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Physiology 1Physiology 1

The Gastrointestinal TractThe Gastrointestinal Tract

Guyton section XI

Overview Overview

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Basic functions of the GI tractBasic functions of the GI tract

DigestionDigestionSecretion Secretion Absorption Absorption MotilityMotility

Basic functions of the GI tractBasic functions of the GI tract

DigestionDigestion: Dissolving and breaking down : Dissolving and breaking down ingested particlesingested particles

Basic functions of the GI tractBasic functions of the GI tract

Digestion: Dissolving and breaking down Digestion: Dissolving and breaking down ingested particlesingested particlesSecretionSecretion: Releasing enzymes, bile and : Releasing enzymes, bile and Hydrochloric acid into the lumen of the GI tractHydrochloric acid into the lumen of the GI tract

Basic functions of the GI tractBasic functions of the GI tract

Digestion: Dissolving and breaking down Digestion: Dissolving and breaking down ingested particlesingested particlesSecretion: Releasing enzymes, bile and Secretion: Releasing enzymes, bile and Hydrochloric acid into the lumen of the GI tractHydrochloric acid into the lumen of the GI tractAbsorptionAbsorption: Moving molecules from the lumen : Moving molecules from the lumen into the blood or lymph into the blood or lymph

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Basic functions of the GI tractBasic functions of the GI tract

Digestion: Dissolving and breaking down Digestion: Dissolving and breaking down ingested particlesingested particlesSecretion: Releasing enzymes, bile and Secretion: Releasing enzymes, bile and Hydrochloric acid into the lumen of the GI tractHydrochloric acid into the lumen of the GI tractAbsorption: Moving molecules from the lumen Absorption: Moving molecules from the lumen into the blood or lymph into the blood or lymph MotilityMotility: Moving food through the GI Tract: Moving food through the GI Tract

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Structure of the Gastrointestinal Structure of the Gastrointestinal Tract Wall Tract Wall

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Digestion and Absorption of Digestion and Absorption of nutrientsnutrients

CarbohydrateCarbohydrateProteinProteinFatFat

Digestion and Absorption of Digestion and Absorption of nutrientsnutrients

Carbohydrate: Carbohydrate: Body only absorbs Body only absorbs monosaccaridesmonosaccarides (glucose, (glucose, fructose, fructose, galactosegalactose))Enzymes on luminal membrane break down Enzymes on luminal membrane break down complex sugars into complex sugars into monosacaridesmonosacaridesMonosaccaridesMonosaccarides enter body by facilitated enter body by facilitated difussiondifussionCellulose (fiber) can not be broken downCellulose (fiber) can not be broken down

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Digestion and Absorption of Digestion and Absorption of nutrientsnutrients

Protein: Free amino acids and short chains can Protein: Free amino acids and short chains can be absorbed.be absorbed.Enzymes Enzymes

Stomach (pepsin)Stomach (pepsin)Small intestine (Small intestine (chymotrypsinchymotrypsin, , TrypsinTrypsin))Pancreas (Pancreas (CarboxypepsidaseCarboxypepsidase))Small intestine epithelium (Small intestine epithelium (AminopepsidaseAminopepsidase))

Digestion and Absorption of Digestion and Absorption of nutrientsnutrients

CarbohydrateCarbohydrateProteinProteinFat: must be Emulsified in lumen before Fat: must be Emulsified in lumen before absorbedabsorbed

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Structure of Bile SaltsStructure of Bile SaltsEmulsification Emulsification

of Fatof Fat

Fat Digestion/ LipaseFat Digestion/ Lipase

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Following the pathway of ingested Following the pathway of ingested foodfood

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Secretions from the StomachSecretions from the Stomach

Parietal cells Parietal cells –– secrete acidsecrete acidChief cells Chief cells –– secrete secrete pepsinogenpepsinogenEnterochromaffinEnterochromaffin-- like cells like cells –– release histamine release histamine into the bodyinto the body

Conversion of Conversion of PepsinogenPepsinogen to Pepsinto Pepsin

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Regulation of stomach acid secretionRegulation of stomach acid secretion

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Small intestineSmall intestine

DuodenumDuodenumJejunumJejunumIleumIleum

LiverLiver

Produces BileProduces BileBile pigments (Bile pigments (bilirubinbilirubin))

Has Has enterohepaticenterohepatic circulationcirculation

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Secretion of Bile is regulated by the Secretion of Bile is regulated by the hormone hormone CholecystokininCholecystokinin (CCK)(CCK)

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PancreasPancreas

Secretes Bicarbonate to neutralize stomach acidSecretes Bicarbonate to neutralize stomach acidSecretes digestive enzymesSecretes digestive enzymes

TrypsinTrypsin

Regulates whole body metabolism viaRegulates whole body metabolism viaInsulinInsulinGlucagonGlucagonSomatostatinSomatostatin

Structure of the pancreasStructure of the pancreas

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Regulation of the PancreasRegulation of the Pancreas

Acid levels in Small Intestine stimulate Acid levels in Small Intestine stimulate pancreatic bicarbonate release (via pancreatic bicarbonate release (via SecretinSecretin))Amino and Fatty acids stimulate enzyme release Amino and Fatty acids stimulate enzyme release (via (via CholecystokininCholecystokinin, CCK), CCK)

