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The Digestive System The Digestive System is composed of 5 main parts. They are: 1) The Mouth 2) The Esophagus 3) The Stomach 4) The Small Intestine 5) The Large Intestine The Mouth This is where digestion first begins in the body The teeth perform physical digestion by breaking the food into smaller pieces The enzyme amylase performs chemical digestion by breaking down starch to sugar The Esophagus The esophagus is a tube of smooth muscle that connects the mouth to the stomach It is about 25 cm long Food moves through the esophagus by the process of peristalsis No digestion occurs in the esophagus The Stomach The stomach is like a muscular bag – It contracts rhythmically to mix the contents It contains gastric juice which is a mixture of hydrochloric acid and enzymes The acid kills invading pathogens on the food we eat It has a thick mucus layer to withstand the acid The entrance to the stomach is controlled by the cardiac sphincter, the exit by the pyloric sphincter The Small Intestine The small intestine is composed of 3 parts: the duodenum, the jejenum, and the ileum It is about 6m long 6 enzymes present: Erepsin and enterokinase to digest protein; maltase, sucrase, and lactase to digest sugars; and lipase to digest fat Small Intestine continued… The inner membrane of the small intestine is highly folded into tiny, finger-like projections called villi The villi greatly increase the surface area available for nutrient absorption The Large Intestine No digestion occurs in the large intestine The main job of the large intestine is to reabsorb water to prevent dehydration Other Structures Involved in Digestion The Liver: The largest gland in the body, the liver produces bile to emulsify fats. It stores energy, iron, and vitamins A, D, and B12 The Pancreas: The pancreas produces pancreatic juice which contains 28 enzymes. This juice also neutralizes the stomach acid to prevent damage to the small intestine. It also produces insulin to help regulate blood sugar Other Structures continued… Gall Bladder: The gall bladder stores the bile produced by the liver until it is ready to be released