Digestive System

Digestive SystemJoe Pistack MS/EDDigestive SystemFunction of Digestive System:Ingestion of foodDigestionAbsorption of end-productsElimination of wasteDigestive SystemThe digestive system consist of the following:Mouth PharynxEsophagusStomach Small intestineLarge intestineRectumAnus

Digestive SystemAccessory organs include:Salivary glandsTeethLiver GallbladderPancreasDigestion is process by which food is broken down into smaller particles suitable for digestionAbsorption is the process by which the end products of digestion move across the walls of the digestive tract into blood for distribution throughout the body

DigestionTwo types of digestion:Mechanical: is the breakdown of large food particles into smaller pieces by physical meansChemical digestion: is the chemical alteration of food by chemical substances such as digestive enzymes, acid & bileThe end products of digestion are absorbed across the lining of the digestive tract into the bloodDigested nutrients are utilized by the cells of the bodyAny food not digested is eliminated from the body as fecesElimination is the last phase of digestionLayers of the Digestive TractThe walls of the digestive tract has 4 layers:Mucosa: innermost layer of the tract composed of mucous membraneContains cells that secrete mucus, digestive enzymes and hormonesDucts of exocrine glands empty into the lumen of the digestive tractSubmucosa:Thick layer of connective tissue that lies next to the mucosaContains blood vessels, nerves, glands and lymphatic vesselsLayers of the Digestive TractMuscle layerThird layer of the GI tractTwo layers of smooth muscle consisting of: inner circular layer and outer longitudinal layerAutonomic nerve fibers innervate the muscle layerResponsible for mixing movements, contraction and relaxation of the stomach muscles to aid in the mechanical digestion of foodPeristalsis also occurs in the muscle layer which is the rhythmic alternating contraction and relaxation of the muscles that push the food in forward direction through the digestive tract; stimulated by the presence of foodMuscles are also responsible for swallowing and defecation

Without peristalsis paralytic ileus; life threatning8Layers of the Digestive TractSerosa:Outermost lining of the digestive tract Extends as the peritoneal membranePeritoneal Membranes:Extension of the serosaMesentery and Mesocolon are located behind the digestive organsGreater and Lesser Omentum are located in front of organsForm flat and folded structures that:Help anchor digestive organsCarry blood and lymph vessels as well nerves to abdominal organsRestrict the spread of infection in abdominal cavity

Greater omentum is double layer of peritoneum that contains a considerable amount of fat & resembles an apron draped over abdominal organs9

Mouth Mouth Beginning of digestive tractAKA oral cavity, buccal cavityContains accessory structures:Teethtonguesalivary glandsTeeth Used to chew food and begin mechanical digestionProcess of chewing food breaking larger particles into smaller is called masticationTwo set of teeth in lifetime: Deciduous teeth: 20 teeth that appear around 6 months; baby teethPermanent teeth: 32 teeth that replace deciduous at 6-12 yearsTeeth Names teeth:IncisorsCuspids (canines)Premolars (bicuspids)Molars (include wisdom teeth)Anatomy of the toothCrown: above level of the gum (gingiva) covered with hard enamelNeck: connects crown with rootRoot : embedded in jaw boneOuter surface of root is anchored to periodontal membrane by cementum which hold tooth in placeMost of the tooth contains a bone-like material called dentinPulp is connective tissue of tooth that contains nerves and blood vessel within the pulp cavity - extends to root through the root canalTongue Is muscular organ that occupies the floor of the mouthTwo roles:Facilitates chewing and swallowing by continuously repositioning food in the mouth and assist with swallowingTo taste foodTwo structures:Mucous membrane called frenulum which anchors the tongue to the floor of the mouthCapillary network that provides sublingual area with rich blood supplyBall like mass of food is called bolussome meds given sublingually

13Salivary GlandsSalivary Glands: there are 3 pairs that secrete their contents into the mouthParotid glands: largest; lies below and anterior to the earsSubmandibular glands: located in floor of mouthSublingual glands: located under the tongue and are the smallestSecretion of the salivary glands reach mouth by way of tiny ductsSecrete saliva which is a watery fluid that contains mucus and salivary amylase (ptyalin) a digestive enzyme1 liter is secreted dailyFunction is to moisten food for swallowing

