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Digestive system Purpose reduce food particles to molecules that can be absorbed in the blood Mechanical breakdown of food chewing Chemical breakdown of food Hcl in the stomach enzymes Incomplete digestive system saclike digestive cavity food enters and wastes leave through a single opening Complete digestive system A tube with an opening at each end one for taking in food and one for eliminating Classifications of animals by food they ingest Carnivore animals products Herbivore plant products Omnivore combination of plant and animal products Types of snomachs Monogastrics one simple stomach carnivores and omnivores Ruminants four compartment stomach herbivores can digest high concentrations of fibers use microbial fermentation Ruminant system of capacity 1 Mouth bites and chews 2 Esophagus connection 3 Four compartment stomach rumen reticulum omasum abomasum First two are 85 Rumen largest of four parts filled with bacteria and other microbes converts large amounts of roughage to amino acids The average cow rumen can hold over 40 gallons Bacteria and Protozoa in Rumen moist warm constant supply of nutrients various populations of organisms depending on the kind and quality of the feed acidic environment of abomasum eventually kills the microorganisms provide amino acids and some energy to animal Reticulum 2 gallons in cow Compartment where liquid goes honeycomb in structure interacts with rumen to mix contents Omasum 4 gallons in cow Grinds and squeezes many folds removes some liquid receives food after cud has been chewed Abomasum 4 gallons in cow True stomach enzymes and acids closest to human stomach Ruminants eat rapidly they regurgitate food cud chew it again and swallow exposes more surface area for microbial action Rumination continuous regurgitation chewing and swallowing Monogastric system Mechanical processing and motility physical manipulation that breaks up mixes propels food Secretion Release of digestive enzymes other substances from lining of tract and accessory organs Digestion chemical breakdown of food into molecules small enough to be absorbed Absorption Passage of digested nutrients fluid across the tube wall and into body fluids Elimination Expulsion of undigested unabsorbed residues from the end of the gut Human digestive system Consists of a muscular tube extending from mouth to anus and its associated organs e g salivary glands gall bladder liver pancreas Complete system with many specialized organs 25 30 feet long lined with mucus secreting epithelium movement is one way from mouth to anus Food take roughly 24 hours to go through system Major components Mouth pharynx esophagus gut stomach small intestine large intestine rectum anus Accessory organs Salivary glands Secrete saliva with carbohydrate digesting enzymes buffers mucus to moisten food Liver Secretes bile for emulsifying fat also roles in fat carbohydrate protein metabolism Gallbladder Stores concentrates bile from liver Pancreas 1 secretes digestive enzymes that break down all major food molecules 2 secretes buffers against HCL from stomach 3 secretes insulin to control glucose metabolism Digestion begins in mouth The teeth break up food saliva moistens it And salivary enzymes begin the digestion of starch The tongue pushes the bolus of food into the pharynx Saliva produced by salivary glands almost gallon each day includes Amylase enzyme starts digestion of carbohydrates Bicarbonate buffer mucins bind food into bolus water 99 Swallowing Complex reflex Tongue forces food voluntary action into pharynx common chamber for food and air Epiglottis closes off trachea breathing temporarily ceases Food moves into esophagus muscular tube about 0 8 in diameter moved by wavelike contractions involuntary called peristalsis then through esophageal sphincter into stomach Stomach Dimensions vary can be narrow tube when empty or expanded into a sac that can hold almost 0 5 gallon accordion like folds in muscle wall rugae allow expansion sphincters at both ends control entry and exit of food Functions include a Temporary storage of ingested food b Mixing of ingested food mechanical digestion c Digestion of proteins using acids and enzymes chemical digestion d Absorption of some substances e g alcohol aspirin e Controlling passage of food into small intestine stays in stomach 4 5 hours Digestion by gastric juices Epithelium secretes HCl and enzyme pepsin from glands in gastric pits HCl reduces pH to level suitable for activity of pepsin pepsin begins chemical digestion of proteins Epithelium also secretes mucus which coats inner lining of stomach and protects it from corrosive action of gastric juices Gastric ulcers result when mucus layer breaks down no longer protects from acid Bolus becomes chyme after it leaves the stomach Small interestine duodenum jejunum ileum roughly 25 feet long Most chemical digestion and nutrient absorption is here Receives digested food called chyme from stomach Receives secretions from liver gallbladder and pancreas Walls of small intestine projections into the intestinal lumen increase surface area available for absorption Absorption villi and microvilli line small intestine Surface area size of tennis court Chemical digestion Bicarbonate from pancreas to neutralize stomach acid Enzymes from pancreas digest carbohydrates fats and proteins Bile from liver and gall bladder break up fats Functions of liver Removes and destroys some toxins Serves as large reservoir of blood phagocytes here constantly remove cell debris pathogens and damaged red blood cells Produces bile which aids in digestion of fats Largest internal organ and gland in the body Gallbladder Muscular sac that stores bile produced by liver bile produced in liver may flow directly into small intestine through common hepatic duct as during mealtimes or may back up through cystic duct to be stored in gallbladder Large intestine about 5 feet long 3x wider than small intestine 1 Functions holds and compacts undigested material absorbs water and vitamins produced by resident intestinal bacteria Cystic duct gall bladder Hepatic duct liver Bile duct both E coli bacteria in large interestine Breaks down remaining nutrients Synthesizes vitamins vitamin K Three regions of the large intestine a Cecum expanded chamber receives chyme from small interestine still used in herbivores many bacteria in carnivores it is reduced to appendix Fermentation b Colon longest portion has characteristic series of muscular pouches water is reabsorbed


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NCSU BIO 105 - Digestive system

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