue covered with simple squamous epitheliumwith simple squamous epithelium

88

PeritoneumPeritoneum

• PeritoneumPeritoneum– visceral layer covers visceral layer covers

organsorgans– parietal layer lines parietal layer lines

the walls of body the walls of body cavitycavity

• Peritoneal cavityPeritoneal cavity– potential space potential space

containing a bit of containing a bit of serous fluidserous fluid

99

Parts of the PeritoneumParts of the Peritoneum• MesenteryMesentery

• MesocolonMesocolon

• Lesser omentumLesser omentum

• Greater omentumGreater omentum

• Peritonitis = Peritonitis = inflammationinflammation– trauma trauma – rupture of GI tractrupture of GI tract– appendicitisappendicitis– perforated ulcerperforated ulcer

1010

Greater Omentum, Greater Omentum, Mesentery & MesocolonMesentery & Mesocolon

1111

Lesser OmentumLesser Omentum

1212

PeritonitisPeritonitis

• Acute inflammation of the Acute inflammation of the peritoneumperitoneum

• CauseCause– contamination by infectious microbes contamination by infectious microbes

during surgery or from rupture of during surgery or from rupture of abdominal organsabdominal organs

1313

MouthMouth

• Lips and cheeks-----contains buccinator muscle that Lips and cheeks-----contains buccinator muscle that keeps food between upper & lower teethkeeps food between upper & lower teeth

• Vestibule---area between cheeks and teethVestibule---area between cheeks and teeth• Oral cavity proper---the roof = hard, soft palate and Oral cavity proper---the roof = hard, soft palate and

uvulauvula– floor = the tongue floor = the tongue

1414

Pharyngeal ArchesPharyngeal Arches• Two skeletal musclesTwo skeletal muscles

• Palatoglossal musclePalatoglossal muscle– extends from palate to extends from palate to

tonguetongue– forms the first archforms the first arch– posterior limit of the posterior limit of the

mouthmouth

• Palatopharyngeal Palatopharyngeal musclemuscle– extends from palate to extends from palate to

pharyngeal wallpharyngeal wall– forms the second archforms the second arch– behind the palatine tonsilbehind the palatine tonsil

1515

Salivary GlandsSalivary Glands

• Parotid below your ear and over the masseterParotid below your ear and over the masseter

• Submandibular is under lower edge of mandibleSubmandibular is under lower edge of mandible

• Sublingual is deep to the tongue in floor of mouthSublingual is deep to the tongue in floor of mouth

• All have ducts that empty into the oral cavityAll have ducts that empty into the oral cavity

1616

Composition and Functions of Composition and Functions of SalivaSaliva

• Wet food for easier swallowingWet food for easier swallowing

• Dissolves food for tastingDissolves food for tasting

• Bicarbonate ions buffer acidic foodsBicarbonate ions buffer acidic foods– bulemia---vomiting hurts the enamel on your bulemia---vomiting hurts the enamel on your

teethteeth

• Chemical digestion of starch begins with Chemical digestion of starch begins with enzyme (salivary amylase)enzyme (salivary amylase)

• Enzyme (lysozyme) ---helps destroy bacteriaEnzyme (lysozyme) ---helps destroy bacteria

• Protects mouth from infection with its Protects mouth from infection with its rinsing action---1 to 1 and 1/2qts/dayrinsing action---1 to 1 and 1/2qts/day

1717

SalivationSalivation• Increase salivationIncrease salivation

– sight, smell, sounds, memory of food, sight, smell, sounds, memory of food, tongue stimulation---rock in mouthtongue stimulation---rock in mouth

• Stop salivation Stop salivation – dry mouth when you are afraiddry mouth when you are afraid– sympathetic nervessympathetic nerves

1818

MumpsMumps• Myxovirus Myxovirus that attacks the parotid glandthat attacks the parotid gland

• SymptomsSymptoms– inflammation and enlargement of the inflammation and enlargement of the

parotidparotid– fever, malaise & sour throat (especially fever, malaise & sour throat (especially

swallowing sour foods)swallowing sour foods)– swelling on one or both sidesswelling on one or both sides

• Sterility rarely possible in males with Sterility rarely possible in males with testicular involvement (only one side testicular involvement (only one side involved)involved)

• Vaccine available since 1967Vaccine available since 1967

1919

Structure and Function of the Structure and Function of the TongueTongue

• Muscle of tongue Muscle of tongue is attached to is attached to hyoid, mandible, hyoid, mandible, hard palate and hard palate and styloid processstyloid process

• Papillae are the Papillae are the bumps---taste bumps---taste buds are buds are protected by protected by being on the sides being on the sides of papillaeof papillae

2020

Tooth StructureTooth Structure

• CrownCrown

• NeckNeck

• RootsRoots

• Pulp Pulp cavitycavity

2121

Composition of TeethComposition of Teeth• EnamelEnamel

– hardest substance in hardest substance in bodybody

– calcium phosphate or calcium phosphate or carbonatecarbonate

• DentinDentin– calcified connective calcified connective

tissuetissue

• CementumCementum– bone-likebone-like– periodontal ligament periodontal ligament

penetrates itpenetrates it

What is the gingiva?

