digestive system
DESCRIPTION
Digestive System. Digestive system functions. Ingestion Mixing and movement of food. Peristalysis Digestion of foods. Chemical Mechanical Absorption of digested foods. Defecation. Layers of the GI tract. Alimentary canal vs Accessory organs. - PowerPoint PPT PresentationTRANSCRIPT
DigestiveDigestive
System System
Digestive system Digestive system functionsfunctions
1.1. IngestionIngestion
2.2. Mixing and Mixing and movement of movement of food.food.
– PeristalysisPeristalysis
3.3. Digestion of Digestion of foods.foods.
– ChemicalChemical– MechanicalMechanical
4.4. Absorption of Absorption of digested foods.digested foods.
5.5. Defecation.Defecation.
Layers of the GI Layers of the GI tracttract
• Alimentary canal Alimentary canal vs Accessory vs Accessory organs.organs.
• Wall of GI tract Wall of GI tract is composed of is composed of four layers four layers ((inside->outsideinside->outside))– MucosaMucosa– SubmucosaSubmucosa– MuscularisMuscularis– SerosaSerosa
• PeritoneumPeritoneum• MesenteryMesentery
Layers of the GI tract
Salivary GlandsSalivary Glands
• Saliva is secreted Saliva is secreted from 3 pairs of glandsfrom 3 pairs of glands
• Parotid glands Parotid glands (back)(back)
• Submandibular glands Submandibular glands (jaw)(jaw)
• Sublingual Sublingual (below (below tongue)tongue)
• Composition of saliva:Composition of saliva:– 99.5% water99.5% water– 0.5% solutes0.5% solutes
• Salivary amylase- Salivary amylase- (digestive enzyme for (digestive enzyme for starch)starch)
• Mucus (lubrication)Mucus (lubrication)• lysozyme (kills lysozyme (kills bacteria)bacteria)
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Control of Control of Salivary Salivary GlandsGlands
– Parasympathetic Parasympathetic ANS stimulates ANS stimulates production of production of saliva.saliva.
– Stimuli:Stimuli:• Food touching the Food touching the tonguetongue
• SmellSmell• TasteTaste• Thought of food.Thought of food.
Chewing
• Mechanical digestion involves– Muscular manipulation by the tongue
– Teeth grind food into smaller pieces
– Saliva mixes inResult: a soft, flexible, easily swallowed mass called a bolus
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• Voluntary stageVoluntary stage– Bolus is pushed Bolus is pushed to back of mouth to back of mouth by tongue.by tongue.
• Pharyngeal stagePharyngeal stage– Breathing stops.Breathing stops.– Bolus passes Bolus passes through pharynxthrough pharynx
• Esophageal stageEsophageal stage– PeristalysisPeristalysis– HeartburnHeartburn
EsophagusEsophagus
• Connects mouth to Connects mouth to stomach.stomach.
• Lies behind the Lies behind the trachea (flat trachea (flat side)side)
• Passes through Passes through the diaphragmthe diaphragm
• Contains two Contains two layers of smooth layers of smooth muscle.muscle.
• Food has to pass Food has to pass over trachea @ over trachea @ epiglottisepiglottis
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StomachStomach• J shaped, lies J shaped, lies under diaphragm.under diaphragm.
• A mixing chamber A mixing chamber and holding and holding reservoir- size reservoir- size variesvaries
• Divided into four Divided into four areas:areas:– CardiaCardia– Fundus Fundus – BodyBody– Pylorus/ Pyloric Pylorus/ Pyloric sphinctersphincter
• RugaeRugae
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Wall of Wall of StomachStomach
• 4 layers:4 layers:• MucosaMucosa• SubmucosaSubmucosa• Muscularis: 3 Muscularis: 3 layers of layers of musclemuscle– Longitudinal Longitudinal layerlayer
– Circular layerCircular layer– Oblique layerOblique layer
• SerosaSerosa
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Gastric Gland Gastric Gland secretionssecretions
• Mucous cellsMucous cells– MucusMucus
• Chief cellsChief cells– PepsinogenPepsinogen
• Parietal CellsParietal Cells– HCLHCL– Intrinsic factor Intrinsic factor (B12)(B12)
• G cellsG cells– Gastrin (hormone)Gastrin (hormone)
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Stomach & Stomach & DigestionDigestion
• Mechanical Mechanical digestiondigestion– Bolus converted to Bolus converted to chyme.chyme.
– Mixing waves push Mixing waves push chyme into duodenum.chyme into duodenum.
– Pyloric sphincter Pyloric sphincter releases into SIreleases into SI
• Chemical digestionChemical digestion– PepsinPepsin breaks down breaks down proteins into proteins into peptides.peptides.
