Digestive System

Digestive (GI) Tract

General arrangement of abdominal GI organsPeritoneumParietal peritoneumVisceral peritoneumPeritoneal cavityIntraperitoneal organsRetroperitoneal organsMesentariesDouble layered folds of peritoneumGreater omentumLesser omentumMesentery properSuspends small intestine from posterior wall of abdomenMesocolonSuspends large intestinePeritoneal ligamentPeritoneum that attaches one organ to another

Actions of Digestive (GI) TractIngestionOccurs when material enters via the mouthMechanical ProcessingCrushing / Shearing makes material easier to move through the tractDigestionChemical breakdown of food into small organic compounds for absorptionSecretionRelease of water acids, buffers, enzymes & salts by epithelium of GI tract and glandular organsAbsorptionMovement of organic substrates, electrolytes, vitamins & water across digestive epitheliumExcretionRemoval of waste products from body fluids

General Histology of GI Organsfrom the esophagus through the large intestinea tubecomposed of four concentric layers called tunics. From deep to superficial, these tunics are: the mucosathe submucosasubmucosal nerve plexus (Meissner plexus) the muscularismyenteric plexus (Auerbach plexus)the adventitia or serosa

Totalitatea organelor n care are loc transformarea alimentelor n substane simple, asimilabile, formeaz sistemul digestiv.La om, ca i la mamiferele despre care ai nvat anul trecut, sistemul digestiv este alctuit din tubul digestiv i glandele anexe.

Tubul digestiv este alctuit, la rndul lui, din: cavitatea bucal, faringele, esofagul, stomacul, intestinul subire, intestinul gros. Comunicarea cu mediul extern se realizeaz prin dou orificii: gura i anusul.

Cavitatea bucal are n partea anterioar buzele, posterior- valul palatin i omuorul, lateral- obrajii, n partea inferioara- podeaua acoperit de limb, iar planeul bucal formeaz cerul gurii.

Cavitatea oral Opens to outside to facilitate feedingAids in preparation of food for digestionFoods are broken down mechanically by chewing Saliva is added as a lubricant from the auxiliary saliva glandsSaliva contains amylase, an enzyme that digests starchServes as an organ for speech and pleasureIncludes cheeks, lips, tongue, palate, teeth primary & secondary

Cavitatea oral OROPHARYNXLARYNGOPHARYNX

Cavitatea oral 26-*Two regions of the oral cavityVestibule is the space between the cheeks or lips and the gums. Oral cavity proper. The lateral walls are formed by the cheeks.Contain buccinator musclesLips (labia).Orbicularis oris muscleKeratinized stratified squamous ET Gingivae, or gums.Dense regular CTNonkeratinized ETLabial frenulum.

PalatulHard palateAnterior two-thirds of the palatehard and bonySoft palatePosterior one-thirdsoft and muscularprimarily composed of skeletal muscle.Extending inferiorly from the posterior part of the soft palate is the uvula.When swallowing, the soft palate and the uvula elevate to close off the opening of the nasopharynx. Fauces represent the opening between the oral cavity and the oropharynx. Fauces are bounded by paired muscular folds:glossopalatine arch (anterior fold) pharyngopalatine arch (posterior fold)Palatine tonsils are housed between the arches.

LimbaAn accessory digestive organFormed from:skeletal musclecovered with lightly keratinized stratified squamous epithelium. Manipulates and mixes ingested materials during chewingForms the bolus.a globular mass of partially digested material Performs important functions in swallowingInferior surface of the tongueattaches to the floor of the oral cavityBy the lingual frenulum.Numerous small projections (papillae) cover the superior (dorsal) surface.Posterior surface contains lingual tonsils. Skeletal muscles move the tongue.

Papilele lingualeFiliform papillae are the smallest and most numerous. They are aligned in parallel rows. These papillae aid in licking and provide friction for moving food by the tongue.Fungiform papillae are scattered over the tongue surface. They have a vascular core that gives them a reddish hue. Also, they house taste buds.Vallate papillae are in V shaped row at the back of the tongue. They have bitter receptors.

Dinii aflai napoia buzelor, sunt nfipi n oasele celor dou maxilare, n nite caviti numite alveole. Un om adult are 32 de dini, care nu au aceeai form, datorit rolului diferit pe care l ndeplinesc.

