Gastrointestinal Gastrointestinal PhysiologyPhysiology

(Digestive System)(Digestive System)Dr. G. AHMADDr. G. AHMAD

Assistant Professor PhysiologyAssistant Professor Physiology

Functions of the Digestive Functions of the Digestive SystemSystem

Ingest foodIngest food

Break down food into nutrient moleculesBreak down food into nutrient molecules

Absorb molecules into the bloodstreamAbsorb molecules into the bloodstream

Rid the body of indigestible remainsRid the body of indigestible remains

Main Divisions of the Digestive Main Divisions of the Digestive SystemSystem

Alimentary CanalAlimentary Canal Continuous, muscular digestive tube winding Continuous, muscular digestive tube winding

throughout the bodythroughout the body Digests and absorbs food particlesDigests and absorbs food particles Contains the following organs:Contains the following organs:

Mouth, Pharynx, Esophagus, Stomach, Small and Mouth, Pharynx, Esophagus, Stomach, Small and Large IntestinesLarge Intestines

Accessory Digestive OrgansAccessory Digestive Organs Contains the following organs:Contains the following organs:

Teeth, Tongue, Gallbladder, Salivary Glands, Liver, Teeth, Tongue, Gallbladder, Salivary Glands, Liver, and Pancreasand Pancreas

Digestive System DivisionsDigestive System Divisions

Digestive ProcessesDigestive Processes IngestionIngestion Mechanical Mechanical

digestiondigestion PropulsionPropulsion Chemical digestionChemical digestion AbsorptionAbsorption DefecationDefecation

Actions of Digestive (GI) Actions of Digestive (GI) TractTract

IngestionIngestion Occurs when material Occurs when material

enters via the mouthenters via the mouth Mechanical ProcessingMechanical Processing

Crushing / Shearing – Crushing / Shearing – makes material easier makes material easier to move through the to move through the tracttract

DigestionDigestion Chemical breakdown of Chemical breakdown of

food into small organic food into small organic compounds for compounds for absorptionabsorption

SecretionSecretion Release of water acids, Release of water acids,

buffers, enzymes & salts buffers, enzymes & salts by epithelium of GI tract by epithelium of GI tract and glandular organsand glandular organs

AbsorptionAbsorption Movement of organic Movement of organic

substrates, electrolytes, substrates, electrolytes, vitamins & water across vitamins & water across digestive epitheliumdigestive epithelium

ExcretionExcretion Removal of waste Removal of waste

products from body products from body fluidsfluids

Features and Functions of the Features and Functions of the MouthMouth

Buccal/oral cavityBuccal/oral cavity Contains stratified squamous epitheliumContains stratified squamous epithelium Vestibule: Vestibule: area bounded by lips and area bounded by lips and

cheeks externally and teeth and gums cheeks externally and teeth and gums internallyinternally

Lips: Lips: posses no sweat or oil glandsposses no sweat or oil glands Palate: Palate: forms roof of the mouth, soft forms roof of the mouth, soft

and hard palate, uvulaand hard palate, uvula

Features and Functions of the Features and Functions of the TongueTongue

Helps grind food into a Helps grind food into a bolus bolus which which contains partially digested food and salivacontains partially digested food and saliva

Helps form words and is a sensory organ Helps form words and is a sensory organ for tastefor taste

Three surface features:Three surface features: Filiform papillae (roughness and grip)Filiform papillae (roughness and grip) Fungiform papillae (contains taste buds)Fungiform papillae (contains taste buds) Foliate papilae (contains taste buds)Foliate papilae (contains taste buds) Circumvallate papillae (contains taste buds)Circumvallate papillae (contains taste buds)

Papillae of the TonguePapillae of the Tongue

Features and Functions of the Features and Functions of the Salivary GlandsSalivary Glands

Main functions:Main functions: Produces and secretes salivaProduces and secretes saliva Cleanses the mouthCleanses the mouth Dissolves food chemicals so they can be Dissolves food chemicals so they can be

tastedtasted Moistens food, compacting it into a bolusMoistens food, compacting it into a bolus Begins the chemical breakdown of foodBegins the chemical breakdown of food

