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