Small intestineSmall intestine

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Movement of the Small IntestineMovement of the Small Intestine

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Physiology 12Physiology 12

Regulation of systemic MetabolismRegulation of systemic Metabolism

Germann Ch 20

Feast or FamineFeast or Famine

Everyday the body must shift its Everyday the body must shift its metabolismmetabolism

In the fed (absorptive) stateIn the fed (absorptive) state

Food is being digested or absorbedFood is being digested or absorbedEnergy comes primarily from carbohydratesEnergy comes primarily from carbohydrates

In the fed (absorptive) stateIn the fed (absorptive) state

Food is being digested or absorbedFood is being digested or absorbedEnergy comes primarily from carbohydratesEnergy comes primarily from carbohydratesExtra carbohydrates are converted to fat (via Extra carbohydrates are converted to fat (via liver glycogen production)liver glycogen production)

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In the fed (absorptive) stateIn the fed (absorptive) state

Food is being digested or absorbedFood is being digested or absorbedEnergy comes primarily from carbohydratesEnergy comes primarily from carbohydratesExtra carbohydrates are converted to fat (via Extra carbohydrates are converted to fat (via liver glycogen production)liver glycogen production)Ingested fatty acids are stored in adiposeIngested fatty acids are stored in adipose

In the fed (absorptive) stateIn the fed (absorptive) state

Food is being digested or absorbedFood is being digested or absorbedEnergy comes primarily from carbohydratesEnergy comes primarily from carbohydratesExtra carbohydrates are converted to fat (via Extra carbohydrates are converted to fat (via liver glycogen production)liver glycogen production)Ingested fatty acids are stored in adiposeIngested fatty acids are stored in adiposeExcess amino acids are converted to FatExcess amino acids are converted to Fat

In the Fasted (In the Fasted (postabsorptivepostabsorptive) state) state

Glycogen and fat production stopsGlycogen and fat production stops

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In the Fasted (In the Fasted (postabsorptivepostabsorptive) state) state

Glycogen and fat production stopsGlycogen and fat production stopsLiver releases glucose to maintain blood Liver releases glucose to maintain blood Glucose levelsGlucose levels

(brain must have glucose)(brain must have glucose)

In the Fasted (In the Fasted (postabsorptivepostabsorptive) state) state

Glycogen and fat production stopsGlycogen and fat production stopsLiver releases glucose to maintain blood Liver releases glucose to maintain blood Glucose levelsGlucose levels

(brain must have glucose)(brain must have glucose)

Most energy comes from Fatty acids and Most energy comes from Fatty acids and KeytonesKeytones

In the Fasted (In the Fasted (postabsorptivepostabsorptive) state) state

Glycogen and fat production stopsGlycogen and fat production stopsLiver releases glucose to maintain blood Liver releases glucose to maintain blood Glucose levelsGlucose levels

(brain must have glucose)(brain must have glucose)

Most energy comes from Fatty acids and Most energy comes from Fatty acids and KeytonesKeytonesMuscle breaks down Muscle glycogen for fuel.Muscle breaks down Muscle glycogen for fuel.

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Feast or famine states are regulated Feast or famine states are regulated by Pancreatic hormones by Pancreatic hormones

InsulinInsulinGlucagonGlucagon

The endocrine PancreasThe endocrine Pancreas

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Islet of Islet of LangerhansLangerhans

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Insulin is produced by the Pancreatic Insulin is produced by the Pancreatic islet beta cells,islet beta cells,

its release is regulatedits release is regulatedCirculating glucoseCirculating glucoseCirculating amino acidsCirculating amino acidsSympathetic/parasympathetic nervesSympathetic/parasympathetic nervesOther gut hormones (GIP)Other gut hormones (GIP)

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GlucagonGlucagon

Secreted from the pancreatic islet alpha cells Secreted from the pancreatic islet alpha cells Stimulated by drops in blood sugarStimulated by drops in blood sugar

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Whole body Whole body metabolismmetabolism

Metabolic RateMetabolic Rate

Total energy expenditure per unit timeTotal energy expenditure per unit timeMeasured in KilocaloriesMeasured in KilocaloriesVaries with activities and inputsVaries with activities and inputs

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Total regulation of metabolism is a Total regulation of metabolism is a balanced equationbalanced equation

Food ingested = total energy expendedFood ingested = total energy expended

Total energy expenditure = Total energy expenditure = Work + Heat produced + energy Work + Heat produced + energy

storedstored

Factors affecting Metabolic rateFactors affecting Metabolic rate

EpinephrineEpinephrineFoodFoodMuscle activityMuscle activityBrown adipose tissue activity Brown adipose tissue activity HormonesHormones

Hormones affecting MetabolismHormones affecting Metabolism

ThyroidThyroidThyroxineThyroxine

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ThyroxineThyroxine

Hormones affecting MetabolismHormones affecting Metabolism

ThyroidThyroidThyroxineThyroxine

Adrenal cortical Adrenal cortical hormonehormone

CortisolCortisol

Hormones affecting MetabolismHormones affecting Metabolism

ThyroidThyroidThyroxineThyroxine

Adrenal cortical hormoneAdrenal cortical hormoneCortisolCortisol

LeptinLeptin

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Hormonal Regulation of GrowthHormonal Regulation of Growth

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