|
Digestion The digestive system can be looked at from many of the jobs taking place in it, all of which will be discussed here. The simplest way to look at the digestive system is by concentrating on the anatomical sites which can be separated into the alimentary canal and the accessory organs. The alimentary canal is the path the things you eat and drink take from the time the enter your body until the time they leave it. Digestion takes place in most of the alimentary canal through the use of enzymes that are secreted by accessory glands. Mouth - Physical breakdown begins here with chewing. The teeth and tongue are used at this stage to collect the food into a ball called a bolus. The digestion of starches begins here with the help of salivary amylase this is secreted from the salivary glands. The salivary glands also secrete water and mucus that are helpful in forming and moistening the bolus. Collectively, the substance secreted by the salivary glands is called saliva. Esophagus - The esophagus is a simple passageway for the bolus from the mouth to the stomach. Stomach - The stomach, with an acidic pH of 1-2, kills germs with its high acidity and further breaks down the bolus. Gastric glands, located in the walls of the stomach, secrete hydrochloric acid (HCl), responsible for the low pH, and pepsinogen, an inactive enzyme that reacts with the acid and becomes an enzyme that helps in the breakdown of protein. Ulcers form when the mucus lining of the stomach is insufficient and the acid and enzymes damage the stomach walls. The food, now a mushy substance called chyme, then enters the small intestine. Small Intestine - Bile, produced in the liver and stored and concentrated in the gallbladder, as well as many enzymes secreted by the pancreas, react with the chyme in the small intestine. Bile works to break down fats by physical, not chemical, means. The pancreas secretes amylase to digest carbohydrates, lipases for fats and proteases for protein. Bicarbonate is also secreted by the pancreas, a basic substance, which neutralizes the acidity of the chyme to allow the enzymes to work. Internal folds inside the small intestine greatly increase the surface area allowing nutrient absorption to occur. Large Intestine - The chyme at this point as finished digesting and the large intestine, also known as the colon, absorbs water before excreting the feces. |