2222

DentitionDentition• Primary or baby teethPrimary or baby teeth

– 20 teeth that start erupting at 6 months20 teeth that start erupting at 6 months– 1 new pair of teeth per month1 new pair of teeth per month

• Permanent teethPermanent teeth– 32 teeth that erupt between 6 and 12 years 32 teeth that erupt between 6 and 12 years

of ageof age– differing structures indicate functiondiffering structures indicate function

• incisors for bitingincisors for biting

•canines or cuspids for tearingcanines or cuspids for tearing

•premolars & molars for crushing and grinding premolars & molars for crushing and grinding foodfood

2323

Primary and Secondary Primary and Secondary DentitionDentition

2424

Digestion in the MouthDigestion in the Mouth• Mechanical digestion (mastication or chewing)Mechanical digestion (mastication or chewing)

•breaks into piecesbreaks into pieces•mixes with saliva so it forms a bolus mixes with saliva so it forms a bolus

• Chemical digestionChemical digestion– amylaseamylase

•begins starch digestion at pH of 6.5 or 7.0 found in begins starch digestion at pH of 6.5 or 7.0 found in mouthmouth

•when bolus & enzyme hit the pH 2.5 gastric juices when bolus & enzyme hit the pH 2.5 gastric juices hydrolysis ceaseshydrolysis ceases

– lingual lipaselingual lipase•secreted by glands in tonguesecreted by glands in tongue•begins breakdown of triglycerides into fatty acids and begins breakdown of triglycerides into fatty acids and

glycerolglycerol

2525

PharynxPharynx• Funnel-shaped tube extending from internal Funnel-shaped tube extending from internal

nares to the esophagus (posteriorly) and nares to the esophagus (posteriorly) and larynx (anteriorly)larynx (anteriorly)

• Skeletal muscle lined by mucous membraneSkeletal muscle lined by mucous membrane• Deglutition or swallowing is facilitated by Deglutition or swallowing is facilitated by

saliva and mucussaliva and mucus– starts when bolus is pushed into the oropharynxstarts when bolus is pushed into the oropharynx– sensory nerves send signals to deglutition center sensory nerves send signals to deglutition center

in brainstemin brainstem– soft palate is lifted to close nasopharynxsoft palate is lifted to close nasopharynx– larynx is lifted as epiglottis is bent to cover larynx is lifted as epiglottis is bent to cover

glottisglottis

2626

EsophagusEsophagus

• Collapsed muscular Collapsed muscular tubetube

• In front of vertebraeIn front of vertebrae

• Posterior to tracheaPosterior to trachea

• Posterior to the heart Posterior to the heart

• Pierces the Pierces the diaphragm at hiatusdiaphragm at hiatus– hiatal hernia or hiatal hernia or

diaphragmatic herniadiaphragmatic hernia

2727

Histology of the EsophagusHistology of the Esophagus• Mucosa = stratified squamousMucosa = stratified squamous

• Submucosa = large mucous glandsSubmucosa = large mucous glands

• Muscularis = upper 1/3 is skeletal, middle Muscularis = upper 1/3 is skeletal, middle is mixed, lower 1/3 is smoothis mixed, lower 1/3 is smooth– upper & lower esophageal sphincters are upper & lower esophageal sphincters are

prominent circular muscleprominent circular muscle

• Adventitia = connective tissue blending Adventitia = connective tissue blending with surrounding connective tissue--no with surrounding connective tissue--no peritoneumperitoneum

2828

Physiology of the Esophagus - Physiology of the Esophagus - SwallowingSwallowing

• Voluntary phase---tongue pushes food to back of Voluntary phase---tongue pushes food to back of oral cavityoral cavity

• Involuntary phase----pharyngeal stageInvoluntary phase----pharyngeal stage– breathing stops & airways are closedbreathing stops & airways are closed– soft palate & uvula are lifted to close off nasopharynxsoft palate & uvula are lifted to close off nasopharynx– vocal cords closevocal cords close– epiglottis is bent over airway as larynx is liftedepiglottis is bent over airway as larynx is lifted

2929

SwallowingSwallowing

• Upper sphincter relaxes when Upper sphincter relaxes when larynx is lifted larynx is lifted

• Peristalsis pushes food downPeristalsis pushes food down– circular fibers behind bolus circular fibers behind bolus – longitudinal fibers in front of bolus shorten longitudinal fibers in front of bolus shorten

the distance of travelthe distance of travel

• Travel time is 4-8 seconds for solids and Travel time is 4-8 seconds for solids and 1 sec for liquids1 sec for liquids