Sialolithiasis: is obstruction of the salivary gland by a stone14Hard & Soft PalateHard and soft palate form the roof of the mouthThe anterior hard palate separates the oral cavity from the nasal passagesPosterior soft palate separates the oral cavity from the nasopharynxSoft palate extends toward the back of the oral cavity as the uvulaUvula is a V-shaped piece of soft tissue that hangs down from the upper back region of the mouth and aids in swallowingThe palatine tonsils are masses of lymphoid tissue located on the sides of the posterior oral cavity and has the role of protection against infection

Pharynx Pharynx:AKA throatInvolved in swallowing by reflex action called deglutitionThree parts: Nasopharynxoropharynxlaryngopharynx Only the oropharynx & laryngopharynx are parts of digestive systemThe act of swallowing directs food from the pharynx to the esophagusThe epiglottis cover the trachea to prevent aspiration and the opening of the nasophaynx is closed during swallowing

Esophagus Esophagus:Tube-like structure that carries the food from the pharynx to the stomachApproximately 10 inches in length and descends through chest cavity penetrating the diaphragmSwallowing pushes a bolus of food into the esophagus which stimulates peristaltic activity causing the food to move into the stomachGlands in the mucosa of the esophagus secrete mucus which lubricates food to facilitate passageEsophagus Two sphincters:Pharyngoesophageal sphincter: located at the top of the esophagusGastroesophageal or lower esophageal sphincter (LES): located at the base of the esophagusSwallowing pushes food past the pharyngoesophageal sphincterRelaxation of the LES keeps the base of the esophagus open allowing passage of food into the stomachWhen contracted LES closes the base of the esophagus preventing reflux or regurgitation

Regurg causes heartburn or pyrosis due to high acidity of stomach contents20StomachStomach:Pouch-like organ that lies in the upper left quadrant of the abdominal cavity under the diaphragmPerforms 5 functions:Digestion of foodSecretion of gastric juices, digestive enzymes and hydrochloric acidSecretion of gastric hormones and intrinsic factor (a protein that helps the intestines absorb vitamin B12)Regulation of the rate and delivery of partially digested food to small intestineAbsorption of small quantities of water and dissolved substances

Stomach Regions of the stomach:Fundus - upper portion, closest to the esophagus and lower esophageal sphincterBody - middle portion of stomachPylorus - lower portion of stomach, closest to duodenumPyloric canal- continuation of the pylorusPyloric sphincter - located at the end of the pyloric canal, regulates the rate of delivery of stomach contents to small intestineLandmarks of Stomach:Greater curvatureLesser curvature

Stomach Stomach contains rugae which allows for expansion when the stomach is fullWhen empty the stomach is the size and shape of a sausageHas the capacity to expand 1 literThree layers of stomach muscle:Longitudinal muscle layerCircular muscle layerOblique muscle layerThe arrangement of the muscle layer allow for churning and mixing of food with gastric juice to create thick paste-like mixture called chymePeristalisis moves the propels the food toward the pylorus

23StomachNerves of the stomach:The stomach is innervated by the vagus nerveStimulation increases motility and secretion of gastric juicesGlands of the stomach:The mucus membranes contain gastric glandsThe glands are composed of three types of secreting cells:Mucus cells secrete mucusChief cells secrete digestive enzymesParietal cells secrete hydrochloric acid and intrinsic factorSecretion of the gastric glands are called gastric juiceThe secretion of thick mucus coats the stomach lining forming a protective barrier preventing the gastric juices from digesting the stomach itself