DentiiaIncisors (8) for biting food Canines (4) - for grasping and tearing foodBicuspids (8) for grinding and crushing foodMolars (12) for grinding food

Astfel, pe fiecare jumtate de maxilar se gsesc:doi incisivi, cu rol de tiere a alimentelor (I)un canin, cu rol de sfiere a hranei (C)doi premolari, care au dou ridicturi (PM)trei molari, cu patru ridicturi (M)Premolarii i molarii (mselele) au rol n mcinarea alimentelor.Formula dentar a unui om adult este urmtoarea:

Un dinte se compune din trei pri: coroana, coletul (zona de trecere spre rdcin) i rdcin.n seciune longitudinal se observ smaltul care acoper coroana, dentina se afl sub smalt i cementul care acoper rdcin.Pulpa dentar este o cavitate central aflat sub dentina. Aceasta se continu n rdcini, prin canale strbtute de vase sangvine i de nervi care trec prin vrful perforat al rdcinilor spre alveola dentar.

n cursul vieii sale, omul are dou dentiii succesive: dentiia de lapte (20 de dini), numit aa deoarece se dezvolt cnd hrana principal a copilului este laptele, i dentiia definitiv, pe care omul o are ncepnd de la vrsta de 6-7 ani i pn la sfritul vieii. Examinnd radiografia reprodus n figur putei constata cum se produce schimbarea dinilor de lapte cu cei definitivi.

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Glandele salivare

Glandele salivareCollectively produce and secrete saliva. a fluid that assists in the initial activities of digestion Volume of saliva secreted daily ranges between 1.0 and 1.5 L. Most is produced during mealtimeSmaller amounts are produced continuously to ensure that the oral cavity remains moist.FunctionsMoisten foodFood molecules into solution: tasteForm bolus: for swallowingCleanse oral cavity.

Glandele salivareComposition of saliva1. 97-99% water with a pH of 6.7-72. Electrolytes mainly Na+, K+, Cl-, PO4- , HCO3-3. Salivary amylase4. Mucin5. IgA antibodies, lysozyme, defensins

Control of salivationParasympathetic division of ANS control the extrinsic glands. Uses both pressure and chemoreceptors, to stimulate the salivatory nuclei in the medulla. Action potentials return to the extrinsic salivary glands via cranial nerves VII, and IX. The salvia released is serous containing salivary amylase.Sympathetic division of ANS causes the release of a thick mucin rich salvia, and inhibits the release of serous salvia. This results in a dry mouth.

Glanda parotidLargest salivary glands. located anterior and inferior to the earpartially overlying the masseter muscle. Produce about 2530% of salivaconducted through the parotid duct to the oral cavity.

Glandele submandibulareInferior to the body of the mandible.Produce most of the saliva (about 6070%). ducts opens through a papilla in the floor of the mouthlateral to the the lingual frenulum.

Glandele sublingualeInferior to the tongueinternal to the oral cavity mucosa.Each gland has multiple tiny sublingual ductsopen onto the inferior surface of the oral cavityposterior to the submandibular duct papilla. Contribute only about 35% of the total saliva.

Faringele

aflat n continuarea cavitii bucale- are form de plnie; locul n care se ntlnesc calea respiratorie cu calea digestiva i n care se deschid trompele lui Eustachio.

Faringele

The pharynx is divided into three regions. The nasopharynx, oropharynx, and the laryngopharynx.

The mucosa is composed of stratified squamous epithelium which is supplied with mucus producing glands.

Faringele

The external muscle layer consists of 2 skeletal muscle layers. The internal layers run longitudinally. The outer layer encircles the wall of the pharynx. Contractions of these muscles propel food into the esophagus.

Esofagul

tub lung de 20-25 cm, aflat n continuarea faringelui. se deschide n stomac prin orificiul cardia. Peretele sau este format n cea mai mare parte din muchi netezi.

EsofagulThe esophagus is a muscular tube about 25 cm long which connects the pharynx with the stomach. The esophagus takes a straight course through the mediastinum of the thorax and pierces the diaphragm at the esophageal hiatus to enter the abdomen and the stomach.

Esofagul

Esofagul

Stomacul o parte dilatat a tubului digestiv, cu o capacitate de circa 1500 cm3, situat sub diafragm, n partea stng.Stomacul are forma literei J. trecerea spre intestinul subire se face prin orificiul pilor, care este prevzut cu un sfincter; acesta se deschide n momentul n care lasa alimentele s nainteze spre intestin. Peretele stomacului este alctuit din trei straturi de muchi, iar interiorul su este cptuit de mucoasa gastric, n grosimea creia se gsesc glande care secret sucul gastric.