• Lower sphincter relaxes as food Lower sphincter relaxes as food approachesapproaches

3030

Gastroesophageal Reflex Gastroesophageal Reflex DiseaseDisease• If lower sphincter fails to openIf lower sphincter fails to open

– distension of esophagus feels like chest pain or heart distension of esophagus feels like chest pain or heart attackattack

• If lower esophageal sphincter fails to closeIf lower esophageal sphincter fails to close– stomach acids enter esophagus & cause heartburn stomach acids enter esophagus & cause heartburn

(GERD)(GERD)– for a weak sphincter---don't eat a large meal and lay for a weak sphincter---don't eat a large meal and lay

down in front of TVdown in front of TV– smoking and alcohol make the sphincter relax smoking and alcohol make the sphincter relax

worsening the situationworsening the situation

• Control the symptoms by avoidingControl the symptoms by avoiding– coffee, chocolate, tomatoes, fatty foods, onions & mintcoffee, chocolate, tomatoes, fatty foods, onions & mint– take Tagamet HB or Pepcid AC 60 minutes before eatingtake Tagamet HB or Pepcid AC 60 minutes before eating– neutralize existing stomach acids with Tumsneutralize existing stomach acids with Tums

3131

Anatomy of StomachAnatomy of Stomach• Which side is it on? Which side is it on? • Size when empty?Size when empty?

– large sausagelarge sausage– stretches due to rugaestretches due to rugae

• Parts of stomachParts of stomach– cardiacardia– fundus---air in x-rayfundus---air in x-ray– bodybody– pylorus---starts to narrow as approaches pylorus---starts to narrow as approaches

pyloric sphincterpyloric sphincter

• Empties as small squirts of chyme leave Empties as small squirts of chyme leave the stomach through the pyloric valvethe stomach through the pyloric valve

3232

Pylorospasm and Pyloric Pylorospasm and Pyloric StenosisStenosis

• Abnormalities of the pyloric Abnormalities of the pyloric sphincter in infantssphincter in infants

• PylorospasmPylorospasm– muscle fibers of sphincter fail to relax muscle fibers of sphincter fail to relax

trapping food in the stomach trapping food in the stomach – vomiting occurs to relieve pressurevomiting occurs to relieve pressure

• Pyloric stenosisPyloric stenosis– narrowing of sphincter indicated by narrowing of sphincter indicated by

projectile vomitingprojectile vomiting– must be corrected surgicallymust be corrected surgically

3333

Histology of the StomachHistology of the Stomach

3434

Mucosa & Gastric GlandsMucosa & Gastric Glands• Hydrochloric acid Hydrochloric acid

converts pepsinogen converts pepsinogen from chief cell to from chief cell to pepsinpepsin

• Intrinsic factorIntrinsic factor– absorption of vitamin absorption of vitamin

B12 for RBC productionB12 for RBC production

• Gastrin hormone (g Gastrin hormone (g cell)cell)– “ “get it out of here”get it out of here”

• release more gastric juicerelease more gastric juice

• increase gastric motilityincrease gastric motility

• relax pyloric sphincterrelax pyloric sphincter

• constrict esophageal constrict esophageal sphincter preventing sphincter preventing entryentry

3535

MuscularisMuscularis

• Three layers of Three layers of smooth muscle--smooth muscle--outer outer longitudinal, longitudinal, circular & inner circular & inner obliqueoblique

• Permits greater Permits greater churning & churning & mixing of food mixing of food with gastric juicewith gastric juice

3636

Physiology--MPhysiology--Mechanical echanical DigestionDigestion

• Gentle mixing waves Gentle mixing waves – every 15 to 25 secondsevery 15 to 25 seconds– mixes bolus with 2 quarts/day of gastric mixes bolus with 2 quarts/day of gastric

juice to turn it into chyme (a thin liquid)juice to turn it into chyme (a thin liquid)

• More vigorous waves More vigorous waves – travel from body of stomach to pyloric travel from body of stomach to pyloric

regionregion

• Intense waves near the pylorus Intense waves near the pylorus – open it and squirt out 1-2 teaspoons full open it and squirt out 1-2 teaspoons full

with each wavewith each wave

3737

Physiology--Chemical Physiology--Chemical DigestionDigestion• Protein digestion beginsProtein digestion begins

– HCl denatures (unfolds) protein moleculesHCl denatures (unfolds) protein molecules– HCl transforms pepsinogen into pepsin that HCl transforms pepsinogen into pepsin that

breaks peptides bonds between certain amino breaks peptides bonds between certain amino acidsacids

• Fat digestion continuesFat digestion continues– gastric lipase splits the triglycerides in gastric lipase splits the triglycerides in milk fatmilk fat