Salivary amylase: starchSalivary amylase: starch

Types of Salivary GlandsTypes of Salivary Glands Submandibular GlandsSubmandibular Glands

Found underneath the mandibleFound underneath the mandible Sublingual GlandsSublingual Glands

Found underneath the tongueFound underneath the tongue Parotid GlandsParotid Glands

Found anterior to the ear between masseter and Found anterior to the ear between masseter and skinskin

Saliva travels to oral orifice via ducts from Saliva travels to oral orifice via ducts from all three glandsall three glands

Anatomy of the Salivary Anatomy of the Salivary GlandsGlands

Composition of Saliva: 97-99.5% Composition of Saliva: 97-99.5% waterwater

0.5 % electrolytes0.5 % electrolytes Sodium, potassium, chloride, Sodium, potassium, chloride,

phosphate, and bicarbonatephosphate, and bicarbonate Most important proteins are salivary Most important proteins are salivary

amylase, mucus and lysozymesamylase, mucus and lysozymes

Features and Functions of the Features and Functions of the TeethTeeth

Break food into smaller parts, Break food into smaller parts, increasing surface area for digestionincreasing surface area for digestion

Types of TeethTypes of Teeth Deciduous Teeth (“baby” teeth)Deciduous Teeth (“baby” teeth) Permanent TeethPermanent Teeth

Incisors- cutting and shreddingIncisors- cutting and shredding Canines- piercing and tearingCanines- piercing and tearing Molars- grindingMolars- grinding Premolars- grinding and crushingPremolars- grinding and crushing

Tooth StructureTooth Structure CrownCrown: exposed : exposed

portion of tooth portion of tooth covered by enamel covered by enamel which covers dentinwhich covers dentin

RootRoot: internal portion : internal portion that is beneath the that is beneath the gums (gingiva) and is gums (gingiva) and is anchored by anchored by periodontal ligamentsperiodontal ligaments

PharynxPharynx Responsible for swallowingResponsible for swallowing Swallowing is divided into oropharyngeal stage Swallowing is divided into oropharyngeal stage

and esophageal stageand esophageal stage

Features and Functions of the Features and Functions of the EsophagusEsophagus

Muscular tube that propels food to Muscular tube that propels food to stomach; bolus enters stomach through stomach; bolus enters stomach through esophageal hiatusesophageal hiatus

Esophageal glands – produce mucus to Esophageal glands – produce mucus to lubricate boluslubricate bolus

Esophageal sphincter – prevents backflow Esophageal sphincter – prevents backflow into oral cavityinto oral cavity

Cardiac sphincter- prevents backflow into Cardiac sphincter- prevents backflow into esophagus esophagus

Features and Functions of Features and Functions of the Esophagusthe Esophagus

A hollow muscular tubeA hollow muscular tube About 25 cm (10 in.) long and 2 cm About 25 cm (10 in.) long and 2 cm

(0.80 in.) wide(0.80 in.) wide Conveys solid food and liquids to Conveys solid food and liquids to

the stomachthe stomach Begins posterior to cricoid cartilage Begins posterior to cricoid cartilage Esophageal glands – produce Esophageal glands – produce

mucus to lubricate bolusmucus to lubricate bolus Esophageal sphincter – prevents Esophageal sphincter – prevents

backflow into oral cavitybackflow into oral cavity

Anatomy of the EsophagusAnatomy of the Esophagus

Digestive Processes in the Digestive Processes in the Mouth, Pharynx, and Mouth, Pharynx, and

EsophagusEsophagus Mouth processes:Mouth processes:

IngestionIngestion Mechanical digestion (e.g. salivary amylase)Mechanical digestion (e.g. salivary amylase) Initiation of PropulsionInitiation of Propulsion Mastication: chewingMastication: chewing

Pharyngeal processes:Pharyngeal processes: Deglutition = swallowingDeglutition = swallowing

Esophageal processes:Esophageal processes: Peristalsis (rhythmic contractions, involuntary)Peristalsis (rhythmic contractions, involuntary)

PeristalsisPeristalsis

Features and Functions of the Features and Functions of the StomachStomach

Temporary storage area for food and Temporary storage area for food and allows it to mix with gastric juice to allows it to mix with gastric juice to produce produce chymechyme