Small IntestineSmall intestine:Called small because the diameter is smallConsiderable length at 20 feet longLocated in the center lower abdominal cavityHeld in place by the mesentery (extension of peritoneum)Primary role is chemical digestion and absorption of foodThree parts:DuodenumJejunumileumSmall IntestineDuodenum: First segment10 inches in lengthReceives chyme from stomach and secretions from accessory organs (liver, gallbladder and pancreas)Secretions from mouth, stomach and accessory organs are responsible for digestion of all foodMost digestion and absorption occurs in the duodenumSmall IntestineJejunum:Second segment 8 feet in lengthSome digestion and absorption occurs is first portion of jejunumIleum:Third segment12 feet in length Extends from jejunum to ileocecal valveIleocecal valve prevents reflux of contents from the cecum (first part of large intestine) back into the ileumIleum is lined with lymphoid tissue called Peyers patches which diminishes the bacterial content in the digestive systemFunction of the Small IntestineThe walls of the intestine contain circular folds with fingerlike projections called villiThe epithelial cells of each villus form extensions called microvilliThe large number of villi and microvilli increase the amount of digested food that can be absorbedEach villus consists of a layer of epithelial tissue that surrounds a network of blood capillaries and a lymphatic capillaries called a lactealThe villus absorb the end products of digestion into either the blood capillaries or the lactealFunction of the Small IntestineThe capillary blood within the villus drains into the hepatic portal vein and into the liverThe end products of carbohydrates and protein digestion first go to the liver for processing before being distributed throughout bodyEnd products of fat digestion enter the lacteal, forming a milky white lymph called chyle which empties directly into the lymph systemThe walls of the small intestine also secrete several digestive enzymes and two hormones - secretin and cholecystokinin

Large IntestineLarge intestineLarger in diameter5 feet in lengthExtends from the ileocecal valve to the anus4 parts:Cecum ColonRectumAnal canalLarge IntestineCecum:First part of the large intestineLocated in the right lower quadrantAscends on the right side as the ascending colonAttached to the cecum is the appendix (a structure that contains lymphocytes and is a source of immune cellsAppendix can become inflamed and require surgical removalLarge IntestineAscending Colon:Ascends on the right side of and curves near liverTransverse Colon:Crosses the upper abdomenDescending Colon:Descends down the left side of the abdomen Sigmoid Colon:S-shaped segmentDistal end of large intestine includesRectumanal canalanus Anus contains two sphincters : internal & externalFeces is waste composed of primarily nondigestible food residue; Expulsion of feces is called defecation34

Function of Large Intestine4 Functions:Absorption of water and certain electrolytesSynthesis of certain vitamins by intestinal bacteria (K and some B vitamins)Temporary storage of fecesElimination of waste from bodyPeristaltic waves move the fecal material from the cecum into the ascending , transverse and descending colonDuring the process water is being reabsorbed from the feces, across the intestinal wall into the capillaries which makes feces a semisolid mass

If feces remains in the intestine for a extended period of time it becomes hard: constipationIf feces is expelled too fast through interstine it is loose, watery: diarrheaDrugs can affect the motility of the large intestine therefore the consistency of the feces36Fuction of the Large IntestineBacterial Action:Escherichia coli (E coli) - part of the normal flora of intestinal bacteriaE coli that is normal in intestinal tract causes serious health risks if in urine or bloodIntestinal bacteria account for 30% of fecal content and almost 100% of the aroma.

Accessory Digestive OrgansThree important organs:LiverGallbladderPancreas LiverLarge reddish-brown organ located in the RUQ in abdomen below the diaphragm and protected by rib cageLargest gland in the body2 lobes - right is larger and left lobe smaller Separated by a ligament The ligament secures the liver to the anterior abdominal wall and undersurface of the diaphragmLiver is surrounded by a tough fibrous membrane called a capsuleLiver Function Synthesis of bile salts and secretion of bile - bile salts aid in fat digestion and absorption of fat-soluble vitaminsBile secretion is the main digestive function of the liverSynthesis of plasma proteins - play role in blood volume and blood coagulationStorage of glycogen, fat-soluble vitamins (A,D,E,K) and B12 Detoxification of drugs and other harmful substances which allows for kidneys to excrete

