19 Unit 1 Chapter 19. 19 Unit 1 Tube that includes: mouth, Pharynx, Esophagus, Stomach, Small intestine, Large intestine Accessory organs: teeth, tongue,

19

Uni

t 1

The Digestive SystemThe Digestive SystemThe Digestive SystemThe Digestive System

Chapter 19

19

Uni

t 1

Gastrointestinal (GI) Gastrointestinal (GI) TractTract

Gastrointestinal (GI) Gastrointestinal (GI) TractTract

• Tube that includes: mouth, Pharynx, Esophagus, Stomach, Small intestine, Large intestine

•Accessory organs: teeth, tongue, salivary glands, liver, gallbladder, and pancreas

Figure 19.1Figure 19.1

19

Uni

t 1

Overview- OperationsOverview- OperationsOverview- OperationsOverview- Operations

• Ingestion: eating• Secretion: release of water,

enzymes & buffers• Mixing & propulsion: movement

along GI tract• Digestion: mechanical and chemical

breakdown of foods• Absorption: getting it into the body• Defecation: dumping waste

products = defecation

19

Uni

t 1

Wall Layers- EverywhereWall Layers- EverywhereWall Layers- EverywhereWall Layers- Everywhere

• 4 layers• Mucosa- epithelium, connective layer,

glands, muscularis mucosae

• Submucosa- connective tissue, blood vessels, lymphatic vessels, enteric nervous system

• Muscularis- circular layer, longitudinal layerIn mouth, pharynx & upper esophagus –skeletal

muscleAlso in external anal sphincter

• Serosa or Visceral peritoneum


Figure 19.3aFigure 19.3a

Figure 19.3bFigure 19.3b

19

Uni

t 1

MouthMouthMouthMouth

• Formed by cheeks, hard & soft palate & tongue

• Soft palate at back includes a “hangy down” part = uvulaDuring swallowing uvula prevents entry

into nasal cavity• Tongue- muscular accessory organ

maneuvers food for chewingAdjusts shape for speech & swallowing

• Lingual tonsils at base of tongue

19

Uni

t 1

Salivary GlandsSalivary GlandsSalivary GlandsSalivary Glands

• 3 pairs of salivary glandsDucts empty into oral cavity

• Parotid- inferior & anterior to ears

• Submandibular- in floor of mouth, medial & inferior to mandible

• SublingualBeneath tongue and superior to submandibular

• Saliva contains 99.5% water, salivary amylase, mucus and other solutesDissolves food & starts digestion of starches


19

Uni

t 1

TeethTeethTeethTeeth

• Accessory organs in bony sockets of mandible & maxilla

• 3 external regions: Crown- above gumsRoot- 1 or more parts embedded in socketNeck – between crown and root near gum

line• 3 layers of material

Enamel- covers crownDentin- majority of interior of toothPulp cavity - nerve, blood vessel & lymphatics


19

Uni

t 1

Digestion in the MouthDigestion in the MouthDigestion in the MouthDigestion in the Mouth

• Mechanical breakdown- chewing• Mixed with saliva by tongue• Salivary amylase chemically breaks

down polysaccharides (starch)maltose and larger fragmentsContinues in the stomach until

acidified• Rounds up food into a soft bolus

for swallowing

19

Uni

t 1

Pharynx & EsophagusPharynx & EsophagusPharynx & EsophagusPharynx & Esophagus

• On swallowing:• Bolus of food oropharynx• Laryngopharynx esophagus

Muscular contractions in pharynx help

• Upper esophageal sphincter (UES)Skeletal muscle –controls entry to esophagus

• Lower esophageal sphincter (LES)Smooth muscle- regulates entry to stomach

Figure 19.6a,bFigure 19.6a,b

19

Uni

t 1

SwallowingSwallowingSwallowingSwallowing

• Voluntary: bolus forced into oropharynx

• Triggers oropharyngeal stageInvoluntary & breathing interruptedSoft palate move up-close nasopharynxEpiglottis seals off larynxBolus moves into esophagus through UES

