Digestion

Day 2 Stomach-LiverDigestionStomachJ-shaped organFound in upper left portion of abdom. cavityCan hold 1 Liter or moreContains thick folds in lining called RUGAEFunctions:Receives food from esophagusMixes food with gastric juicesInitiates protein digestionCarries on limited absorptionMoves food into small intestines

Parts of the StomachFour PartsCardiaSmall area near esophageal openingFundusBalloons superior to cardia and is a temporary storage areaBodyMain part of stomach, found between fundus and pylorusPylorusNear small intestine, narrows to form pyloric canalPyloric SphincterValve that controls gastric emptying

Gastric SecretionsMucous membrane forms inner liningContains gastric pits which lead to gastric glandsGastric Glands produce three types of secretions known as GASTRIC JUICEMucous cellsFound near opening of glands, produce mucusChief CellsFound deeper in glands, produce digestive enzymesParietal CellsFound deep in glands, produce HCL (Hydrochloric Acid)

Gastric JuicesPepsinMost important digestive enzymeProduced by chief cellsForms when PEPSINOGEN contacts HCLBreaks down proteinMucous Cells*Forms a alkaline secretion that covers inner surface of stomach wall*Prevents stomach from digesting itself

Gastric Juices Cont.Intrinsic FactorSecreted by parietal cellsHelps small intestine absorb vit. B12Regulation of Gastric SecretionProduced continuously, but rate variesControlled neurally and hormonallyThinking of food or food entering stomach causes stimulation of ACH and gastrin which increase secretory activityOnce food enters small intestine, hormone cholecystokinin stimulates decrease in gastric juice productionGastric AbsorptionEnzymes break down proteins but does not absorb muchWhats absorbed:Only small amounts of water and certain salts are absorbedLipid-soluble drugsAlcohol

Mixing and Emptying ActionsChymeProduced after a mealConsists of gastric juices and food particlesSemi fluid pastePeristaltic waves push Chyme towards pyloric sphincterLittle by little Chyme is pushed into small intestinesRate depends on type of food and fluidity of chymeLiquids pass through stomach rapidlyFatty foods remain for 3-6 hours after consumptionHigh protein foods are quicker than fatsCarbs are faster than proteins

http://www.youtube.com/watch?v=URHBBE3RKEsVomitingResults from a complex reflex that empties the stomach in the reverse of the normal direction. Irritation or distension in the stomach or intestines can trigger vomiting. Sensory impulses travel from the site of stimulation to the vomiting center of the Medulla, and motor responses follow. These include taking a deep breath, raising the soft palate and thus closing the nasal cavity, closing the opening to the trachea, relaxing the circular muscle fibers at the base of the esophagus, contracting the diaphragm so it presses downward over the stomach, and contracting the abdominal wall muscles to increase pressure inside the abdominal cavity. As a result, the stomach is squeezed from all sides, forcing its contents upward and out through the esophagus, pharynx, and mouth.Accessory OrgansOnce food leaves the stomach and enters the small intestine accessory organs add digestive juicesPancreasLies horizontal across the posterior abdominal wallCells called pancreatic acinar produce pancreatic juiceSecretions in to small intestine are controlled by hepatopancreatic sphincter

http://www.youtube.com/watch?v=1l2GTGEwZOYPancreatic JuiceContains enzymes that digest carbs, fats, nucleic acids, and proteinsPancreatic amylaseSplits carbsPancreatic lipaseSplits fat moleculesNucleasesBreak down nucleic acid moleculesTrypsin, Chymotrypsin, CarboxypeptidaseSplit proteinsRegulation of Pancreatic SecretionsNervous and Endocrine systems regulate release of pancreatic juicesHormone Secretin Released when chyme enters small intestine to neutralize it

LiverFound in upper right quadrant of abdominal cavity just inferior to diaphragmPacked with blood vesselsStructureLarge right lobe, smaller left lobeHepatic lobules are the functional unitsHepatic sinusoidsVascular channels that receive newly absorbed nutrientsContains phagocytic cells called Kupffer CellsHelp remove bacteria and other foreign particlesContains many hepatic ducts that merge to form common hepatic duct

http://www.youtube.com/watch?v=RsPzIqcVaoYLiver FunctionImportant metabolic activitesCarb metabolismMaintains blood glucoseLipid metabolismFatty acid metabolismMost important is protein metabolismStores glycogen, iron, vitamins A, D, and B12Destroys damaged RBCsRemoves toxic substances such as alcohol and drugsSecretes Bile (Important to Digestion)

Liver DonationsThe liver is unlike most organs in that it can regenerate. Up to 75% of a liver can be destroyed and the organ can regenerate and recover. For this reason, people can donate parts of their livers to people in liver failure, if the tissues of the donor and recipient are compatible.