•most effective at pH 5 to 6 (infant stomach)most effective at pH 5 to 6 (infant stomach)

• HCl kills microbes in foodHCl kills microbes in food• Mucous cells protect stomach walls from Mucous cells protect stomach walls from

being digested with 1-3mm thick layer of being digested with 1-3mm thick layer of mucousmucous

3838

Absorption of Nutrients by the Absorption of Nutrients by the StomachStomach• Water especially if it is coldWater especially if it is cold

• ElectrolytesElectrolytes

• Some drugs (especially aspirin) & alcoholSome drugs (especially aspirin) & alcohol

• Fat content in the stomach slows the passage of alcohol to Fat content in the stomach slows the passage of alcohol to the intestine where absorption is more rapid the intestine where absorption is more rapid

• Gastric mucosal cells contain alcohol dehydrogenase that Gastric mucosal cells contain alcohol dehydrogenase that converts some alcohol to acetaldehyde-----more of this converts some alcohol to acetaldehyde-----more of this enzyme found in males than femalesenzyme found in males than females

• Females have less total body fluid that same size male so Females have less total body fluid that same size male so end up with higher blood alcohol levels with same intake of end up with higher blood alcohol levels with same intake of alcoholalcohol

3939

Regulation of Gastric Regulation of Gastric EmptyingEmptying• Release of chyme is regulated by Release of chyme is regulated by

neural and hormonal reflexesneural and hormonal reflexes

• Distention & stomach contents Distention & stomach contents increase secretion of gastrin increase secretion of gastrin hormone & vagal nerve impulseshormone & vagal nerve impulses

– stimulate contraction of esophageal stimulate contraction of esophageal sphincter and stomach and relaxation sphincter and stomach and relaxation of pyloric sphincterof pyloric sphincter

4040

Vomiting (emesis)Vomiting (emesis)• Forceful expulsion of contents of stomach & Forceful expulsion of contents of stomach &

duodenum through the mouthduodenum through the mouth• CauseCause

– irritation or distension of stomachirritation or distension of stomach– unpleasant sights, general anesthesia, dizziness & certain unpleasant sights, general anesthesia, dizziness & certain

drugsdrugs

• Sensory input from medulla cause stomach Sensory input from medulla cause stomach contraction & complete sphincter relaxationcontraction & complete sphincter relaxation

• Contents of stomach squeezed between abdominal Contents of stomach squeezed between abdominal muscles and diaphragm and forced through open muscles and diaphragm and forced through open mouthmouth

• Serious because loss of acidic gastric juice can lead Serious because loss of acidic gastric juice can lead to alkalosisto alkalosis

4141

Anatomy of the PancreasAnatomy of the Pancreas• 5" long by 1" thick5" long by 1" thick

• Head close to curve in Head close to curve in C-shaped duodenumC-shaped duodenum

• Main duct joins Main duct joins common bile duct common bile duct from liver from liver

• Sphincter of Oddi on Sphincter of Oddi on major duodenal papillamajor duodenal papilla

• Opens 4" below Opens 4" below pyloric sphincterpyloric sphincter

4242

Composition and Functions of Composition and Functions of Pancreatic JuicePancreatic Juice• 1 & 1/2 Quarts/day at pH of 7.1 to 8.21 & 1/2 Quarts/day at pH of 7.1 to 8.2

• Contains water, enzymes & sodium Contains water, enzymes & sodium bicarbonatebicarbonate

• Digestive enzymesDigestive enzymes– ribonuclease----to digest nucleic acidsribonuclease----to digest nucleic acids– deoxyribonucleasedeoxyribonuclease

4343

PancreatitisPancreatitis

• Pancreatitis---inflammation of the Pancreatitis---inflammation of the pancreas occurring with the mumpspancreas occurring with the mumps

• Acute pancreatitis---associated with Acute pancreatitis---associated with heavy alcohol intake or biliary tract heavy alcohol intake or biliary tract obstructionobstruction– result is patient secretes trypsin in the result is patient secretes trypsin in the

pancreas & starts to digest himselfpancreas & starts to digest himself

4444

Regulation of Pancreatic Regulation of Pancreatic SecretionsSecretions

• SecretinSecretin– acidity in intestine acidity in intestine

causes increased causes increased sodium bicarbonate sodium bicarbonate releaserelease

4545

Anatomy of the Liver and Anatomy of the Liver and GallbladderGallbladder

• LiverLiver– weighs 3 lbs.weighs 3 lbs.– below diaphragm below diaphragm – right lobe largerright lobe larger– gallbladder on right gallbladder on right

lobe lobe – size causes right size causes right

kidney to be lower kidney to be lower than leftthan left

• GallbladderGallbladder– fundus, body & fundus, body &

neckneck

4646

Flow of Fluids Within the Flow of Fluids Within the LiverLiver

4747

Pathway of Bile SecretionPathway of Bile Secretion

• Bile capillariesBile capillaries

• Hepatic ducts connect to form common Hepatic ducts connect to form common hepatic ducthepatic duct