Liver Function- continuedExcretion of bilirubin, cholestrol, drugs and other substancesMetabolism of carbohydrates which in turn regulates blood glucose levelsThe liver either stores glucose as glycogen or makes glucose from glycogen dependent upon blood glucose levelsif blood glucose is elevated it stores excess glucose as glycogenif blood glucose is low the liver converts glycogen to glucose and releases it to blood

Ammonia is toxic to humans41Liver - continuedMetabolism of protein - liver can make different amino acids Converts nitrogen (from ammonia) into urea for excretion by the kidneysMetabolism of fats - liver breaks down fatty acids, synthesizes cholestrol and phospholipids, and converts excess protein and carbohydrates into fatPhagocytosis - the kupffer cells (hepatic macrophages) can phagocytose bacteria and other substances within the liver

Blood supply to the LiverHepatic portal system:Is the livers unique arrangement of blood vessels Receives 1.5 liters of blood/minute from the portal vein and hepatic arteryThe portal vein drains the blood from all the organs of digestion containing digestive end productsThe hepatic artery delivers oxygenated blood to the liverThe blood leaves the liver through the hepatic veins to the inferior vena cavaLiver lobulesLiver lobules: The liver contains thousand of liver lobules which are the functional unit of the liverLiver lobules consist of a special arrangement of blood vessels and hepatic cellsThere is a central vein with rows of hepatic cells surrounding itThe hepatic cells are bathed with blood that enter the lobule from the hepatic artery and portal veinBlood from these two blood vessels mixes in the liver in spaces called sinusoidsThe hepatic cells extract water and dissolved substances from the sinusoidal bloodThe hepatic cells then secrete bile into the tiny canals called canaliculiThese tiny bile canals merge with the canals from other lobules to form larger hepatic bile ductsBile exits the liver through the hepatic bile ductsBile Bile: Green-yellow secretion produced by the liver and stored in the gallbladder800-1000 ml is secreted in 24 hoursComposed of water, electrolytes, cholesterol, bile pigments and bile saltsBile pigments bilirubin and biliverdin are formed from the hemoglobin of old RBCsBile salts are more abundant and aid in digestion of fat and absorption of fat-soluble vitamins and give stool its brownish color

Absence of bile salts due to gallbladder disease cause clay colored stool or gray45Biliary TreeBiliary tree:The ducts that connect the liver, gallbladder, pancreas and duodenum are called the biliary treeNetwork of ducts which include the:Hepatic bile ducts: receives bile from the canaliculi within the liver lobulesCystic duct merges with the hepatic duct to form the common bile ductThe common bile duct carries both the hepatic ducts and cystic ducts to the duodenumThe base of the common bile duct swells to form the ampulla of Vater (hepatopancreatic ampulla) which is the site the main pancreatic duct joins the common bile ductThe sphincter of Oddi (hepatopancreatic sphincter) encircles the base of the ampulla where it enters the duodenumThe sphincter of Oddi is controls the release of bile to the duodenum and is sensitive to nervous, hormonal and pharmacologic controlGallbladder Gallbladder:Pear-shaped sac attached to the underside of the liverThe cystic duct connects the gallbladder with the common bile ductBile produced in the liver, flows through the hepatic ducts, cystic ducts and gallbladderGallbladder concentrates and stores approx. 1.2 liters/dayThe fat in the duodenum stimulates the release of cholecystokinin (hormone) into the blood which travels to the gallbladder causing the smooth muscle of the gallbladder to contractThe contraction of the smooth muscle cause the ejection of bile into the cystic duct then the common bile duct and duodenumPancreas Pancreas Accessory organ of digestion located just under the stomachThe head of the pancreas rests in the curve of the duodenum and the tail is near the spleen in LUQ of abdomenThe main pancreatic duct travels the length of the pancreas and joins the common bile duct at the ampulla of VaterThe pancreatic duct carries digestive enzymes from the pancreas to the duodenum which is the meeting point for digestionPancreas The pancreas secretes endocrine and exocrine substancesExocrine substances include: Pancreatic enzymes, which are the most important digestive enzyme, are secreted by the pancreatic acinar cells in an inactive form and travel through the main pancreatic duct to the duodenumAlkaline substances, rich in bicarbonate, neutralize the highly acidic chyme coming out of stomach and entering the duodenumDigestive enzymes in the duodenum work best in an alkaline environmentPancreas Endocrine substances:Secretion of digestive enzymes and bicarbonate are controlled by nervous and hormonal controlThe presence of food in the stomach and duodenum is the stimulus for nervous and hormonal responseThe presence of chyme in the duodenum stimulates the release of cholecystokinin (CCK) from the duodenal wallsCCK travels in the blood to the pancreas stimulating the release of pancreatic digestive enzymesThe acid in the duodenum stimulates the release of a second hormone, secretin, from the duodenal wallsSecretin travels through the blood to the pancreas stimulating the release of alkaline (bicarbonate) secretions

