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Digestive SystemDigestive System
http://www.hhmi.org/biointerhttp://www.hhmi.org/biointeractive/media/fate_of_fat-lg.moactive/media/fate_of_fat-lg.movv
Histology of Digestive Histology of Digestive TractTract
Epithelial layer is stratified Epithelial layer is stratified squamous in mouth, squamous in mouth, esophagus, and anal canal – esophagus, and anal canal – protectionprotection
Stomach and intestines are Stomach and intestines are lined by simple columnar lined by simple columnar epithelium – secretion and epithelium – secretion and absorptionabsorption
DigestionDigestion Digestion breaks food Digestion breaks food into small molecules into small molecules to facilitate to facilitate absorptionabsorptionChemical and Chemical and MechanicalMechanical
Aided by enzymesAided by enzymes
EnzymesEnzymesSpeed up chemical Speed up chemical reactions in the bodyreactions in the body
Proteins, usually ends in -Proteins, usually ends in -asease
Convert substrate to Convert substrate to product without being product without being changedchanged
http://programs.northlandcollege.edu/bhttp://programs.northlandcollege.edu/biology/Biology1111/animations/enzyme.iology/Biology1111/animations/enzyme.swfswf
Digestion in the MouthDigestion in the Mouth Mechanical digestion (mastication Mechanical digestion (mastication
or chewing)or chewing) Chemical digestionChemical digestion
Salivary amylaseSalivary amylasebegins starch digestion at pH of 6.5 or begins starch digestion at pH of 6.5 or 7.0 7.0
swallowed too quickly for all starches to swallowed too quickly for all starches to break down; Continues to digest for break down; Continues to digest for another hour; Stomach acid inactivatesanother hour; Stomach acid inactivates
Substrate – starchSubstrate – starchProduct - maltoseProduct - maltose
Composition and Functions Composition and Functions of Salivaof Saliva
99.5% water and 0.5% solutes99.5% water and 0.5% solutesBicarbonate ions buffer acidic Bicarbonate ions buffer acidic
foods (pH 6.35-6.85)foods (pH 6.35-6.85)Chemical digestion of starch Chemical digestion of starch
begins with enzyme (salivary begins with enzyme (salivary amylase)amylase)
Mucus lubricates foodMucus lubricates foodEnzyme (lysozyme) ---helps Enzyme (lysozyme) ---helps
destroy bacteriadestroy bacteria
Structure and Function of Structure and Function of the Tonguethe Tongue
Muscles move tongue to assist Muscles move tongue to assist in chewing and swallowingin chewing and swallowing
Papillae are the bumps---taste Papillae are the bumps---taste budsbuds
Lingual glands secrete mucus Lingual glands secrete mucus and serous fluid with enzyme and serous fluid with enzyme lipaselipase
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 32 teeth that erupt between 6 and 12
years of ageyears of age incisors for biting, canines for tearing, incisors for biting, canines for tearing,
premolars & molars for crushing and premolars & molars for crushing and grinding foodgrinding food
Often not enough room for third molars Often not enough room for third molars (wisdom teeth)(wisdom teeth)
EsophagusEsophagus
Collapsible muscular tube, Collapsible muscular tube, passagewaypassageway
10 inches long10 inches long Anterior to vertebraeAnterior to vertebrae Posterior to tracheaPosterior to trachea Posterior to the heart Posterior to the heart Pierces the diaphragm at hiatusPierces the diaphragm at hiatus
hiatal herniahiatal hernia
DisordersDisorders
Achalasia – lower esophageal Achalasia – lower esophageal sphincter fails to relax, meal sphincter fails to relax, meal stuck in esophagusstuck in esophagus
Heartburn – lower esophageal Heartburn – lower esophageal sphincter fails to close after sphincter fails to close after food enters stomachfood enters stomach
Stomach--MStomach--Mechanical echanical DigestionDigestion
peristaltic movements called peristaltic movements called mixing waves.mixing waves.
