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Peanut Butter and Banana Sandwich Digestion

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Kayla May

on 19 October 2012

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Transcript of Peanut Butter and Banana Sandwich Digestion

A digestion story The Journey of Three Nutrients It’s common knowledge that there isn’t a whole lot of love between bananas, whole wheat bread, and peanut butter, but one autumn day, the three of them were forced to spend time together. They were put together to make a sandwich. The peanut butter, bread, and banana pieces were torn apart by pearly white teeth. While chewing occurred, the protein-rich peanut butter was moistened and mixed with saliva from the salivary glands to prepare for swallowing. The starchy banana and bread were churned with amylase inside the mouth. Even with all the commotion going on, the peanut butter managed to hear the bread call out “Chemical digestion! It’s happening!” In the end, what were once starches were now polysaccharides and maltose. The fibre from the bread and banana though, were still in tact. “You’re all fat!” said the banana to the peanut butter. The peanut butter defended himself saying “Everyone needs a little fat.” The sandwich remained together on a counter overnight, and surprisingly, after a few hours, the banana, the bread and the peanut butter started to get along with one another. At noon the next day, the sandwich parts said their goodbyes because they knew what was in the near future: ingestion. Piece by piece the sandwich disappeared into the mouth of its consumer. Chomp! Chomp! Chomp! “And so digestion begins!” said the bread. Everyone involved in the sandwich had some knowledge of the process of digestion and even though it seemed a little scary, they had agreed that it would probably be a great experience. The now smaller food particles fell down the back of the throat. Pieces of the banana pointed out the way to the trachea, but the epiglottis forced the food to continue on to the esophagus instead. “Move along please,” he ordered. The sandwich pieces started feeling a little queasy as peristalsis started. Contraction after contraction in a wave-like motion moved the food down the esophagus. There was no turning back now. The sandwich pieces knew that their shared time together was limited so they stayed close and cherished all of it. After being brutally pushed by the cardiac sphincter, the sandwich pieces now occupied the stomach. Polysaccarides complained “Man, oh man it’s acidic in year.” Pepsin, one of the proteases, along with hydrochloric acid, rushed over to the peanut butter proteins, denaturing them until they were broken up into polypeptides -smaller chains of amino acids. “My turn,” said the peanut butter fats. As pepsin worked on the proteins, lipase came into the scene. The stomach turned and contracted, and the fats were mixed with water, stomach acids, and lipase, which broke down the triglycerides into diglycerides and fatty acids. Finally, more amylase worked hard to break the small polysaccharide chains into disaccharides. Lipase The fibres, still remaining whole, felt superior to the others in surviving the trip thus far. The bonds in the fibre molecules just couldn’t be broken. “Can’t touch this!” they bragged. Contrary to what the tiny sandwich pieces thought, their journey was not over. In fact, there were still lots of breakdown activities to come. Fat, protein, fibre and simple sugar particles squeezed though the pyloric sphincter and passed into the duodenum, which lead them to the small intestine. This was where the real fun went down! Bile, bile, and more bile came pouring out of the nearby gall bladder. “That’s from the liver,” it said. “Bile is the first step in breaking you fats down!” The ends of the bile molecules that were afraid of water (hydrophobic) got cozy with the diglycerides and absorbed right into them. The other ends of the bile molecules seemed to like the water (hydrophyllic). They stuck out so that the fat particles mixed in well with the surrounding water. Next, out from the pancreatic duct came digestive enzymes, and lots of them. The enzymes from the pancreas seemed to be friends with the gall bladder as they thanked him for the bile. “Let’s get to work guys,” they shouted. The pancreatic and other intestinal enzymes were excited to begin splitting apart polypeptides into tripeptides, dipeptides, and amino acids. Diglycerides were also broken down into single fatty acids. “Bye guys,” said one of the polypeptides, “It was nice knowing you all.” Everyone had really been separated now, and despite their previous disputes, they already missed one another. But back where digestion was still happening, polypeptides were being broken down into smaller and smaller particles, and so were the disaccharides from the bread and the banana. Lactase tore up lactose into galactose and glucose. Maltase ripped one glucose molecule from the other. Sucrase did the honour of separating glucose from fructose. The process was just as intense as it sounds! Now all of the starch molecules were even smaller than before. They became what are known as monosaccharides and they were ready for absorption. Finger-like projections in the small intestine called villi and microvilli aimed to do one thing: absorb. Before being ingested, the banana had wondered what happened to food after it was completely broken down. The villi were her answer. They tried to comfort the food particles by saying, “Don’t be scared. We’re your door to new adventures! We will bring you to the blood stream where you will be pumped around the body to wherever you’re needed”. The villi began sucking up the monosaccharides, making them disappear from the digestive tract forever! Near the end of the small intestine was where everyone else was absorbed. This included the amino acids, single fatty acids, and vitamins that had come along for the ride. Into the large intestine flowed the remains of the food that were not absorbed in the small intestine. The fibre molecules which had found little to no amusement with the process of digestion (aside from feeling proud to have escaped from the many enzymes and stomach acids), now started to attract water molecules. The fibre also held on tightly to some unabsorbed fats and cholesterol while traveling through the large intestine. Liquids were still being absorbed via the intestinal walls, but a lot of it remained in the fibre-rich solid. “We did it!” exclaimed the fibre molecules,” “Who would have thought we would make it?” Though they hadn’t made their way out of the body when they boasted about there triumph, eventually, they did. Rumour has it that even though all of the other nutrients were split apart, they still see each other sometimes, and when they do, they reminisce about their time spent bickering with one another while they were whole foods, but they also acknowledge how pleased they are with their new lives in the body. The End.
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