Digestion

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Scoop to Poop
As I’m taking a bite of pizza, I follow it through my digestive tract. It has many stops along the way before finally being able to exit through the other end. First, it goes through my mouth to my pharynx, then to my esophagus, stomach, small intestine, large intestine, and lastly out through my anus. The first stop in the digestive tract is the mouth, or oral cavity. The mouth serves two main functions: the beginning of mechanical and chemical digestion. Chewing, or mastication, breaks the food into smaller pieces and increases the overall surface area so the chemical digestive enzyme, saliva, can begin to work on breaking down carbohydrates. Salivary amylase, the main enzyme in saliva, is secreted by the salivary glands in the mouth and it helps hydrolyze starch into smaller sugars, maltose and dextrin. Lipase is also included in saliva and helps catalyze the hydrolysis of lipids. The tongue then balls up the food into a bolus that is swallowed and moves to the next step. The bolus then travels through the pharynx before reaching the esophagus. The major feature of the pharynx is the epiglottis which prevents food from entering the lungs. The esophagus is a muscular tube that transports the bolus from the pharynx to the stomach for digestion to continue. The rhythmic muscular contractions which push food downward are known as peristalsis and are an involuntary act. The bolus then reaches the muscular ring known as the lower esophageal sphincter, or cardiac sphincter because of its proximity to the heart, where it is then released into the stomach. The stomach is the primary organ in the digestive system. The epithelium of the stomach consists of 3 types of cells: mucous, chief, and parietal. Mucous cells secrete mucous that coats and protects the epithelium from the harsh environment within. Chief cells secret pepsinogen, which is later, converted to pepsin that will digest the bonds in protein. Pepsin is different from most other...
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