To accompany Anatomy and Physiology: The Digestive System

to accompany

Anatomy and Physiology:

The Digestive System

Overview

1 Gastrointestinal (GI) Tract2 Accessory Organs of the Head3 Swallowing4 Stomach5 Accessory Organs of the Abdomen6 Small Intestine7 Large Intestine8 Phases of Digestion 9 Food Molecules

Essential Termsdigestionprocess of mechanically or chemically

breaking down foodabsorptionpassage of small molecules into blood and

lymphdigestive systemorgans which carry out process of digestion

and absorptionmetabolismall the chemical reactions of the body

Introduction

Digestive System1. Composed of GI tract and accessory

organs2. Breaks down ingested food for use by

the body3. Digestion occurs by mechanical and

chemical mechanisms4. Excretes waste products or feces

through process of defecation

GI Tract / Alimentary CanalContinuous tube from mouth to anusMouthPharynxEsophagusStomachSmall intestineLarge intestine

Accessory Digestive OrgansProvide mechanical and chemical mechanisms to

aid digestionTeethTongueSalivary glandsLiverGallbladderPancreas

Functions of Digestive System1. Ingestion2. Secretion3. Mixing and propulsion

• Motility

4. Digestion• Mechanical and chemical

5. Absorption6. Defecation

Layers of GI TractSame in all areas of GI tract

From deep to superficial:MucosaSubmucosaMuscularisSerosa

Figure 23.2

Layers of GI TractMucosa

EpitheliumType varies

Lamina propria – areolar connective tissueMALT – mucus-associated lymphatic tissue

Muscularis mucosae – smooth muscleSubmucosa

Areolar connective tissueBlood and lymphatic vesselsNeurons – submucosal plexus

Layers of GI TractMuscularis

Skeletal and smooth muscleNeurons – myenteric plexus

SerosaAreolar and simple squamous epitheliumVisceral peritoneum

PeritoneumMesotheliumParietal peritoneumVisceral peritoneumPeritoneal cavityRetroperitoneal

Figure 23.3a

Figure 23.3b

Figure 23.3c

Figure 23.3d

Neural Innervation of GI Tract Regulated by autonomic nervous system

Enteric divisionMyenteric plexus / plexus of AuerbachSubmucosal plexus / plexus of Meissner

Able to function independently from rest of nervous system

Linked to CNS by extrinsic sympathetic and parasympathetic nerves

Sympathetic nerves decrease GI secretions & motility Parasympathetic nerves increase GI secretion and

motility

Mouth Parts of Digestive System

Mouth formed by several parts:

CheeksLips / labiaLabial frenulumOrbicularisVestibuleOral cavity properFaucesHard and soft palateUvulaPalatoglossal and palatopharyngeal arch

Figure 23.4

TongueSkeletal muscle and mucous membraneHelps form floor of oral cavityExtrinsic musclesIntrinsic musclesLingual frenulumPapillae

FungiformFiliformCircumvallateFoliate

Lingual glandsLingual lipase

Salivary GlandsRelease saliva to oral cavity

3 pairs of salivary glandsParotidSubmandibularSublingual

Composition of Saliva99.5 % water0.5% other solutes

IonsMucusImmunoglobulin AEnzymes

Salivation controlled by autonomic nervous system

Stimulated by various mechanisms

Figure 23.5

Teeth External regions

1. Crown2. Root3. Neck

Internal components1. Enamel2. Dentin

Cementum3. Pulp cavity

PulpRoot canals Apical foramen

Figure 23.6

TeethDentitionsDeciduous teeth – first setPermanent teeth – secondary

Carry out mechanical digestion by mastication

Creates bolus

Salivary amylaseBreakdown starchLingual lipaseBreakdown triglycerides

Figure 23.7

PharynxComposed of skeletal muscleLined by mucous membrane

NasopharynxOropharynxLaryngopharynx

EsophagusCollapsible muscular tube through

esophageal hiatus of diaphragm

MucosaSubmucosa contains areolar connective tissue

MuscularisSkeletal muscleUpper and lower esophageal sphincter

AdventitiaAttaches esophagus to nearby structures

Secrets mucus and transports food

Figure 23.8

DeglutitionStages of swallowingVoluntary

Mouth to oropharynxPharyngeal

Deglutition center in medulla oblongata and ponsClosing of epiglottisInvoluntary

EsophagealInvoluntaryPeristaltic contractions

Figure 23.9a,b

Figure 23.9c

Table 23.2

Stomach Serves as mixing chamber and storage

area for ingested food Rugae allow for increased volume 4 main regions1. Cardia2. Fundus3. Body4. Pylorus

