19 Unit 1 Chapter 19. 19 Unit 1 Tube that includes: mouth, Pharynx, Esophagus, Stomach, Small...
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Transcript of 19 Unit 1 Chapter 19. 19 Unit 1 Tube that includes: mouth, Pharynx, Esophagus, Stomach, Small...
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The Digestive SystemThe Digestive SystemThe Digestive SystemThe Digestive System
Chapter 19
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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
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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
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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 19.2Figure 19.2
Figure 19.3aFigure 19.3a
Figure 19.3bFigure 19.3b
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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
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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
Figure 19.4Figure 19.4
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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
Figure 19.5Figure 19.5
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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
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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
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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
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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
Figure 19.7Figure 19.7
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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
Figure 19.8Figure 19.8
Figure 19.9Figure 19.9
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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
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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
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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
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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
Figure 19.10Figure 19.10
Figure 19.11aFigure 19.11a
Figure 19.11bFigure 19.11b
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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
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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
Figure 19.12aFigure 19.12a
Figure 19.12bFigure 19.12b
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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
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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
Figure 19.13Figure 19.13
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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
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Digestion & AbsorptionDigestion & AbsorptionDigestion & AbsorptionDigestion & Absorption
• 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
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Carbohydrate DigestionCarbohydrate DigestionCarbohydrate DigestionCarbohydrate Digestion
• Amylases: Starch & dextrin maltose
• Disaccharidases at surface:Maltose: maltose glucoseSucrase: sucrose glucose &
fructoseLactase: lactose glucose &
galactose
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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
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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
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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
Figure 19.14aFigure 19.14a
Figure 19.14bFigure 19.14b
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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
Figure 19.15aFigure 19.15a
Figure 19.15bFigure 19.15b
Figure 19.16Figure 19.16
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Digestion & AbsorptionDigestion & AbsorptionDigestion & AbsorptionDigestion & Absorption
• 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
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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
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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)
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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
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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