Stomacul Major Functions of the StomachStorage of ingested foodMechanical breakdown of ingested foodDisruption of chemical bonds in food material by acid and enzymesProduction of intrinsic factor, a glycoprotein required for absorption of vitamin B12 in small intestine

Stomacul

StomachGross anatomyCardiaCardiac orificeFundusBodyPylorusPyloric sphincterPyloric orificeGreater curvatureGreater omentumLesser curvatureLesser omemtumGastric folds (rugae)

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*Stomacul

Stomacul

1. MUCOUS NECK CELLS--mucin2. PARIETAL CELL--HCl, and intrinsic factor3. CHIEF CELLS--pepsinogen4. ENTEROENDOCRINE CELLSgastrin, histamine, serotonin, cholecystokinin, and somatostatin.

Digestia gastricStomach performs preliminary digestion of proteins by pepsinSome digestion of carbohydrates (by salivary amylase)Lipids (by lingual lipase)

Stomach contentsBecome more fluidpH approaches 2.0Pepsin activity increasesProtein disassembly begins

Although digestion occurs in the stomach, nutrients are not absorbed there

Intestinul subirede circa 8 m lungime, se ndoaie, formnd cute. n peretele su se gsesc dou straturi de muchi, iar n interior este cptuit cu mucoasa intestinal n care se afl glande care secret sucul intestinal. Mucoasa intestinal prezint numeroase cute pe care sunt situate mici proeminene, numite viloziti intestinale, cu o nlime de 0,5 mm

Intestinul subireFinishes chemical digestionResponsible for absorbing most of the nutrients. Ingested nutrients spend at least 12 hours in the small intestine.thin-walled tubeabout 6 meters (20 feet) in length. coiledExtends from the pylorus of the stomach to the cecum of the large intestineoccupies a significant portion of the abdominal cavity. The duodenumfirst segment of the small intestine. approximately 25 centimeters (10 inches) longoriginates at the pyloric sphinctermajor duodenal papillaThe jejunummiddle region of the small intestine. approximately 2.5 meters (7.5 feet)makes up approximately two-fifths of the small intestines total length. primary region for chemical digestion and nutrient absorption The ileum is the last region of the small intestine. about 3.6 meters (10.8 feet) in lengthforms approximately three-fifths of the small intestine. terminates at the ileocecal valvesphincter that controls the entry of materials into the large intestine.

Cutele i vilozitile mresc considerabil suprafaa de contact cu alimentele. n viloziti se afla capilare sangvine i un vas limfatic. Partea intestinului, lung de circa 25 cm, aflat n prelungirea stomacului se numete duoden. n curbura ase adpostete capul pancreasului.Intestinul subire

Intestinul subire90% of absorption occurs in the small intestine

Intestinul subireThe Duodenum The segment of small intestine closest to stomach25 cm (10 in.) longMixing bowl that receives chyme from stomach and digestive secretions from pancreas and liverFunctions of the duodenum To receive chyme from stomachTo neutralize acids before they can damage the absorptive surfaces of the small intestine

Intestinul subireThe bile duct and the pancreatic duct join to form the hepatopancreatic ampulla which opens into the duodenum.DUODENUMHEPATOPANCREATICAMPULLAMAJOR DUODENAL PAPILLA

Intestinul subireThe Jejunum Is the middle segment of small intestine2.5 meters (8.2 ft) longIs the location of mostChemical digestionNutrient absorptionHas few plicae circularesSmall villiThe IleumThe final segment of small intestine3.5 meters (11.48 ft) long Ends at the ileocecal valve, a sphincter that controls flow of material from the ileum into the large intestine

Intestinul subireIntestinal SecretionsWatery intestinal juice1.8 liters per day enter intestinal lumenMoisten chymeAssist in buffering acidsKeep digestive enzymes and products of digestion in solutionIntestinal MovementsChyme arrives in duodenumWeak peristaltic contractions move it slowly toward jejunumMyenteric reflexesNot under CNS controlParasympathetic stimulation accelerates local peristalsis and segmentation

Intestinul subireThe small intestine is highly adapted for absorption. Its length, together with its plicae circulares, villi, and microvilli amplify its surface area enormously.The plicae circularies are deep permanent folds of the mucosa and submucosa. Villi are fingerlike projections of the mucosa. The epithelial cells of the villi are absorptive columnar cells. In the core of each villus is dense capillary bed and a lymph capillary the lacteal.

Intestinul subireMicrovilli, tiny projections of the plasma membrane of the absorptive cells of the mucosa, give the mucosal surface a fuzzy appearance called the brush border.The cells of the microvilli include simple columnar epithelial cells, goblet cells, scattered enteroendocrine cells, and T cells. The plasma membrane of the epithelial cells have enzymes called brush border enzymes which complete the digestion of carbohydrates and proteins.Between the villi, the mucosa is studded with pits that lead into tubular intestinal glands called intestinal crypts.The epithelial cells that line these crypts secrete intestinal juice. The intestinal juice is a waterly mixture containing mucus that serves as a carrier fluid for absorbing nutrients from chyme.