Pyloric antrum and canal Pyloric sphincter Lesser and greater curvatures

Figure 23.10a

Stomach Histology1. Mucosa

Surface mucous cells Lamina propria Muscularis mucosae Gastric glands and pits Parietal cells Chief cells G cells

2. Submucosa – areolar connective tissue3. Muscularis

3 layers of smooth muscle

4. Serosa

Figure 23.11a

Figure 23.11b

Mechanical and Chemical Digestion

Mixing waves caused by peristaltic movementChyme released in process of gastric emptyingProton pumps bring H+ into the lumenCarbonic anhydrase forms carbonic acid to

provide H+ and bicarbonate ions (HCO3-)

Figure 23.12

Mechanical and Chemical Digestion

Chemical digestion stimulated by nervous system

Parasympathetic neurons release acetylcholineWorks with gastrinHCl released in presence of histamine

Pepsin begins digestion of proteinsStomach protected by alkaline mucus secretion

Gastric lipase digests triglyceridesFew molecules absorbed by stomach

Water, ions, short-chain fatty acids, alcohol

Table 23.3 pt 1

Table 23.3 pt 2

PancreasProduces secretions to aid digestion HeadBodyTailPancreatic duct /duct of Wirsung

Hepatopancreatic ampullaSphincter of the heatopancreatic ampulla

(sphincter of (Oddi)Regulates passage of pancreatic juice and bile

Accessory duct (duct of Santorini)

Figure 23.13a

Figure 23.13b

Figure 23.13c

Histology of PancreasGlandular epithelial cells

99% exocrine clustersSecrete pancreatic juice

Fluid and enzymesPancreatic islets (islets of Langerhans)

1% endocrine cellsHormones

GlucagonInsulinSomatostatin

Pancreatic polypeptide

Pancreatic Juice 1200-1500 mL/day pH 7.1-8.2 Water Salts Sodium bicarbonate Enzymes

Pancreatic amylaseTrypsin

EntereokinaseChymotrypsinCarboxypeptidaseElastasePancreatic lipaseRibonuclease and deoxyribonuclease

Liver and GallbladderLiverLargest gland at 1.4 kg (~3 lb)

GallbladderClosely associated with liver

Anatomy of LiverRight and left lobe separated by falciform

ligamentQuadrate lobeCaudate lobe

Round ligament (ligamentum teres)Remnant of umbilical vein

coronary ligaments

Histology of LiverLobule

Hepatocytes radiating from central veinSinusoids

Reticuloendothelial (Kupffer) cellsStationary phagocytes

Figure 23.14a

Figure 23.14b

Figure 23.14c

Figure 23.14d

Bile Duct SystemBile secreted by hepatocytesBile canaliculiBile ductsRight and left hepatic ductsCommon hepatic ductCommon bile duct

Gallbladder for temporary storage of bileCystic duct

Blood Supply of LiverHepatic artery provides oxygenated bloodHepatic portal vein provides deoxygenated

bloodNutrients, drugs, toxins, microbes

Hepatic artery and vein carry blood to sinusoidsSubstances exchanged by hepatocytesBlood drains to central vein and eventually hepatic

veinPortal triad

Hepatic portal veinHepatic arteryBile duct

Figure 23.15

Bile800-1000 mL/daypH 7.6 – 8.6 WaterBile acidsBile salts

EmulsificationCholesterolLecithinBile pigments

BilirubinStercobilin

Liver Functions Metabolism of:

CarbohydratesLipidsProteins

Process drugs and hormones Excrete bilirubin Synthesize bile salts Storage

GlycogenVtaminsMinerals

Phagocytosis Activate Vitamin D

Small IntestineAdapted for digestion and absorption3 m (10 ft) living6.5 m (21 ft) without muscle tone

DuodenumJejunumIleum

Ileocecal sphincterConnection to large intestine

Figure 23.16a

Figure 23.16b

Histology of Small IntestineMucosaCell types

AbsorptiveGobletEndocrinePaneth

Lysozyme

Intestinal glands (crypts of Lieberkühn)S cells

Hormone secretinCCK cells

Hormone – cholecystokinin (CCK)

Figure 23.17a

Figure 23.17b

Histology of Small IntestineMALT – mucosa-associated lymphoid tissueSolitary lymphatic nodulesAggregated lymphatic follicles (Peyer’s patches)

SubmucosaDuodenal (Brunner’s glands)Alkaline secretion

MuscularisSerosa

Adaptive Structures Small IntestineCircular folds / plicae circularesVilliLacteal

Lymphatic capillaryMicrovilliBrush border

Brush border enzymesIntestinal juice

1-2 liters / daypH 7.6

Figure 23.18a

Figure 23.18b

Mechanical Digestion in Small Intestine

SegmentationLocalizedMix chyme with digestive juicesImportant for process of absorption

