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TAMU ANSC 303 - Digestive Systems and Digestion V
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ANSC 303 1st Edition Lecture 6Outline of Last Lecture I. Location of Microbesa. Epithelial Cellsb. Fiber Materialc. Rumen FluidII. Rumination and Eructationa. Rumination b. EructationIII. Small IntestineIV. Secretions Entering Small Intestine Outline of Current Lecture I. Small IntestineII. Small Intestine – StructureIII. Secretions in Small IntestineIV. Nutrient Absorption From Small IntestineV. Nutrient Absorptiona. Diffusionb. Facilitated Diffusionc. Active Transportd. Pinocytosis/EndocytosisVI. Large IntestineVII. Gastrointestinal HormonesVIII. Hormonal Control off Digestion Regulatory PeptidesCurrent LectureI. Small Intestine Anatomy A. Enterocyte = single cell layer between blood and foodB. Liver metabolizes most thingsThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.C. Nutrients usually travel through the small intestine, into the blood stream, and then into the liverD. The small intestine is a small hollow tubea Muscle folds the entire way b Small villi line the entire intestinec Absorptive layerII. Small Intestine - StructureA. Lumen - the hollow area in the middle of the small intestineB. Mucosa - the lining of the small intestine; protects enzymes from breaking down the small intestineC. Villi - the entire finger-like structure in the small intestine; increases surface areaD. Crypts - the valley between the villi E. Lacteal - the tree trunk in the middle of the villi F. Enterocyte - the single layer of cells the separates the product in the lumen from the bloodG. Brush border - microvilli that coat the villi H. The new cells start in the crypt and travel to the top of the villi I. One of the highest cell turnover rate III. Secretions Into Small IntestineA. Enzymes and buffers enter early in the small intestineB. Enter via pancreatic ducta Most enter inactively or require co-factors (esp. protein degraders)b Starchesc Dextrind Fatse ProteinsC. Secretes 1.5 to 2 L per day in humansa Enzymes i. Acinar cellsii. Specific cells within pancreasb Bicarbonate bufferi. Centroacinar cellsii. Product from the stomach is highly acidiciii. The pH in the small intestine needs to be neutral D. Controlled by:a Nerve innervation: full vs emptyb Gastrointestinal hormones:i. CCKii. Gastriniii. SecretinE. Livera Synthesizes bileb Bile store in gallbladderi. Sphincter of Oddiii. Bile duct into duodenumc Horses have no gallbladderi. They are limited in the amount of bileii. Bile comes directly from the liverd Bile is used to emulsify fati. Fat is present in fat globulesii. The bile separates the fat globule into single fat compoundsIV. Nutrient Absorption From Small Intestine A. Adsorption occurs from lumen to the enterocyteB. Enterocyte = lipid bilayerC. Most digestion occurs in duodenum D. Absorption = ileum and jejunum E. Goal digestion = make the products small enough for enterocyte to be able to takeF. Goal absorption = product sent to the liverV. Nutrient absorption A. Diffusiona Advantage: no energy neededb Disadvantage: only absorb 50% of the nutrients available c Molecules pass freely through membrane d Moves from high concentration to low concentration e VFAs are transported this wayB. Facilitated diffusiona Uses a carrierb Carrier is specific to what it passesc Fructose is transported this way d Advantage: no energy needede Disadvantage: only absorb 50% of the nutrients available C. Active transporta Advantage: one way, against the concentration gradientb Disadvantage: energy requiredc Carrier loads particle on the outside of celld Carrier released on the inside of the cell e ATP is requiredf Travels in ONE DIRECTIONg glucoseD. Pinocytosis/endocytosisa The membrane gets close to the particleb Particle is engulfedc The particle is spit out on the other sided This is how large particles are movede Fats are moved this wayE. The mechanism used depends on:a Solubility of nutrienti. Fat needs endocytosisb Concentration of electrical gradientc Size of molecule being absorbedVI. Large IntestineA. There is variation among the various speciesB. 3 segments:a Cecum i. Slows particles down to allow more time for fermentation ii. Blind pouch b Colon i. Large intestineii. Small intestineiii. Named according to diameterc Rectum C. Functiona Fermentative digestion i. No enzyme secretions ii. Relies on microbes from small intestineb Absorption of:i. Waterii. VFAiii. Vitaminsiv. Mineralsc NO absorption of:i. Lipidsii. ProteinsD. If the rumen is large, the large intestine is smalla Lose space in one place to gain space in anotherb There is no need for double fermentation E. Monogastric size depends on dieta Herbivores - largeb Carnivores - small F. Hard to have a high population of microbes because the microbes have to make it past the stomach (highly acidic) and the small intestineG. Smaller and different population VII. Gastrointestinal HormonesA. Secretion and motility regulated by nervous system and hormones B. Regulatory: produced by x, acts on xC. Neurocrine: produced by x, acts on the entire bodyD. Polypeptide hormones:a Produced by mucosab Act locally or released into circulationVIII. Hormonal Control off Digestion Regulatory PeptidesName of Peptide Origin Stimulus FunctionGastrin Big pictureorchestratorStomach Abomasum Food in stomach Stimulates HCL and pepsinogen secretionIncreases stomach motility Secretin Duodenum Acid(stomach content is always acidic)Stimulate pancreatic secretions Slows stomach motility and acid productionMotilin2nd peptide to tell thepancreas to startsecreting DuodenumJejunumSimulates gastric and duodenal motility Gastric and pancreatic secretionsGallbladder contractionCholecytokinin (CCK)Sweaty and nervousDuodenum Fat and protein in theduodenumStimulates bile and pancreatic secretionsRegulates appetite and feed uptakeGlucose-dependent Duodenum Fats and biles Stimulates insulininsulinotropicpeptide (GIP)Every cell responds toinsulin; insulin tellsthe body you’re fullJejunum secretionsInhibits stomach motility Secretion of acid and


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TAMU ANSC 303 - Digestive Systems and Digestion V

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