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Coordination of Secretion & AbsorptionIntestinal Absorption It takes about 5 hours for materials to pass from duodenum to end of ileum Movements of the mucosa increases absorptive effectivenessStir and mix intestinal contentsConstantly change environment around epithelial cells

Intestinul groshorseshoe shaped Extends from end of ileum to anusLies inferior to stomach and liverFrames the small intestineAlso called large bowel Is about 1.5 meters (4.9 ft) long and 7.5 cm (3 in.) wideprezint n partea dreapt a abdomenului o poriune numit cecum, la captul creia se afla o mic prelungire, apendicele. Restul intestinului, numit colon, are forma literei U, cu deschiderea n jos. Partea sa terminal, numit rect, se deschide prin anus, nchis cu un sfincter.

Intestinul grosReabsorption of water Compaction of intestinal contents into fecesAbsorption of important vitamins produced by bacteriaStorage of fecal material prior to defecation

Intestinul grosThe CecumIs an expanded pouch Receives material arriving from the ileumStores materials and begins compactionAppendixAlso called vermiform appendixIs a slender, hollow appendage about 9 cm (3.6 in.) longIs dominated by lymphoid nodules (a lymphoid organ)

Intestinul grosColon:liquid residue mainly water with undigested materalwater is absorbed, bacterial fermentation takes place feces are formed.Has a larger diameter and thinner wall than small intestine The wall of the colonForms a series of pouches (haustra)Haustra permit expansion and elongation of colon

Intestinul grosAscending Colon Begins at superior border of cecum Ascends along right lateral and posterior wall of peritoneal cavity to inferior surface of the liver and bends at right colic flexure (hepatic flexure)Transverse ColonCrosses abdomen from right to left; turns at left colic flexure (splenic flexure)Is supported by transverse mesocolonIs separated from anterior abdominal wall by greater omentumThe Descending Colon Proceeds inferiorly along left side to the iliac fossa (inner surface of left ilium)Is retroperitoneal, firmly attached to abdominal wall The Sigmoid Colon Is an S-shaped segment, about 15 cm (6 in.) longStarts at sigmoid flexureLies posterior to urinary bladderIs suspended from sigmoid mesocolonEmpties into rectum

Intestinul grosThe RectumForms last 15 cm (6 in.) of digestive tractIs an expandable organ for temporary storage of fecesMovement of fecal material into rectum triggers urge to defecate The anal canal is the last portion of the rectumContains small longitudinal folds called anal columns AnusAlso called anal orificeIs exit of the anal canalHas keratinized epidermis like skin

Movements of the Large IntestineGastroileal & gastroenteric reflexesMove materials into cecum while you eatMovement from cecum to transverse colon is very slow, allowing hours for water absorption Peristaltic waves move material along length of colonSegmentation movements (haustral churning) mix contents of adjacent haustra

Movements from transverse colon through rest of large intestine results from powerful peristaltic contractions (mass movements)Stimulus is distension of stomach and duodenum; relayed over intestinal nerve plexusesDistension of the rectal wall triggers defecation reflexTwo positive feedback loopsBoth loops triggered by stretch receptors in rectum

The colon mucosa is simple columnar epithelium except in the anal canal where it is stratified squamous epithelium. There are no circular folds and a reduced number of villi. The mucosa is thicker, with a larger number of globet cells.Intestinul gros

Intestinul gros

Intestinul grosThe last segment of the large intestine is the anal canal. The anal canal is about 3 cm long. It begins where the anus penetrates the pelvic floor and it opens to the body exterior at the anus. The anal canal has 2 sphincters, an internal and external. It is lined with stratified squamous epithelial tissue.