Pyloric sphincter remains Pyloric sphincter remains almost, but not completely, almost, but not completely, closedclosed
Gastric emptying – about 3mL Gastric emptying – about 3mL of chyme is forced outof chyme is forced out
Most chyme is forced back Most chyme is forced back into body of stomach to into body of stomach to continue mixingcontinue mixing
Stomach--Chemical Stomach--Chemical DigestionDigestionSalivary amylase continues to Salivary amylase continues to
workworkSecretion of HCl inactivates Secretion of HCl inactivates
amylase, activates lingual lipase amylase, activates lingual lipase and pepsinogen, kills microbes, and pepsinogen, kills microbes, and stimulates secretion of and stimulates secretion of hormones that promote bile and hormones that promote bile and pancreatic juicepancreatic juice
Protein digestionProtein digestionFat digestionFat digestion
Absorption in the StomachAbsorption in the Stomach Epithelial cells are impermeable to Epithelial cells are impermeable to
most materialsmost materials Water Water ElectrolytesElectrolytes Short-chain fatty acidsShort-chain fatty acids Some drugs (especially aspirin) & Some drugs (especially aspirin) &
alcoholalcohol Gastric mucosal cells contain alcohol Gastric mucosal cells contain alcohol
dehydrogenase that converts some dehydrogenase that converts some alcohol to acetaldehyde-----more of this alcohol to acetaldehyde-----more of this enzyme found in males than femalesenzyme found in males than females
Anatomy of StomachAnatomy of Stomach
Stomach LiningStomach Lining
DisordersDisorders
Peptic ulcer DiseasePeptic ulcer DiseaseH. pylori bacteriumH. pylori bacteriumPain relieversPain relieversHypersecretion of HClHypersecretion of HCl
Composition and Functions Composition and Functions of Pancreatic Juiceof Pancreatic Juice
1 & 1/2 Quarts/day at pH of 7.1 to 1 & 1/2 Quarts/day at pH of 7.1 to 8.28.2
Contains water, enzymes & sodium Contains water, enzymes & sodium bicarbonatebicarbonate
Digestive enzymesDigestive enzymespancreatic amylase and pancreatic pancreatic amylase and pancreatic
lipaselipasePancreatic nucleasesPancreatic nucleasesPancreatic trypsin (protease)Pancreatic trypsin (protease)
Histology of the Histology of the PancreasPancreasAciniAcini
Exocrine Exocrine 99% of 99% of glandgland
Islets of Islets of LangerhansLangerhansEndocrine Endocrine 1% of gland1% of gland
Bile ProductionBile Production One quart of bile/day is produced by One quart of bile/day is produced by
the liverthe liver yellow-green in color & pH 7.6 to 8.6yellow-green in color & pH 7.6 to 8.6
ComponentsComponents Water, cholesterol, bile salts, bile Water, cholesterol, bile salts, bile
pigments (bilirubin) from hemoglobin pigments (bilirubin) from hemoglobin molecule molecule
FunctionsFunctions Emulsification Emulsification
Produced by hepatocytes in liver, Produced by hepatocytes in liver, stored in gallbladderstored in gallbladder
Anatomy of the Small Anatomy of the Small IntestineIntestine
Major events of digestion Major events of digestion and absorption occur in and absorption occur in small intestinesmall intestine
Large surface areaLarge surface area 3 parts3 parts
duodenum---10 inchesduodenum---10 inches jejunum---8 feetjejunum---8 feet ileum---12 feetileum---12 feet
Small diameterSmall diameter
Histology of Small Histology of Small IntestineIntestine
Cells of Intestinal Cells of Intestinal GlandsGlands
Chemical Digestion in Small Chemical Digestion in Small IntestineIntestine
Chyme entering small intestine Chyme entering small intestine contains partially digested contains partially digested carbohydrates, proteins, and carbohydrates, proteins, and lipidslipids
The completion of the digestion The completion of the digestion is a collective effort of pancreatic is a collective effort of pancreatic juice, bile, and intestinal juice in juice, bile, and intestinal juice in the small intestinethe small intestine
Occurs in duodenumOccurs in duodenum
Review: Digestion of Review: Digestion of CarbohydratesCarbohydrates Mouth---salivary amylaseMouth---salivary amylase
Duodenum----pancreatic amylaseDuodenum----pancreatic amylase Brush border enzymes (maltase, Brush border enzymes (maltase,