• Cystic duct from gallbladder & common Cystic duct from gallbladder & common hepatic duct join to form common bile ducthepatic duct join to form common bile duct

• Common bile duct & pancreatic duct empty Common bile duct & pancreatic duct empty into duodenuminto duodenum

4848

Blood Supply to the LiverBlood Supply to the Liver• Hepatic portal veinHepatic portal vein

– nutrient rich blood nutrient rich blood from stomach, from stomach, spleen & intestinesspleen & intestines

• Hepatic artery Hepatic artery from branch off from branch off the aortathe aorta

4949

Bile ProductionBile Production

• One quart of bile/day is secreted by the liverOne quart of bile/day is secreted by the liver– yellow-green in color & pH 7.6 to 8.6yellow-green in color & pH 7.6 to 8.6

• ComponentsComponents– water & cholesterolwater & cholesterol– bile salts = Na & K salts of bile acids bile salts = Na & K salts of bile acids – bile pigments (bilirubin) from hemoglobin bile pigments (bilirubin) from hemoglobin

molecule molecule •globin = a reuseable protein globin = a reuseable protein

•heme = broken down into iron and bilirubinheme = broken down into iron and bilirubin

5050

Regulation of Bile SecretionRegulation of Bile Secretion

5151

Liver Functions--Carbohydrate Liver Functions--Carbohydrate MetabolismMetabolism

• Turn proteins into glucoseTurn proteins into glucose

• Turn triglycerides into Turn triglycerides into glucoseglucose

• Turn excess glucose into Turn excess glucose into glycogen & store in the liverglycogen & store in the liver

• Turn glycogen back into Turn glycogen back into glucose as neededglucose as needed

5252

Liver Functions --Lipid Liver Functions --Lipid MetabolismMetabolism

• Synthesize cholesterolSynthesize cholesterol

• Synthesize lipoproteins----HDL Synthesize lipoproteins----HDL and LDL(used to transport and LDL(used to transport fatty acids in bloodstream)fatty acids in bloodstream)

• Stores some fatStores some fat

• Breaks down some fatty acidsBreaks down some fatty acids

5353

Liver Functions--Protein Liver Functions--Protein MetabolismMetabolism

• Deamination = removes NH2 (amine Deamination = removes NH2 (amine group) from amino acids so can use group) from amino acids so can use what is left as energy sourcewhat is left as energy source

• Converts resulting toxic ammonia Converts resulting toxic ammonia (NH3) into urea for excretion by the (NH3) into urea for excretion by the kidneykidney

• Synthesizes plasma proteins utilized in Synthesizes plasma proteins utilized in the clotting mechanism and immune the clotting mechanism and immune systemsystem

• Convert one amino acid into anotherConvert one amino acid into another

5454

Other Liver FunctionsOther Liver Functions• Detoxifies the blood by removing or altering Detoxifies the blood by removing or altering

drugs & hormones(thyroid & estrogen)drugs & hormones(thyroid & estrogen)

• Removes the waste product--bilirubinRemoves the waste product--bilirubin

• Releases bile salts help digestion by Releases bile salts help digestion by emulsificationemulsification

• Stores fat soluble vitamins-----A, B12, D, E, KStores fat soluble vitamins-----A, B12, D, E, K

• Stores iron and copperStores iron and copper

• Phagocytizes worn out blood cells & bacteriaPhagocytizes worn out blood cells & bacteria

• Activates vitamin D (the skin can also do this Activates vitamin D (the skin can also do this with 1 hr of sunlight a week) with 1 hr of sunlight a week)

5555

Summary of Digestive Summary of Digestive HormonesHormones• GastrinGastrin

– stomach, gastric & ileocecal sphinctersstomach, gastric & ileocecal sphincters

• Gastric inhibitory peptide--GIPGastric inhibitory peptide--GIP– stomach & pancreasstomach & pancreas

• SecretinSecretin– pancreas, liver & stomachpancreas, liver & stomach

• Cholecystokinin--CCKCholecystokinin--CCK– pancreas, gallbladder, sphincter of pancreas, gallbladder, sphincter of

Oddi, & stomachOddi, & stomach

5656

Anatomy of the Small IntestineAnatomy of the Small Intestine

• 20 feet long----1 inch in diameter20 feet long----1 inch in diameter

• Large surface area for majority of Large surface area for majority of absorptionabsorption

• 3 parts3 parts– duodenum---10 inchesduodenum---10 inches– jejunum---8 feetjejunum---8 feet– ileum---12 feetileum---12 feet

•ends at ileocecal valveends at ileocecal valve

5757

Histology of Small IntestineHistology of Small Intestine

5858

Histology of the Small Histology of the Small IntestineIntestine• Structures that increase surface areaStructures that increase surface area