Regions: cardiac, fundus, body, and pyloricRegions: cardiac, fundus, body, and pyloric

Stomach FunctionStomach Function Major Functions of the StomachMajor Functions of the Stomach

Storage of ingested foodStorage of ingested food Mechanical breakdown of ingested foodMechanical breakdown of ingested food Disruption of chemical bonds in food material by Disruption of chemical bonds in food material by

acid and enzymesacid and enzymes Production of Production of intrinsic factorintrinsic factor, a glycoprotein , a glycoprotein

required for absorption of vitamin Brequired for absorption of vitamin B1212 in small in small intestineintestine

Anatomy of the StomachAnatomy of the Stomach

Gastric Juices (hormones)Gastric Juices (hormones) Simple columnar epithelium – contains Simple columnar epithelium – contains gastric gastric

pits pits that secrete that secrete gastric juicesgastric juices Goblet cells Goblet cells – secrete mucus that coats – secrete mucus that coats

stomach and prevents it from being digested stomach and prevents it from being digested itselfitself

Parietal cells Parietal cells – secrete – secrete hydrochloric acidhydrochloric acid (converts pepsinogen into pepsin) and (converts pepsinogen into pepsin) and intrinsic intrinsic factor factor (necessary for absorption of vitamin B(necessary for absorption of vitamin B12)12)

Chief cells Chief cells – secrete pepsinogen which is – secrete pepsinogen which is converted to pepsin to aid in protein digestionconverted to pepsin to aid in protein digestion

Enteroendocrine cells Enteroendocrine cells – release hormones – release hormones such as:such as: Histamine, Serotonin, Gastrin, Endorphins, and Histamine, Serotonin, Gastrin, Endorphins, and

SomatostatinSomatostatin

HistamineHistamine- activates parietal cells to release HCl- activates parietal cells to release HCl

SerotoninSerotonin- contraction of stomach muscle- contraction of stomach muscle

GastrinGastrin- gastric glands to increase secretion- gastric glands to increase secretion

EndorphinsEndorphins- natural opiates- natural opiates

SomatostatinSomatostatin- inhibits gastric secretion- inhibits gastric secretion- inhibits gastric emptying- inhibits gastric emptying

Digestive Processes in the Digestive Processes in the StomachStomach Three PhasesThree Phases

Cephalic PhaseCephalic Phase Stimulated by the thought, sight, taste, or aroma Stimulated by the thought, sight, taste, or aroma

or foodor food Inputs from olfactory receptors and taste buds Inputs from olfactory receptors and taste buds

travel to parasympathetic enteric ganglia which travel to parasympathetic enteric ganglia which then stimulate stomach glandsthen stimulate stomach glands

Gastric PhaseGastric Phase Stomach distension activates stretch receptorsStomach distension activates stretch receptors Food chemicals (e.g. peptides, rising pH) activate Food chemicals (e.g. peptides, rising pH) activate

chemoreceptors which activate G cells which chemoreceptors which activate G cells which secrete gastrinsecrete gastrin

Intestinal PhaseIntestinal Phase Presence of low pH and partially digested foods in Presence of low pH and partially digested foods in

duodenum stimulates intestinal gastrin secretionduodenum stimulates intestinal gastrin secretion

Digestive Processes in the Digestive Processes in the StomachStomach

Gastric Motility and Gastric Motility and EmptyingEmptying

Peristaltic waves approach stomach and become Peristaltic waves approach stomach and become stronger near pyloric regionstronger near pyloric region

Pyloric sphincter allows ~ 3 mL of chyme to pass Pyloric sphincter allows ~ 3 mL of chyme to pass to duodenum and the rest to return to stomach to duodenum and the rest to return to stomach for further mixingfor further mixing

Small IntestineSmall Intestine 90% of absorption occurs in the small 90% of absorption occurs in the small

intestineintestine

Small IntestineSmall Intestine The Duodenum The Duodenum

The segment of small intestine closest to stomachThe segment of small intestine closest to stomach 25 cm (10 in.) long25 cm (10 in.) long ““Mixing bowlMixing bowl”” that receives that receives chymechyme from stomach from stomach

and digestive secretions from pancreas and liverand digestive secretions from pancreas and liver Functions of the duodenum Functions of the duodenum

