1 Chapter 24 Chapter 24 The Digestive System The Digestive System • Structure Structure – Gross Gross Anatomy Anatomy – Histology Histology • Function Function – Mechanical Mechanical – Chemical Chemical • Development Development • Disorders Disorders
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1 Chapter 24 The Digestive System Structure Structure –Gross Anatomy –Histology Function Function –Mechanical –Chemical Development Development Disorders.
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Chapter 24Chapter 24The Digestive SystemThe Digestive System
• 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
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SubmucosaSubmucosa
• Loose connective tissueLoose connective tissue– containing BV, glands and lymphatic tissuecontaining BV, glands and lymphatic tissue
fibersfibers– mixes, crushes & propels food along by mixes, crushes & propels food along by
peristalsisperistalsis
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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
• Peritoneal cavityPeritoneal cavity– potential space potential space
containing a bit of containing a bit of serous fluidserous fluid
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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
• 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
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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
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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)
• 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
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
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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
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Composition of TeethComposition of Teeth• EnamelEnamel
– hardest substance in hardest substance in bodybody
– calcium phosphate or calcium phosphate or carbonatecarbonate
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
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Primary and Secondary Primary and Secondary DentitionDentition
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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
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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
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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
• Adventitia = connective tissue blending Adventitia = connective tissue blending with surrounding connective tissue--no with surrounding connective tissue--no peritoneumperitoneum
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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
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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
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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
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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
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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
• 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
• 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
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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
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Absorption of Nutrients by the Absorption of Nutrients by the StomachStomach• Water especially if it is coldWater especially if it is cold
• 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
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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
– 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
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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
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
• 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
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
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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
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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
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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
• 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
• 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
• 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)
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Summary of Digestive Summary of Digestive HormonesHormones• GastrinGastrin
Histology of Small IntestineHistology of Small Intestine
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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
– 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
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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
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
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Digestion of Digestion of CarbohydratesCarbohydrates
• 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
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
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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
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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
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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
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
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Histology of Large IntestineHistology of Large Intestine
• Muscular layerMuscular layer– internal circular layer is normalinternal circular layer is normal– outer longitudinal muscleouter longitudinal muscle
– 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
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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
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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)
• 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
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