Digestive SystemDigestive System

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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

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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