To receive chyme from stomachTo receive chyme from stomach To neutralize acids before they can damage the absorptive To neutralize acids before they can damage the absorptive

surfaces of the small intestinesurfaces of the small intestine

Small IntestineSmall Intestine The Jejunum The Jejunum

Is the middle segment of small intestineIs the middle segment of small intestine 2.5 meters (8.2 ft) long2.5 meters (8.2 ft) long Is the location of mostIs the location of most

Chemical digestionChemical digestion Nutrient absorptionNutrient absorption

Small villiSmall villi

Small IntestineSmall Intestine The IleumThe Ileum

The final segment of small intestineThe final segment of small intestine 3.5 meters (11.48 ft) long 3.5 meters (11.48 ft) long Ends at the Ends at the ileocecal valveileocecal valve, a sphincter , a sphincter

that controls flow of material from the that controls flow of material from the ileum into the large intestineileum into the large intestine

Small IntestineSmall Intestine Intestinal SecretionsIntestinal Secretions

Watery intestinal juiceWatery intestinal juice 1.8 liters per day enter 1.8 liters per day enter

intestinal lumenintestinal lumen Moisten chymeMoisten chyme Assist in buffering acidsAssist in buffering acids Keep digestive enzymes Keep digestive enzymes

and products of and products of digestion in solutiondigestion in solution

Intestinal MovementsIntestinal Movements Chyme arrives in Chyme arrives in

duodenumduodenum Weak peristaltic Weak peristaltic

contractions move it contractions move it slowly toward jejunumslowly toward jejunum

Microscopic Anatomy of Small Microscopic Anatomy of Small IntestineIntestine

VilliVilli: fingerlike projections that increase : fingerlike projections that increase the surface area of the SIthe surface area of the SI

MicrovilliMicrovilli: tiny projections on the plasma : tiny projections on the plasma membranes of columnar cells that appear membranes of columnar cells that appear fuzzy (i.e. brush border cells)fuzzy (i.e. brush border cells)

Crypts of LieberkuhnCrypts of Lieberkuhn: secrete intestinal : secrete intestinal juice and special lysozymes that protect juice and special lysozymes that protect against bacteriaagainst bacteria

Peyer’s PatchesPeyer’s Patches: aggregated lymphoid : aggregated lymphoid tissues containing lymphocytes tissues containing lymphocytes

Microscopic Anatomy of the Microscopic Anatomy of the Small IntestineSmall Intestine

Secretions of the Small Secretions of the Small IntestineIntestine

SecretinSecretin: released by enteroendocrine cells : released by enteroendocrine cells when acidic chyme enters SI; causes release of when acidic chyme enters SI; causes release of bicarbonate-rich pancreatic juicesbicarbonate-rich pancreatic juices

SomatostatinSomatostatin: slows gastric motility and : slows gastric motility and emptying and inhibits production of gastric emptying and inhibits production of gastric secretionssecretions

Cholecystokinin (CCK)Cholecystokinin (CCK): released when fatty, : released when fatty, protein-rich chyme enters SI; causes release of protein-rich chyme enters SI; causes release of enzyme-rich pancreatic juices and bileenzyme-rich pancreatic juices and bile

Brush border enzymesBrush border enzymes: process long peptides, : process long peptides, nucleic acids, and sugars into smaller onesnucleic acids, and sugars into smaller ones

After Digestion: After Digestion: AbsorptionAbsorption

Protein Fats

Functions of the LiverFunctions of the Liver Largest internal organLargest internal organ Functions: Functions:

Filters and processes nutrient-rich blood Filters and processes nutrient-rich blood of carbohydrates, proteins, and lipids of carbohydrates, proteins, and lipids from intestinefrom intestine

Production and regulation of cholesterolProduction and regulation of cholesterol Production of Production of bile bile which emulsifies fatswhich emulsifies fats Removes drugs and hormones from Removes drugs and hormones from

circulationcirculation Storage of vitamins and mineralsStorage of vitamins and minerals