• Esophageal stage peristalsis moves it toward stomach

Figure 19.6cFigure 19.6c

19

Uni

t 1

StomachStomachStomachStomach

• J- shaped enlargement of tract• Serves as mixing chamber and

holding reservoir• Very elastic & muscular• 4 regions

Cardia- surrounds upper openingFundus- superior & to left of cardiaBody – large central portionPylorus- lower part leading to pyloric

sphincter & duodenum


19

Uni

t 1

Stomach WallStomach WallStomach WallStomach Wall

• Mucosa:Folds called rugaeEpithelium- simple columnar mucousForm gastric glands lining gastric pits

• Secretory cells: mucous neck cellsChief cells inactive enzyme pepsinogeParietal cells HCl & intrinsic factorColl4ectively = gastric juice

• Muscularis- 3 Layers: longitudinal, circular & oblique



19

Uni

t 1

Digestion & AbsorptionDigestion & AbsorptionDigestion & AbsorptionDigestion & Absorption

• Food entry stretch & rise in pHNerve impulses secretion & mixing

waves Food mixed with juice ChymeSmall amount pushed through pyloric sphincter= gastric emptying- Carb. foods fastest, lipids

next & proteins slowestEntry in duodenum feedback inhibition of

stomach activity

• Pepsin digests protein peptides• Little absorption- water, ions & some

drugs

19

Uni

t 1

PancreasPancreasPancreasPancreas

• Behind stomach- Produces pancreatic juice in acinar cellsto duodenum via pancreatic duct

• NaHCO3 solution (pH 7.1-8.2)– 1000ml/dayNeutralize stomach acid and dilutes chyme

• Panceas- digestive enzymesProteases: chymotrypsinogen, trypsinogen, et.

al.Activated by entreokinase from intestineStarch digesting- pancreatic amylasePancreatic lipaseNucleotidases – RNAase & DNAase

19

Uni

t 1

Liver & Gall BladderLiver & Gall BladderLiver & Gall BladderLiver & Gall Bladder

• Largest organ after the skin• On right below diaphragm• Functional unit is lobule-

Hepatocytes around central veinOpen capillaries = sinusoids

• Bile canaliculi ducts hepatic duct

Gall bladder =Pear-shaped organ on front (stores bile)

cystic duct common bile duct

19

Uni

t 1

BileBileBileBile

• Bicarbonate, bile salts & waste. – 1000 ml/day

• Important for emulsifying fats Increases surface area for digestion

• Pigment is bilirubin- from broken-down heme during RBC recycling

• Digested to strecobilin- brown color• Bile salts reabsorbed at end of small

intestine- ileum• recycle to liver in portal circulation




19

Uni

t 1

Liver FunctionLiver FunctionLiver FunctionLiver Function

• Maintains blood glucoseStores as glycogen Uses absorbed sugars & Converts amino

acids glucose• Lipid metabolism

Produces cholesterol & triglycerides, makes bile

Makes lipoproteins for lipid transport• Excretion of bilirubin• Processes drugs and other chemicals• Store fat soluble vitamins• Make active vitamin D

19

Uni

t 1

Small IntestineSmall IntestineSmall IntestineSmall Intestine

• 3 parts: duodenum, jejunum, ileum

• Where most of the digestion occurs

• Essentially all of the nutrient absorption

• Ends in ileocecal sphincter



19

Uni

t 1

Wall StructureWall StructureWall StructureWall Structure

• Same 4 layers• Epithelial- simple columnar

Absorptive cells with microvilliGoblet cells- secrete mucus

• Intestinal glands- intestinal juice & hormonesSecretin, cholecystokinin (CCK), Glucose-

dependent-insulinotrophic peptide (GIP)

• Lymphatic tissue- defense

19

Uni

t 1

Wall Structure (Cont.)Wall Structure (Cont.)Wall Structure (Cont.)Wall Structure (Cont.)

