The Magic School Bus
I was in Purdue this past weekend, and I decided to purchase and eat a foot-long Meatball Marinara Sandwich. This sandwich consisted of a 12” Italian bread (10 oz), 8 meatballs (12 oz), 8 slices of American cheese (8 oz), jalapenos (1/4 cup), and lettuce (1 cup). The protein comes from the beef meatballs and sliced American, which have about 4 grams of protein each. The carbohydrates come from the Italian bread (white bread) and the American cheese, and the fat comes from the meatballs. The whole digestion process starts even before the food reaches our mouth as hunger and appetite are two major components of the cephalic phase of digestion, which is the stimulation and release of digestive juices in preparation of the food. Once inside the mouth, my teeth and salivary enzymes help to break down the food components into smaller molecules. This chemical amylase in our mouth helps to start breaking down the food chemically in order to fully be able to absorb all nutrients in the later process. The resulting product after all the food’s been chewed is called the bolus.
This food now starts to travel down to the stomach, but it first passes through the windpipe and in to the esophagus through peristalsis, the wavelike muscle contractions that push the food down the tube. The bolus now enters the stomach, which can expand up to 32 fl oz when full. The brain first signals for the secretion of gastric juices before the bolus gets to the stomach. These gastric juices consist of hydrochloric acid, which denatures proteins and kills harmful bacteria, and gastric lipase, which is responsible for lipid digestion. These juices also start the chemical digestion of proteins and fats. In this next phase of the digestion process, the gastric phase, gastrin is secreted. This increases the secretions of gastric cells, which makes the gastric juices inside the stomach even more acidic. In addition to secreting gastric, the stomach’s muscles...
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