Anatomy of the LiverAnatomy of the Liver Right and Left LobesRight and Left Lobes: separated by : separated by

falciform ligamentfalciform ligament Caudate and Quadrate LobesCaudate and Quadrate Lobes: found on : found on

posterior sideposterior side Blood vessels:Blood vessels:

Hepatic artery/vein and hepatic portal Hepatic artery/vein and hepatic portal veinvein

GallbladderGallbladder: found underneath left lobe, : found underneath left lobe, stores bilestores bile

Gross Anatomy of the LiverGross Anatomy of the Liver

Microscopic Anatomy of the Microscopic Anatomy of the LiverLiver

Liver LobulesLiver Lobules: structural unit of liver: structural unit of liver HepatocytesHepatocytes: liver cells contained within the lobules: liver cells contained within the lobules Hepatic portal vein & Hepatic ArteryHepatic portal vein & Hepatic Artery: the : the

circulation of the liver, they bring blood into the liver circulation of the liver, they bring blood into the liver where it is filtered through the where it is filtered through the liver sinusoidal liver sinusoidal capillariescapillaries

Kupffer cellsKupffer cells: remove debris: remove debris Filtered blood drains into the central vein, then to the Filtered blood drains into the central vein, then to the

hepatic vein, and eventually to the inferior vena cavahepatic vein, and eventually to the inferior vena cava BileBile (produced by hepatocytes) drains into the (produced by hepatocytes) drains into the bile bile

ductduct after passing through after passing through portal triadportal triad Bile then shipped to gallbladder for storageBile then shipped to gallbladder for storage

Microscopic Anatomy of the Microscopic Anatomy of the LiverLiver

Function and Regulation of Function and Regulation of BileBile

Bile ducts are present at every portal triadBile ducts are present at every portal triad Bile flows down Bile flows down bile canaliculi bile canaliculi (tiny canals) (tiny canals)

between adjacent hepatocytes towards bile between adjacent hepatocytes towards bile duct branches at every portal triadduct branches at every portal triad

Bile enters the bile ducts which drain into Bile enters the bile ducts which drain into the the common hepatic ductcommon hepatic duct

Bile Bile emulsifies emulsifies fats, separating them into fats, separating them into smaller partssmaller parts

BilirubinBilirubin: the chief bile pigment, a waste : the chief bile pigment, a waste product of the heme of hemoglobin formed product of the heme of hemoglobin formed during the breakdown of worn-out during the breakdown of worn-out erythrocyteserythrocytes

Regulation of Bile Regulation of Bile ProductionProduction

Bile exits Bile exits cystic ductcystic duct upon stimulationupon stimulation

CCK released when CCK released when acidic, fatty chyme acidic, fatty chyme enters intestinesenters intestines

Causes:Causes: Gallbladder ContractionGallbladder Contraction Pancreatic Juice SecretionPancreatic Juice Secretion Relaxation of Relaxation of

hepatopancreatic hepatopancreatic sphinctersphincter

Features and Functions of the Features and Functions of the PancreasPancreas

Pancreatic Juice secreted by Pancreatic Juice secreted by acinar acinar cellscells Islets of Langerhans Islets of Langerhans release release insulin insulin and and

glucagon glucagon (important in glucose metabolism)(important in glucose metabolism) Pancreatic Juice contains:Pancreatic Juice contains:

Sodium Bicarbonate (buffers HCl in stomach)Sodium Bicarbonate (buffers HCl in stomach) Proteases (break down polypeptides)Proteases (break down polypeptides) Pancreatic amylase (digests oligosaccarides and Pancreatic amylase (digests oligosaccarides and

disaccharides into monosaccharides)disaccharides into monosaccharides) Pancreatic lipases (break down lipids into fatty Pancreatic lipases (break down lipids into fatty

acids and glycerol)acids and glycerol) Pancreatic nucleases (break down nucleic acids)Pancreatic nucleases (break down nucleic acids)

Anatomy of the PancreasAnatomy of the Pancreas

Features and Functions of the Features and Functions of the Large IntestineLarge Intestine