• Duodenal glands- alkaline mucusHelps neutralize stomach acid

• Circular folds- increase surface area

• Villi- finger like projections of mucosaIncrease surface area for absorptionInclude lacteals for lipid absorption


19

Uni

t 1

Motility & SecretionsMotility & SecretionsMotility & SecretionsMotility & Secretions

• Secretions: alkaline, some enzymesPeptidases-breaks small peptidesDisaccharidases attached to wallWater and salt to balance osmolality~2000 ml/day

• Segmentation activity- for mixing• Peristalsis for movement after most

absorption completed- slow waves

19

Uni

t 1


• Chyme enters with partially digested carbohydrates & proteins

• Bile + pancreatic juice + intestinal juice completes the job

• Absorption is of monosaccharides; amino acids; phosphate sugar & bases of DNA & RNA; fatty acids & monoglycerides

19

Uni

t 1

Carbohydrate DigestionCarbohydrate DigestionCarbohydrate DigestionCarbohydrate Digestion

• Amylases: Starch & dextrin maltose

• Disaccharidases at surface:Maltose: maltose glucoseSucrase: sucrose glucose &

fructoseLactase: lactose glucose &

galactose

19

Uni

t 1

Protein & Fat DigestionProtein & Fat DigestionProtein & Fat DigestionProtein & Fat Digestion

• Trypsin, chymotrypsin, elastase, carboxypeptidase & pepsinProteins small peptides

• Peptidases at surface:Peptides amino acids & di- & tri-

peptides

• Lipase: glycerides fatty acids &

monoglycerides

19

Uni

t 1

AbsorptionAbsorptionAbsorptionAbsorption

• By diffusion, facilitated diffusion, osmosis & active transport

• Carbohydrates monosaccharidesVia portal system to liver

• Proteins (jejunum & ileum) amino acidsVia portal system to liver

• Lipids reformed to triglyceridesPackaged in chlyomicrons with proteinVia lacteals lymphatics

19

Uni

t 1

Absorption (Cont.)Absorption (Cont.)Absorption (Cont.)Absorption (Cont.)

• Water & saltPrimarily osmotic movement along

with other nutrients

• Vitamins:Fat soluble absorbed with fatWater soluble with simple diffusionB12 combines with intrinsic factor &

absorbed by active transport in ileum



19

Uni

t 1

Large IntestineLarge IntestineLarge IntestineLarge Intestine

• Cecum, colon, rectum, anal canal• Ileocecal canal large intestine

Below is cecum with appendix• Colon- ascending, transverse,

descending & sigmoid rectum anal canal• Standard 4 layers with mucus

secretionFew folds , little specialization for absorption

• Muscularis: circular + bands of longitudinal muscle




19

Uni

t 1


• Slow emptying of ileum• Slow peristalsis• Mass peristalsis with food in

stomachMoves from middle of colon rectum

• Bacterial digestionProduce some B-vitamins & Vit. KProduce gases= flatusColon absorbs salt & water

19

Uni

t 1

Defecation ReflexDefecation ReflexDefecation ReflexDefecation Reflex

• Stretch of rectum wall neural reflex contraction of longitudinal muscle• Combined pressure + parasympathetic

activity relaxing of internal anal sphincter

• External anal sphincter is voluntary• Contraction of diaphragm & abdominal

wall muscles aid defecation

19

Uni

t 1

ControlControlControlControl

• Rule: activate forward and inhibit behind• three phases: Cephalic, gastric, intestinal• Cephalic- smell, sight, thought of food

Neural signals stimulates salivary glands & gastric glands

• Gastric- stretching, pH of stomachGastrin activates stomach & LES & relaxes pyloric

sphincterNeural signals + gastrin signal satiety (fullness)

19

Uni

t 1

Control (Cont.)Control (Cont.)Control (Cont.)Control (Cont.)

• Intestinal- responses to food entering duodenumneural & endocrine

• CCK stimulated by AA & fatsPancreatic enzyme releaseGall bladder contractionContraction of pyloric sphincter

• Acid stimulates secretinStimulates HCO3

- ions in pancreatic juiceInhibits gastrin action in stomach

19

Uni

t 1

AgingAgingAgingAging

• Decreased secretion, motility, strength of responses

• loss of taste, periodontal disease, hiatal hernia, gastritis & peptic ulcer disease

• Increased incidence of gall bladder problems, cirrhosis of liver, pancreatitis, constipation, hemorrhoids & diverticulitis

Documents

19 Unit 1 Chapter 19. 19 Unit 1 Tube that includes: mouth, Pharynx, Esophagus, Stomach, Small intestine, Large intestine Accessory organs: teeth, tongue,