– plica circularisplica circularis•permanent ½ inch tall folds that contain part permanent ½ inch tall folds that contain part

of submucosal layerof submucosal layer•not found in lower ileumnot found in lower ileum•can not stretch out like rugae in stomachcan not stretch out like rugae in stomach

– villivilli•1 Millimeter tall1 Millimeter tall•Contains vascular capillaries and Contains vascular capillaries and

lacteals(lymphatic capillaries)lacteals(lymphatic capillaries)

– microvillimicrovilli•cell surface feature known as brush bordercell surface feature known as brush border

5959

Functions of MicrovilliFunctions of Microvilli

• Absorption and digestionAbsorption and digestion

• Digestive enzymes found at cell Digestive enzymes found at cell surface on microvillisurface on microvilli

• Digestion occurs at cell surfacesDigestion occurs at cell surfaces

• Significant cell division within Significant cell division within intestinal glands produces new cells intestinal glands produces new cells that move up that move up

• Once out of the way---rupturing and Once out of the way---rupturing and releasing their digestive enzymes & releasing their digestive enzymes & proteinsproteins

6060

Cells of Intestinal GlandsCells of Intestinal Glands

• Absorptive cellAbsorptive cell

• Goblet cellGoblet cell

• EnteroendocrinEnteroendocrinee

• Paneth cellsPaneth cells– secretes secretes

lysozymelysozyme

6161

Goblet Cells of GI Goblet Cells of GI epitheliumepithelium

Unicellular glands that are part of simple columnar epithelium

6262

Roles of Intestinal Juice & Brush-Border Roles of Intestinal Juice & Brush-Border EnzymesEnzymes

• Submucosal layer has duodenal glands Submucosal layer has duodenal glands – secretes alkaline mucussecretes alkaline mucus

• Mucosal layer contains intestinal glands = Mucosal layer contains intestinal glands = Crypts of Lieberkuhn(deep to surface)Crypts of Lieberkuhn(deep to surface)– secretes intestinal juice secretes intestinal juice

• 1-2 qt./day------ at pH 7.61-2 qt./day------ at pH 7.6

– brush border enzymesbrush border enzymes– paneth cells secrete lysozyme kills bacteriapaneth cells secrete lysozyme kills bacteria

6363

Mechanical Digestion in the Small Mechanical Digestion in the Small IntestineIntestine

• Weak peristalsis in Weak peristalsis in comparison to the comparison to the stomach---chyme stomach---chyme remains for 3 to 5 remains for 3 to 5 hourshours

• Segmentation---local Segmentation---local mixing of chyme with mixing of chyme with intestinal juices---intestinal juices---sloshing back & forthsloshing back & forth

6464

Digestion of Digestion of CarbohydratesCarbohydrates

• Mouth---salivary amylaseMouth---salivary amylase

• Esophagus & stomach---nothing Esophagus & stomach---nothing happenshappens

• Duodenum----pancreatic amylaseDuodenum----pancreatic amylase

• Brush border enzymes (maltase, Brush border enzymes (maltase, sucrase & lactose) act on sucrase & lactose) act on disaccharidesdisaccharides– produces monosaccharides--fructose, produces monosaccharides--fructose,

glucose & galactoseglucose & galactose– lactose intolerance (no enzyme; bacteria lactose intolerance (no enzyme; bacteria

ferment sugar)--gas & diarrheaferment sugar)--gas & diarrhea

6565

Lactose IntoleranceLactose Intolerance• Mucosal cells of small intestine fail to Mucosal cells of small intestine fail to

produce lactaseproduce lactase– essential for digestion of lactose sugar in essential for digestion of lactose sugar in

milkmilk– undigested lactose retains fluid in the fecesundigested lactose retains fluid in the feces– bacterial fermentation produces gasesbacterial fermentation produces gases

• SymptomsSymptoms– diarrhea, gas, bloating & abdominal crampsdiarrhea, gas, bloating & abdominal cramps

• Dietary supplements are helpfulDietary supplements are helpful

6666

Digestion of Digestion of ProteinsProteins

• StomachStomach– HCl denatures or unfolds proteinsHCl denatures or unfolds proteins– pepsin turns proteins into peptidespepsin turns proteins into peptides

• PancreasPancreas– digestive enzymes---split peptide bonds digestive enzymes---split peptide bonds

between different amino acidsbetween different amino acids– brush border enzymes-----aminopeptidase brush border enzymes-----aminopeptidase

or dipeptidase------split off amino acid at or dipeptidase------split off amino acid at amino end of molecule or split dipeptideamino end of molecule or split dipeptide

6767

Digestion of Digestion of LipidsLipids

• Mouth----lingual lipaseMouth----lingual lipase

• Small intestineSmall intestine– emulsification by bileemulsification by bile– pancreatic lipase---splits into fatty pancreatic lipase---splits into fatty

acids & monoglycerideacids & monoglyceride– no enzymes in brush borderno enzymes in brush border

6868

Digestion of Nucleic AcidsDigestion of Nucleic Acids

• Pancreatic juice contains 2 Pancreatic juice contains 2 nucleasesnucleases– ribonuclease which digests RNAribonuclease which digests RNA– deoxyribonuclease which digests DNAdeoxyribonuclease which digests DNA

• Absorbed by active transportAbsorbed by active transport

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Absorption in Small Absorption in Small IntestineIntestine

7070

Where will the absorbed nutrients Where will the absorbed nutrients go?go?