Functions:Functions: Reabsorption of remaining water and Reabsorption of remaining water and

electrolyteselectrolytes Production and absorption of Vitamins B Production and absorption of Vitamins B

and Kand K Elimination of fecesElimination of feces

Diameter is only 7 cm but is larger Diameter is only 7 cm but is larger than that of the small intestinethan that of the small intestine

Gross Anatomy of the Large Gross Anatomy of the Large IntestineIntestine

Teniae ColiTeniae Coli: bands of smooth muscle that create : bands of smooth muscle that create pocket-like sacs (pocket-like sacs (haustra)haustra)

CecumCecum: sac-like connection between the small : sac-like connection between the small and large intestinesand large intestines

AppendixAppendix: small structure containing lymphoid : small structure containing lymphoid tissue; small immune functiontissue; small immune function

Ascending, Descending, Transverse, and Ascending, Descending, Transverse, and Sigmoid ColonSigmoid Colon

Splenic and hepatic flexureSplenic and hepatic flexure RectumRectum: storage area: storage area AnusAnus: regulates defecation with two sphincter : regulates defecation with two sphincter

muscles; internal and external muscles; internal and external

Anatomy of the ColonAnatomy of the Colon

Microscopic Anatomy of the Microscopic Anatomy of the Large IntestineLarge Intestine

Simple columnar epithelium for absorption Simple columnar epithelium for absorption except in the anal canal where there is except in the anal canal where there is stratified squamousstratified squamous

No villi, no digestive-secreting cellsNo villi, no digestive-secreting cells Goblet cells produce mucus for lubrication Goblet cells produce mucus for lubrication

of of fecesfeces Bacterial flora synthesize vitamin B and Bacterial flora synthesize vitamin B and

most of the vitamin K needed for blood most of the vitamin K needed for blood clottingclotting

The Process of Absorption The Process of Absorption

Clinical CornerClinical Corner GastritisGastritis- Inflammation of gastric mucosa- Inflammation of gastric mucosa

Caused by chronic bacterial infectionCaused by chronic bacterial infection Ingestion of irritating substances e.g. Ingestion of irritating substances e.g.

alcohol/asprine alcohol/asprine AchlorhydriaAchlorhydria :absence of HCL secretion :absence of HCL secretion HypochlorhydriaHypochlorhydria: diminished acid secretions: diminished acid secretions Pernicious AnemiaPernicious Anemia: occurs when intrinsic factor is not secreted. : occurs when intrinsic factor is not secreted.

Absorption of Vit B12 does not occur leading to Pernicious anemia Absorption of Vit B12 does not occur leading to Pernicious anemia (large immature red blood ells)(large immature red blood ells)

Clinical CornerClinical Corner Peptic Ulcer: Peptic Ulcer: The damaged are of stomach or The damaged are of stomach or

upper part of small intestine mucosa caused by upper part of small intestine mucosa caused by the digestive action of gastric or small intestinal the digestive action of gastric or small intestinal secretions. secretions.

Causes: Causes: i) imbalance between gastric and intestinal i) imbalance between gastric and intestinal

secretion and the protective coating of mucosasecretion and the protective coating of mucosa ii)Helicobacter bacterial infectionii)Helicobacter bacterial infection iii) smoking, alcohol and aspirineiii) smoking, alcohol and aspirine

Clinical CornerClinical Corner SprueSprue: Decreased or malabsorption of : Decreased or malabsorption of

nutrientsnutrients CirrohsisCirrohsis - scarred liver due to chronic - scarred liver due to chronic

inflammationinflammation Hepatitis - A,B,C,D, and E Hepatitis - A,B,C,D, and E Biliary calculi Biliary calculi - gall stones - crystals of - gall stones - crystals of

cholesterol in bilecholesterol in bile Borborygmus Borborygmus - rumbling noise caused by - rumbling noise caused by

gas through intestines gas through intestines

Cholecystitis - inflammation of gall Cholecystitis - inflammation of gall bladder bladder

Colitis - inflammation of colon Colitis - inflammation of colon Dysphagia - difficulty in swallowingDysphagia - difficulty in swallowing Enteritis - inflammation of the intestines Enteritis - inflammation of the intestines ConstipationConstipation Diarrhea Diarrhea

Clinical corner