Digestion
You ask how the digestion system works and what happened to that cheeseburger you ate? Think of digestion like disassembly plant. The main organs of digestion form what is called the GI (gastrointestinal) tract. This creates an open tube that runs from the mouth to the anus; just imagine a big water slide. The processes of digestion include: ingestion, digestion, absorption, and elimination.
Ingestion begins in the mouth where your cheeseburger starts the journey through the digestive tract. Chemical digestion starts here, even before you took the first bite your mouth began to “water” just thinking about it. The water is a really thin-mucous fluid that is secreted by the salivary glands called saliva. Saliva moistens the food and helps to break down food into smaller pieces. Within the fluid is an enzyme called salivary amylase. This enzyme helps to break down starches (carbohydrates) to simple sugars, like that piece of lettuce, the pineapple, and that bun. In the mouth we also have mechanical digestion; this involves the teeth and the tongue. Teeth are used for chewing the food into smaller pieces and the tongue to help guide the food into the esophagus. After chemical and mechanical digestion the food becomes a bolus (food ball) and swallowed. The bolus passes the epiglottis which is a flap that closes over the trachea to prevent the bolus from entering the lungs.
Next the bolus enters the esophagus; this is one big drop down to the stomach. The esophagus (food pipe) moves the bolus down by means of peristalsis; a muscle action. The back and forth motion aids in mixing. The muscle action can help break down the size of the foodstuff. At the end of the esophagus is the cardiac sphincter which is the opening into the stomach. The sphincter controls the movement of the bolus from the esophagus to the stomach but also prevents the acid of the stomach from entering the esophagus.
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