7171

Absorption of Absorption of Lipids Lipids • Small fatty acids enter cells & then blood by simple Small fatty acids enter cells & then blood by simple

diffusiondiffusion

• Lipids enter cells by simple diffusion leaving bile salts Lipids enter cells by simple diffusion leaving bile salts behind in gut behind in gut

• were within micelleswere within micelles

7272

Absorption of Absorption of ElectrolytesElectrolytes• Sources of electrolytesSources of electrolytes

– GI secretions & ingested foods and liquids GI secretions & ingested foods and liquids

• Enter epithelial cells by diffusion & secondary Enter epithelial cells by diffusion & secondary active transportactive transport– sodium & potassium move = Na+/K+ pumps sodium & potassium move = Na+/K+ pumps

(active transport)(active transport)– chloride, iodide and nitrate = passively followchloride, iodide and nitrate = passively follow– iron, magnesium & phosphate ions = active iron, magnesium & phosphate ions = active

transporttransport

• Intestinal Ca+ absorption requires vitamin D & Intestinal Ca+ absorption requires vitamin D & parathyroid hormoneparathyroid hormone

7373

Absorption of Absorption of VitaminsVitamins

• Fat-soluble vitamins Fat-soluble vitamins – travel in micelles & are absorbed by travel in micelles & are absorbed by

simple diffusionsimple diffusion

• Water-soluble vitaminsWater-soluble vitamins– absorbed by diffusionabsorbed by diffusion

• B12 combines with intrinsic factor B12 combines with intrinsic factor before it is transported into the cellsbefore it is transported into the cells– receptor mediated endocytosisreceptor mediated endocytosis

7474

Absorption of WAbsorption of Waterater • 9 liters of fluid dumped 9 liters of fluid dumped

into GI tract each dayinto GI tract each day

• Small intestine Small intestine reabsorbs 8 litersreabsorbs 8 liters

• Large intestine Large intestine reabsorbs 90% of that reabsorbs 90% of that last literlast liter

• Absorption is by Absorption is by osmosis through cell osmosis through cell walls into vascular walls into vascular capillaries inside villicapillaries inside villi

7575

Anatomy of Large Anatomy of Large IntestineIntestine

• 5 feet long by 2½ inches in diameter5 feet long by 2½ inches in diameter• Ascending & descending colon are retroperitonealAscending & descending colon are retroperitoneal• Cecum & appendixCecum & appendix

• Rectum = last 8 inches of GI tract anterior to the sacrum & coccyxRectum = last 8 inches of GI tract anterior to the sacrum & coccyx• Anal canal = last 1 inch of GI tractAnal canal = last 1 inch of GI tract

– internal sphincter----smooth muscle & involuntary internal sphincter----smooth muscle & involuntary – external sphincter----skeletal muscle & voluntary controlexternal sphincter----skeletal muscle & voluntary control

7676

AppendicitisAppendicitis• Inflammation of the appendix due to Inflammation of the appendix due to

blockage of the lumen by chyme, blockage of the lumen by chyme, foreign body, carcinoma, stenosis, or foreign body, carcinoma, stenosis, or kinking kinking

• SymptomsSymptoms– high fever, elevated WBC count, neutrophil high fever, elevated WBC count, neutrophil

count above 75%count above 75%– referred pain, anorexia, nausea and referred pain, anorexia, nausea and

vomitingvomiting– pain localizes in right lower quadrantpain localizes in right lower quadrant

• Infection may progress to gangrene and Infection may progress to gangrene and perforation within 24 to 36 hoursperforation within 24 to 36 hours

7777

Histology of Large IntestineHistology of Large Intestine

• Muscular layerMuscular layer– internal circular layer is normalinternal circular layer is normal– outer longitudinal muscleouter longitudinal muscle

• taeniae coli = shorter bandstaeniae coli = shorter bands• haustra (pouches) formedhaustra (pouches) formed• epiploic appendages epiploic appendages