sucrase & lactase) act on sucrase & lactase) act on disaccharidesdisaccharidesproduces monosaccharides--fructose, produces monosaccharides--fructose,
glucose & galactoseglucose & galactose lactose intolerance (no enzyme; lactose intolerance (no enzyme;
bacteria ferment sugar)--gas & bacteria ferment sugar)--gas & diarrheadiarrhea
Review: Digestion of Review: Digestion of ProteinsProteins StomachStomach
HCl denatures or unfolds proteinsHCl denatures or unfolds proteinspepsin turns proteins into small pepsin turns proteins into small
polypeptidespolypeptides PancreasPancreas
Pancreatic trypsin--split peptide Pancreatic trypsin--split peptide bonds between amino acidsbonds between amino acids
brush border enzymes-----brush border enzymes-----aminopeptidase or dipeptidaseaminopeptidase or dipeptidase
Review: Digestion of Review: Digestion of LipidsLipids
Mouth----lingual lipaseMouth----lingual lipaseMost lipid digestion, in an Most lipid digestion, in an adult, occurs in the small adult, occurs in the small intestine.intestine.emulsification by bile emulsification by bile pancreatic lipase---splits pancreatic lipase---splits triglycerides into fatty acids & triglycerides into fatty acids & monoglyceridesmonoglycerides
Where will the absorbed Where will the absorbed nutrients go?nutrients go?
Anatomy of Large IntestineAnatomy of Large Intestine5 feet long by 2½ inches in 5 feet long by 2½ inches in
diameterdiameter
DisordersDisorders
Appendicitis – Appendicitis – inflammation of appendixinflammation of appendixDue to blockage or Due to blockage or bacterial infectionbacterial infection
Can rupture and spread to Can rupture and spread to abdomenabdomen
Histology of Large IntestineHistology of Large Intestine MucosaMucosa
smooth tube -----no smooth tube -----no villi or plicavilli or plica
Micro-villi of Micro-villi of absorptive cells are absorptive cells are presentpresent
simple columnar simple columnar cells absorb water & cells absorb water & goblet cells secrete goblet cells secrete mucusmucus
Digestion in Large IntestineDigestion in Large Intestine Mechanical digestion includes Mechanical digestion includes
peristalsisperistalsis Chemical digestion - bacteriaChemical digestion - bacteria
undigested carbohydrates into carbon undigested carbohydrates into carbon dioxide & methane gasdioxide & methane gas
undigested proteins into simpler undigested proteins into simpler substances (odor)substances (odor)
turn bilirubin into simpler substances that turn bilirubin into simpler substances that produce colorproduce color
Bacteria produce vitamin K and B in colonBacteria produce vitamin K and B in colon
Absorption & Feces Absorption & Feces Formation Formation
Some electrolytes (Na+ and Cl-) and Some electrolytes (Na+ and Cl-) and vitamins vitamins
After 3 to 10 hours, Feces are semisolid After 3 to 10 hours, Feces are semisolid Feces = dead epithelial cells, undigested Feces = dead epithelial cells, undigested
food such as cellulose, bacteria (live & food such as cellulose, bacteria (live & dead)dead)
90% of H2O has been removed from 90% of H2O has been removed from chyme in small intestine, but large chyme in small intestine, but large intestine absorbs enough water to make intestine absorbs enough water to make it important in maintaining water balanceit important in maintaining water balance
Absorption of WAbsorption of Waterater 9 liters of fluid 9 liters of fluid
dumped into GI dumped into GI tract each daytract each day
Small intestine Small intestine reabsorbs 8 litersreabsorbs 8 liters
Large intestine Large intestine reabsorbs 90% of reabsorbs 90% of that last literthat last liter
TimingTiming
After food is chewed and swallowed After food is chewed and swallowed – 5-10 seconds to pass down – 5-10 seconds to pass down esophagus to stomachesophagus to stomach
Partial digestion in stomach – 2-6 Partial digestion in stomach – 2-6 hourshours
Final digestion and absorption in Final digestion and absorption in small intestine – 5-6 hourssmall intestine – 5-6 hours
In 12-24 hours undigested material In 12-24 hours undigested material passes through large intestinepasses through large intestine