– LipaseLipase digests digests triglycerides (in triglycerides (in acid) into acid) into diglyceridesdiglycerides
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Stomach & Stomach & AbsorptionAbsorption
• Mucus protects Mucus protects the stomach the stomach lining from being lining from being digested itselfdigested itself
• Little absorption Little absorption of nutrients hereof nutrients here
• Stomach wall Stomach wall doesdoes absorb:absorb:– WaterWater– ElectrolytesElectrolytes– Some drugs Some drugs (aspirin)(aspirin)
– AlcoholAlcohol
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PancreasPancreas• Pancreas lies Pancreas lies behind the stomachbehind the stomach
• Secretions pass Secretions pass through pancreatic through pancreatic duct into duodenumduct into duodenum
• Pancreatic juice:Pancreatic juice: BicarbonateBicarbonate counteracts acid counteracts acid from chyme from chyme
• Digestive enzymes Digestive enzymes • Islets of Islets of Langerhans Langerhans produce produce hormones: insulinhormones: insulin
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Enzymes produced by the pancreas that work in the
small intestine:1. Pancreatic amylase – turns starches to
dissacharides2. Trypsin - proteins to
polypeptides.3. Chymotrypsin - proteins to peptides.4. Carboxypeptidase - proteins to peptides.5. Pancreatic lipase - triglycerides to fatty
acids & monoglcerides6. Ribonuclease -nucleic acid digestion
LiverLiver• Heaviest gland in Heaviest gland in the body: 3 lbs.the body: 3 lbs.
• Involved in Involved in filtration,filtration,
storage (glycogen), storage (glycogen), protein protein metabolism, and metabolism, and excretionexcretion
• Produces Produces bilebile– Emulsifies lipids Emulsifies lipids (fats)(fats)
– Bile leaves liver Bile leaves liver through through cystic cystic duct.duct.
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Gall Bladder Gall Bladder • Bile (made in the Bile (made in the liver) is liver) is storedstored in in the gall bladder.the gall bladder.
• Carried by cystic Carried by cystic duct to common bile duct to common bile duct, then released duct, then released into duodenum.into duodenum.
• Bile emulsifies Bile emulsifies lipidslipids
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Gall stones (crystallized cholesterol)
Small IntestineSmall Intestine
• Composed of Composed of – DuodenumDuodenum– JejunumJejunum– IleumIleum
• Food is released Food is released through through ileocecal ileocecal sphincter into sphincter into the cecumthe cecum
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Small IntestineSmall Intestine
• MucosaMucosa• Villi extend Villi extend from wall of sm. from wall of sm. intestine.intestine.– Capillary networkCapillary network– Lacteal- lymphLacteal- lymph– Duodenal glands-Duodenal glands-secrete alkaline secrete alkaline mucusmucus
– Microvilli-Microvilli-increases surface increases surface area for area for absorptionabsorption
Enzymes produced by Enzymes produced by small intestinesmall intestine
• Maltase maltose to glucose• Sucrase sucrose to glucose & fructose
• Lactase lactose to glucose & galactose
• Peptidases peptides to amino acids
• Ribonuclease RNA to sugar & bases
• Deoxyribonuclease DNA to sugar & bases
Absorption in the Absorption in the Small IntestineSmall Intestine
• Carbohydrates & Carbohydrates & proteins move proteins move into into capillaries.capillaries.
• Fatty acids & Fatty acids & monoglycerides monoglycerides move into the move into the lacteal (lymph lacteal (lymph capillaries)capillaries)
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Large Intestine/ Large Intestine/ coloncolon
• 5 ft in length/2.5 5 ft in length/2.5 inches diameterinches diameter
• Ileocecal sphincter: Ileocecal sphincter: allows material to allows material to pass from sm. pass from sm. intestine to the intestine to the coloncolon
• Has ascending, Has ascending, transverse, transverse, descending, and descending, and sigmoid portions.sigmoid portions.
• Puckered due to Puckered due to contraction of contraction of muscular bands muscular bands (teniae coli)(teniae coli)
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Digestion Digestion and and absorptionabsorption– Bacteria Bacteria ferment ferment
& digest food- & digest food- releasing Hreleasing H22, CO, CO2, 2,
methane gases methane gases (flatulence)(flatulence)
– Bacteria produce Bacteria produce vitamin B & K vitamin B & K (absorbed by (absorbed by colon)colon)
– Bacteria break Bacteria break down bilirubin- down bilirubin- brown color brown color
– Absorbs much of Absorbs much of the the waterwater and and ions, forming ions, forming feces.feces.
AppendixAppendix• Structure:Structure:
– Short finger-like Short finger-like extension of the lg. extension of the lg. intestineintestine
– Attaches to the cecumAttaches to the cecum– Stores a sample of Stores a sample of healthy colon healthy colon bacteria, to re-bacteria, to re-colonize the colon colonize the colon after an intestinal after an intestinal disease.disease.
Appendicitis: Appendicitis: inflammation inflammation requiring removal of requiring removal of the appendixthe appendix
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Inflamed appendix
Defecation Defecation reflexreflex– Mass peristalysis Mass peristalysis pushes pushes
contents from the contents from the sigmoid colon to the sigmoid colon to the rectumrectum
– Stretch receptors Stretch receptors initiate the defecation initiate the defecation reflexreflex
– Initiated by food in Initiated by food in the stomach/ ANS the stomach/ ANS controlled.controlled.
– Internal sphincter- Internal sphincter- (involuntary) opens(involuntary) opens
– External sphincter External sphincter releases (voluntary releases (voluntary control)control)
+ downward pushing of the + downward pushing of the diaphragm diaphragm push out the push out the fecesfeces
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Colon cancer
• One of the deadliest cancers
• Detected by stool samples, or sigmoid/colonoscopies
• Polyp removal using a wire snare
Healthy colon