Chapter 3- DIGESTION, ABSORPTION, AND TRANSPORT3.1 digestionA. digestion overview1. the bodys way of breaking down food into nutrients in preparation for absorption2. challenges of digestion:a. throat must be arranged so food and swallowing don’t interfere each otherb. 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 consistencyd. 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 intervalsB. anatomy of the digestive tract1. gastrointestinal tract: flexible muscular tube that extends from mouth, esophagus, stomach, small intestine, large intestine, rectum, and finally to the anus2. moutha. process of digestion begins in the mouthb. fluids dissolve foods so we can taste themc. basic taste buds:- sweet- sour- bitter- saltyd. tongue moves food and pushes the food back to the pharynx- short tube that is shared by both the digestive and respiratory systeme. to bypass lungs – epiglottis closes off airwayf. after mouthful of food is chewed and swallowed it is called a bolus3. esophagusa. 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. stomacha. retains the bolus in its upper portion – bit by bit it goes down to lower portionb. adds juices – grinds it – now a semiliquid mass called chimec. chime goes through pyloric sphincter, which opens to the small intestine5. small intestinea. common bile duct drips fluid into small intestine- from gallbladder and pancreas b. cyme goes through three segments:- duodenum- jejunum- ileum6. large intestine (colon)a. chime goes through another spinchter- ileocecal valve – beginning of colonb. chime passes the appendixc. goes to rectum- as it passes the rectum the colon withdraws waterd. goes through last 2 sphincters of the anusC. the muscular action of digestion1. peristalsisa. action of the rings in the GI tract tightening and the long muscles relax b. pushes food downward 2. stomach actiona. 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 musclesc. 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 3. segmentation a. circular muscles of intestines contract and squeeze – called segementation4. 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 glandsb. stomachc. pancreasd. 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. enzymesa. protein that facilitates a chemical reaction – making a molecule, breaking apart a molecule, changing/exchanging molecules b. acts as a catalyst - enzyme itself remains unchangedc. hydrolysis - facilitated by enzymes in digestion- addition of water to break a molecule into common digestive enzymesd. enzymes end in –ase4. salivaa. 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 carbs5. 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 begunb. 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 pH7. bilea. bile flows in duodenum b. liver continuously produces bile; stored in gallbladderc. not an enzyme; it’s an emulsifier that brings fat into suspension in water so enzymes can break them downE. 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 system1. small intestinea. 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 cells1. villi recognize and select the nutrients the body needs and regulate their absorption 2. specialized cellsa. specialized to absorb different nutrients; nutrients that are ready for absorption are absorbed at the top of GI tract3. food combininga. idea that certain foods cannot be eaten together is a myth4. preparing nutrients for transporta. 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 liverb. 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 systemA. the vascular system1. vascular = blood circulatory systema. closed system of vessels through which blood flows continuouslyb. the heart serves as the pump2. all body tissues derive nutrients and oxygen from the blood and deposit CO2 and wastes back into the blood a. digestive system provides nutrientsb. lungs exchange oxygen and CO2c. 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
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