Digestion & AbsorptionPrimary role of the digestive system is the breaking down of food into particles suitable for absorptionFood is digested mechanically and chemicallyMechanical digestion occurs by chewing in the mouth and mixing and churning activities of muscles in the digestive organsChemically it occurs by chemical changes in response to digestive enzymesChemical digestion refers to a change in the chemical composition of the food moleculeFood is made up of carbohydrates, proteins and fatsDigestive enzymes and several digestive agents (mucus, HCl, and bile) play key role in digestionSpecific enzymes digest each food typeCarbohydrates & EnzymesCarbohydrates are organic compounds composed of carbon, hydrogen and oxygen

Classification includes:Monosaccharides: single sugarsGlucosefructosegalactose Disaccharides: double sugarsSucroselactosemaltose Polysaccharides: many glucose molecules togetherStarches are polysaccharidesCarbohydrates & EnzymesPolysaccharides are digested in two stages:Amylases: an enzyme breaks polysaccharide into disaccharideSalivary amylase and Pancreatic amylaseDisaccharidase breaks diasaccharides into monosaccharidesSucraselactasemaltase Disaccharides are broken down in the duodenum on the surface of the intestinal villus where disaccharidase is secreted and is immediately absorbed into the blood capillariesCellulose, a carbohydrate, cannot be digested and provides fiber and bulk to the stoolProtein & EnzymesProtein is comprised of amino acidsSeveral amino acids linked together form a peptideProteins are very long peptide chainsIn order to be digested these chains must be broken down into small peptides and amino acidsProtease, or proteolytic enzymes is the enzyme that digests proteinsProtease is secreted by 3 organs:Stomach secretes pepsinIntestinal cells secrete enterokinasePancreas secretes trypsin and chymotrypsinmost potent proteaseProtein & EnzymesProteins are broken down into amino acids and absorbed across the intestinal villi into the blood capillariesHydrochloric acid aid in digestion of protein byUnraveling strands of protein making them more sensitive to protease Activating gastric proteolytic enzyme, pepsinogen into pepsin - pepsin facilitates breaking protein into small peptidesFat & EnzymesFats are long chain molecules composed of carbon, hydrogen and oxygenLipase is the enzyme that digests fatsPancreatic lipase is the most importantEnd product of fat digestion is fatty acids and glycerolFat is absorbed into the lacteals of the villusBile aids in the digestion of fat because they are not soluble in water so they clump together forming fat globulesBile breaks down these fat globules into tiny fat globules in a process called emulsificationLipase can work on the surface of the tiny globules digesting fatBile salts aid in 2 ways:Prevent fatty acid from reforming into large fat globulesHelps in absorption of fat soluble vitamins A, D, E, K

EnergyCalorie The amount of energy required to raise 1 gram of water 1 degree Celsius

A Kilocalorie or large calorie is the amount of energy required to raise 1 Kilogram of water 1 degree Celsius

Most of the time when we refer to calories we are referring to kilocalories

As you AgeDigestive tract looses tone, peristalsis slowsSaliva and digestive enzyme secretion slows impairs absorptionSensations of taste and smell diminishLoss of teeth affect chewing ability and food choicesWeakened gag reflex increases chance of aspirationLiver shrinks and receives smaller blood supply decreases filtration and rate of detoxification of blood