PeristalsisMovement along the length of small intestine

Chemical Digestion in Small Intestine

Completes digestion of food from the stomachCarbohydrates

Pancreatic amylaseGlycogen and starch only

-dextrinaseSucraseLactaseMaltase

Chemical Digestion in Small Intestine

ProteinsTrypsinChymotrypsinElastaseCarboxypeptidasePeptidases

Chemical Digestion in Small Intestine

LipidsPancreatic lipaseEmulsification

Amphipathic bile salts

Nucleic acidsNucleosidasesPhosphatases

Table 23.4 pt 1

Table 23.4 pt 2

Absorption in Small Intestine Passage of digested nutrients from gastointestinal

tract into blood or lymph 90% of nutrients absorbed through small intestine

Monosaccharides Facilitated diffusion

Fructose Secondary active transport

GlucoseGalactose

Enter blood through hepatic portal system

Absorption in Small IntestineAmino acids

Active transportNa+-dependent secondary active transport

Dipeptides and tripeptidesSymporter with H+

Absorption in Small IntestineLipids by simple diffusion

Due to emulsification and digestionMicelles formed due to amphipathic nature

of bile saltsChylomicrons

Triglycerides coated with proteinsLeave cells via exocytosisEnter blood vessels via lymphatic system

Enterohepatic circulation

Absorption in Small IntestineElectrolytes

DiffusionActive transportSecondary active transport

Vitamins

WaterOsmosis

Anatomy of Large Intestine Mesocolon attaches to posterior

abdominal wall

Regions1. Cecum2. Colon3. Rectum4. Anal canal

Ileocecal sphincter (valve) Allows passage into large intestine

Figure 23.21a

Figure 23.21b

Anatomy of Large Intestine1. Cecum

• Pouch• Attached appendix / veriform appendix

2. Colon• Ascending• Transverse• Descending• Sigmoid• Right and Left colic (splenic) flexures

3. Rectum4. Anal canal

• Anal columns• Anus• Internal and external sphincter

Histology of Large Intestine Mucosa

Absorptive cells absorb mainly waterGoblet cells secrete mucusLymphatic nodules

Submucosa Muscularis

HaustraExternal longitudinal smooth muscleTeniae coliInternal circular smooth muscle

SerosaEpiploic appendages

Figure 23.22a

Figure 23.22b

Figure 23.22c

Figure 23.22d

Mechanical digestion in Large Intestine

Gastroileal reflexIntensifies after a mealOccurs 3 or 4 times a day

Haustral churningDistension and contraction of haustra

PeristalsisMass peristalsis

Chemical Digestion in Large Intestine

Bacteria:Ferment carbohydrates

Gases produced are flatus or flatulence when excessive

Break down proteinsDecompose bilirubinFeces formed of dried chyme, inorganic salts,

mucus, bacteria, undigested foods and other substances

Defecation ReflexEmpties the rectumResponse to distention of rectal wallExternal anal sphincter voluntarily relaxed

defecation occurs

Table 23.7

Phases of DigestionCephalicGastricIntestinal

Cephalic PhaseStimulation of the senses activates CNSPrepares mouth and stomach for food

Phases of DigestionGastric PhaseBegins with food in the stomachNeural regulation

Negative feedback systemStretch receptorsChemoreceptors

Hormonal regulationGastrinReleased by G cells of gastric glandsControlled by negative feedback mechanism (pH)

Phases of DigestionIntestinal Phase

Begins with food in the small intestineInhibitory effects to slow exit of chyme

Neural regulationEnterogastric reflexDistension of duodenum

Phases of DigestionIntestinal Phase continued

Hormonal regulationCholecystokinin (CCK)

Stimulates release of pancreatic juiceContraction of gallbladder wallRelaxes sphincter of hepatopancreatic ampulla

SecretinResponse to acidic chymeStimulates flow of pancreatic juice for bufferingInhibits secretion of gastric juice

Table 23.8

Six Main Types of Nutrients1. Water2. Carbohydrates3. Lipids4. Proteins5. Minerals6. Vitamins

Essential nutrients cannot be made in sufficient amounts by the body

Guidelines for Healthy EatingVarietyMaintain healthy weightChoose low fat foodsLots of vegetables, fruits, and grainsSugar in moderationSalt and sodium in moderationAlcohol in moderation

Food Guide Pyramid

Figure 23.24

Nutrients Minerals

Inorganic elements constitute 4% of body massRegulate enzymatic reactionsServe as coenzymes

VitaminsOrganic molecules required in small amountsMost function as coenzymesMost cannot be synthesized by bodyProvitaminsFat-soluble vitamins

A, D, E, and KWater soluble vitamins

B and CAntioxidant vitamins

End