Chapter 3 DIGESTION ABSORPTION AND TRANSPORT 3 1 digestion A digestion overview 1 the bodys way of breaking down food into nutrients in preparation for absorption 2 challenges of digestion a throat must be arranged so food and swallowing don t interfere each other b contents of the digestive tract should be kept moving forward slowly but steadily at a pace that permits all reactions to reach completion c must regulate the amount fluids to keep intestinal contents at right consistency d every food particle must be accessible e the digestive enzymes digest CHO PRO and FAT cells of GI tract are made of CHO PRO and FAT cells must be protected from the juices they secrete f waste matter must be excreted at different intervals B anatomy of the digestive tract 1 gastrointestinal tract flexible muscular tube that extends from mouth esophagus stomach small intestine large intestine rectum and finally to the anus 2 mouth a process of digestion begins in the mouth b fluids dissolve foods so we can taste them c basic taste buds sweet sour bitter salty d tongue moves food and pushes the food back to the pharynx short tube that is shared by both the digestive and respiratory system e to bypass lungs epiglottis closes off airway f after mouthful of food is chewed and swallowed it is called a bolus 3 esophagus a has a sphincter muscle at each end upper esophageal sphincter opened during swallowing lower esophageal sphincter at entrance of stomach prevent food from going back up 4 stomach 5 small intestine a retains the bolus in its upper portion bit by bit it goes down to lower portion b adds juices grinds it now a semiliquid mass called chime c chime goes through pyloric sphincter which opens to the small intestine a common bile duct drips fluid into small intestine from gallbladder and pancreas b cyme goes through three segments duodenum jejunum ileum 6 large intestine colon a chime goes through another spinchter ileocecal valve beginning of colon b chime passes the appendix c goes to rectum as it passes the rectum the colon withdraws water d goes through last 2 sphincters of the anus C the muscular action of digestion 1 peristalsis a action of the rings in the GI tract tightening and the long muscles relax b pushes food downward 2 stomach action a has thickest walls and strongest muscles of all the GI tract organs b has standard circular and longitudinal muscles as well as a third layer of diagonal muscles c stomach works to push down pyloric sphincter stops it d when chime is completely liquefied with digestive juices sphincter periodically opens to let small amounts out a circular muscles of intestines contract and squeeze called segementation 3 segmentation 4 sphincter contractions a reflux stomach contents coming back up s topped by lower esophageal sphincter cardiac sphincter D the secretions of digestion 1 the breakdown of food into nutrients requires secretions from 5 different organs a salivary glands b stomach c pancreas d liver via the gallbladder e small intestine 2 these secretions enter the GI tract at various points along the way bringing in water and variety of enzymes 3 enzymes a protein that facilitates a chemical reaction making a molecule breaking apart a molecule changing exchanging molecules b acts as a catalyst enzyme itself remains unchanged c hydrolysis facilitated by enzymes in digestion addition of water to break a molecule into common digestive enzymes d enzymes end in ase 4 saliva a salivary glands squirt just enough saliva to moisten each mouthful of food so it can go down esophagus easily b saliva contains salt water mucus and enzymes that initiate the digestion of carbs 5 gastric juices a gastric glands secrete gastric juices in stomach mixture of water enzymes and HCl acts primarily in protein digestion b mucus secreted by entire lining of GI tract protects cells from acid 6 pancreatic juice and intestinal enzymes a by the time food leaves stomach digestion of all three energy nutrients CHO PRO FAT has begun b pancreatic juice contains enzymes that act on all 3 energy nutrients contain sodium bicarbonate opposite of stomach acid lowers pH of chime now is neutral or slightly alkaline pH a bile flows in duodenum b liver continuously produces bile stored in gallbladder c not an enzyme it s an emulsifier that brings fat into suspension in water so enzymes can break them down 7 bile E the final stage 1 by the time contents reach Go tract reach end of small intestine little remains but water dissolved salts and body secretions and undigested materials such as fiber 3 2 absorption A anatomy of the absorptive system 1 small intestine a villi fingerlike projects increase surface area of small intestine on each individual villi there are hundreds of cells called microvilli between villi crypts tubular glands that secrete the intestinal juices into the small intestine nearby goblet cells secrete mucus constant motion traps nutrients then draws them into the cells B a closer look at the intestinal cells 1 villi recognize and select the nutrients the body needs and regulate their absorption 2 specialized cells a specialized to absorb different nutrients nutrients that are ready for absorption are absorbed at the top of GI tract 3 food combining a idea that certain foods cannot be eaten together is a myth 4 preparing nutrients for transport a when nutrient has crossed the cell of the villus enters bloodstream or lymphatic system water soluble nutrients and smaller products of fat digestion are released directly into the bloodstream and guided to the liver b larger fats and the fat soluble vitamins are insoluble in water and blood is mostly water group together in larger molecules go into lymphatic system bypassing the liver for now 3 3 the circulatory system A the vascular system 1 vascular blood circulatory system a closed system of vessels through which blood flows continuously b the heart serves as the pump 2 all body tissues derive nutrients and oxygen from the blood and deposit CO2 and wastes back into the blood a digestive system provides nutrients b lungs exchange oxygen and CO2 c blood leaves the right side of the heart goes through lungs left side of heart now fully oxygenated left side pumps blood out of aorta through arteries to all systems in the body blood circulates into capillaries then collects in veins right side of heart 3 hepatic portal vein a directs blood to liver not heart b blood leaving liver collects in hepatic vein heart a heart arteries
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