• Serosa = visceral peritoneumSerosa = visceral peritoneum

• AppendixAppendix– contains large amounts of contains large amounts of

lymphatic tissuelymphatic tissue

7878

Mechanical Digestion in Large Mechanical Digestion in Large IntestineIntestine

• Smooth muscle = mechanical digestionSmooth muscle = mechanical digestion• Peristaltic waves Peristaltic waves (3 to 12 contractions/minute)(3 to 12 contractions/minute)

– haustral churning----relaxed pouches are filled haustral churning----relaxed pouches are filled from below by muscular contractions from below by muscular contractions (elevator)(elevator)

– gastroilial reflex = when stomach is full, gastroilial reflex = when stomach is full, gastrin hormone relaxes ileocecal sphincter so gastrin hormone relaxes ileocecal sphincter so small intestine will empty and make roomsmall intestine will empty and make room

– gastrocolic reflex = when stomach fills, a gastrocolic reflex = when stomach fills, a strong peristaltic wave moves contents of strong peristaltic wave moves contents of transverse colon into rectumtransverse colon into rectum

7979

Chemical Digestion in Large Chemical Digestion in Large IntestineIntestine

• No enzymes are secreted only No enzymes are secreted only mucousmucous

• Bacteria fermentBacteria ferment– undigested carbohydrates into carbon undigested carbohydrates into carbon

dioxide & methane gasdioxide & methane gas– undigested proteins into simpler undigested proteins into simpler

substances (indoles)----odorsubstances (indoles)----odor– turn bilirubin into simpler substances turn bilirubin into simpler substances

that produce colorthat produce color

• Bacteria produce vitamin K and B in Bacteria produce vitamin K and B in coloncolon

8080

Absorption & Feces Absorption & Feces Formation in the Large Formation in the Large IntestineIntestine• Some electrolytes---Na+ and Cl- Some electrolytes---Na+ and Cl-

• After 3 to 10 hours, 90% of H2O has After 3 to 10 hours, 90% of H2O has been removed from chymebeen removed from chyme

• Feces are semisolid by time reaches Feces are semisolid by time reaches transverse colontransverse colon

• Feces = dead epithelial cells, Feces = dead epithelial cells, undigested food such as cellulose, undigested food such as cellulose, bacteria (live & dead)bacteria (live & dead)

8181

Defecation Defecation • Gastrocolic reflex moves Gastrocolic reflex moves

feces into rectumfeces into rectum

• Stretch receptors signal Stretch receptors signal sacral spinal cordsacral spinal cord

• Parasympathetic nerves Parasympathetic nerves contract muscles of contract muscles of rectum & relax internal rectum & relax internal anal sphincteranal sphincter

• External sphincter is External sphincter is voluntarily controlledvoluntarily controlled

8282

Defecation ProblemsDefecation Problems

• Diarrhea = chyme passes too quickly Diarrhea = chyme passes too quickly through intestine through intestine – HH220 not reabsorbed0 not reabsorbed

• Constipation--decreased intestinal Constipation--decreased intestinal motilitymotility– too much water is reabsorbedtoo much water is reabsorbed– remedy = fiber, exercise and waterremedy = fiber, exercise and water

8383

Dietary FiberDietary Fiber• Insoluble fiberInsoluble fiber

– woody parts of plants (wheat bran, vegie woody parts of plants (wheat bran, vegie skins)skins)

– speeds up transit time & reduces colon speeds up transit time & reduces colon cancercancer

• Soluble fiberSoluble fiber– gel-like consistency = beans, oats, citrus gel-like consistency = beans, oats, citrus

white parts, appleswhite parts, apples– lowers blood cholesterol by preventing lowers blood cholesterol by preventing

reabsorption of bile salts so liver has to use reabsorption of bile salts so liver has to use cholesterol to make morecholesterol to make more

8484

Aging and the Digestive Aging and the Digestive SystemSystem• Changes that occurChanges that occur

– decreased secretory mechanismsdecreased secretory mechanisms– decreased motilitydecreased motility– loss of strength & tone of muscular tissueloss of strength & tone of muscular tissue– changes in neurosensory feedbackchanges in neurosensory feedback– diminished response to pain & internal stimulidiminished response to pain & internal stimuli

• SymptomsSymptoms– sores, loss of taste, peridontal disease, difficulty sores, loss of taste, peridontal disease, difficulty

swallowing, hernia, gastritis, ulcers, swallowing, hernia, gastritis, ulcers, malabsorption, jaundice, cirrhosis, pancreatitis, malabsorption, jaundice, cirrhosis, pancreatitis, hemorrhoids and constipationhemorrhoids and constipation

• Cancer of the colon or rectum is commonCancer of the colon or rectum is common

8585

Diseases of the GI TractDiseases of the GI Tract

• Dental caries and periodontal disease Dental caries and periodontal disease

• Peptic UlcersPeptic Ulcers

• DiverticulitisDiverticulitis

• Colorectal cancerColorectal cancer

• HepatitisHepatitis

• Anorexia nervosaAnorexia nervosa