DigestionDigestive system handles each nutrient differentlyLarge organic moleculesMust be digested before absorption can occurWater, electrolytes, and vitaminsCan be absorbed without processingMay require special transport Digestive Enzymes Break molecular bonds in large organic moleculesCarbohydrates, proteins, lipids, and nucleic acidsIn a process called hydrolysisAre divided into classes by targetsCarbohydrases break bonds between simple sugarsProteases break bonds between amino acidsLipases separate fatty acids from glyceridesWater AbsorptionCells cannot actively absorb or secrete waterAll movement of water across lining of digestive tractInvolves passive water flow down osmotic gradients

Role of Fiber in Digestion Fiber is found mostly in plantThere are two types insoluble fiber and soluble fiber Insoluble fiber is a type of fiber which cannot be dissolved in waterInsoluble fiber draws water to the intestine, increasing the bulk and softness of waste productsSoluble fiber which can be dissolved in water Soluble fiber can be digested slowly and it slows the digestive process and keeps the stomach fuller longer leaving the body feeling full for a longer period of time Digestion and absorption of carbohydrates are slower so that glucose (sugar) in food enters the bloodstream more slowly, which keeps blood sugar on a more even levelThe slow absorption of sugar gives the body an opportunity to regulate blood sugar levels

Histological Structure of the Digestive (GI) Tract

Movement of Digestive MaterialsBy muscular layers of digestive tractConsist of visceral smooth muscleAlong digestive tract:Has rhythmic cycles of activities (PERISTALSIS)Consists of waves of muscular contractionsMove a bolus along the length of the tractControlled by pacesetter cellsSurrounding the lumen of the tractCells undergo spontaneous depolarizationTriggering wave of contraction through entire muscular sheet

Peristaltism

DIGESTIVE PROCESS Ingestion intake of food Digestion breakdown of food bit by bit into molecules small enough to be absorbed Mechanical Digestion physical breakdown of food Chemical Digestion chemical breakdown of macromolecules to monomers Absorption transport of productions into the blood Elimination (Defecation) - elimination of undigested waste

CHEMICAL DIGESTION CARBOHYDRATESPROTEINFATSNUCLEIC ACIDS

Common Disorders of Digestive System Stomach and duodenal ulcersCancers of the digestive systemDiarrheaLactose Intolerance Hepatitis Crohns Disease, GERD, Diverticular Disease, Celiac Disease (National)

Sfrit

**************************Regions of the StomachCardiaFundus BodyPylorus Constantly being replaced, covered thick mucus, same simple columnar epitheliumPyloric Sphincter regulates gastric emptying

Gastric GlandsIn fundus and body of stomachExtend deep into underlying lamina propriaEach gastric pit communicates with several gastric glandsParietal cells Chief cellsParietal CellsSecrete intrinsic factor and hydrochloric acid (HCl)Chief CellsSecrete hydrochloric acid (HCl)Are most abundant near base of gastric glandSecrete pepsinogen (inactive proenzyme)PepsinogenIs converted by HCl in the gastric lumenTo pepsin (active proteolytic enzyme)

*************Secretin Is released when chyme arrives in duodenumIncreases secretion of bile and buffers by liver and pancreasCholecystokinin (CCK) Is secreted in duodenumWhen chyme contains lipids and partially digested proteinsAccelerates pancreatic production and secretion of digestive enzymesRelaxes hepatopancreatic sphincter and gallbladderEjecting bile and pancreatic juice into duodenum Gastric Inhibitory Peptide (GIP) Is secreted when fats and carbohydrates enter small intestineVasoactive Intestinal Peptide (VIP)Stimulates secretion of intestinal glandsDilates regional capillariesInhibits acid production in stomachGastrin Is secreted by G cells in duodenumWhen exposed to incompletely digested proteinsPromotes increased stomach motilityStimulates acids and enzyme productionEnterocrininIs released when chyme enters small intestineStimulates mucin production by submucosal glands of duodenum

*Functions of the Large IntestineReabsorption of water Compaction of intestinal contents into fecesAbsorption of important vitamins produced by bacteriaStorage of fecal material prior to defecation

*******The Processing and Absorption of NutrientsBreaks down physical structure of foodDisassembles component molecules Molecules released into bloodstream areAbsorbed by cellsBroken down to provide energy for ATP synthesisOr used to synthesize carbohydrates, proteins, and lipids

*The MucosaIs the inner lining of digestive tractIs a mucous membrane consisting ofEpithelium, moistened by glandular secretionsLamina propria of areolar tissueThe Digestive Epithelium Mucosal epithelium is simple or stratifiedDepending on location, function, and stresses: oral cavity, pharynx, and esophagus:mechanical stresseslined by stratified squamous epitheliumstomach, small intestine, and most of large intestine:absorptionsimple columnar epithelium with mucous (goblet) cellsThe Digestive Epithelium Enteroendocrine cellsAre scattered among columnar cells of digestive epitheliumSecrete hormones that:coordinate activities of the digestive tract and accessory glands

*Peristaltic MotionCircular muscles contract behind bolus:While circular muscles ahead of bolus relaxLongitudinal muscles ahead of bolus contract:Shortening adjacent segmentsWave of contraction in circular muscles:Forces bolus forward

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