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What are the stages of digestion?

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Quick Answer

The stages of digestion in a human being are the cephalic phase, the gastric phase and the intestinal phase. During these phases, nutrients are broken down to provide fuel for the body.

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Full Answer

The cephalic phase begins even before food is eaten. The digestive mechanism is stimulated simply by the sight, smell or even the thought of food. Digestion properly begins when the food is in the mouth and chewed, or masticated. As it's being ground down, it's moistened with saliva, which contains enzymes that change some carbohydrates into sugar.

The food is swallowed, and then travels down the esophagus to the stomach. This begins the gastric phase. In the stomach, the food is churned and bathed in gastric juices, which are mainly made up of pepsin and hydrochloric acid. Gastric juices begin the digestion of proteins and change the food into a slurry called chyme. Chyme then passes from the stomach, through the duodenum and into the small intestine.

This is when the intestinal phase begins. Digestion is mostly completed in the small intestine through the action of bile and intestinal and pancreatic juices. Pancreatic juice is made of enzymes that break down partially digested proteins, carbohydrates and fats. Bile also helps in the digestion of fats.

The part of the meal that's undigestable passes into the large intestine, which absorbs water and minerals. It then passes out of the body in the form of feces.

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