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Physiology of the alimentary tract

The first step in the alimentary system can begin before the food is in your mouth. When you smell or see food, you start to salivate, thus beginning the digestive process.

Food is the body's source of fuel. Nutrients in food give the body's cells the energy they need to operate. Before food can be used, it has to be broken down into tiny pieces. Then it is easy to absorb by the body. In humans, proteins are broken down into amino acids, starches into sugars, and fats into fatty acids and glycerol.

During digestion two main processes occur at the same time:

· Mechanical Digestion: larger pieces of food break down into smaller pieces before the chemical digestion. Mechanical digestion starts in the mouth and continues in to the stomach.

· Chemical Digestion: several different enzymes break down macromolecules into smaller molecules. They are absorbed more efficiently. Chemical digestion starts with saliva and continues into the intestines.

In the alimentary tract the food really passes through the body rather than being in the body. The smooth muscles of the tubular digestive organs move the food efficiently along as it is broken down into absorb-able atoms and molecules. During absorption, the nutrients that come from food (such as proteins, fats, carbohydrates, vitamins, and minerals) pass through the wall of the small intestine and into the bloodstream and lymph. In this way nutrients are distributed throughout the rest of the body. In the large intestine there is re-absorption of water and absorption of some minerals and feces are formed.

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