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Why Must Digestion Break Down Large Molecules?

By Lexa W. Lee ; Updated August 14, 2017

Digestion is the process of breaking large molecules of food into ever smaller molecules. As food moves from your mouth and on through your digestive tract, it is chewed, churned, pushed and mixed with digestive enzymes that break it down into various nutrients and building blocks that your body requires.

How It Works

Digestion is necessary in order to reduce food to small enough molecules that your intestinal tract can absorb and release into the blood, where they are then transported to cells throughout your body. The mechanical breakdown of food into smaller pieces also allows digestive enzymes to reach and digest them more completely. When you have diarrhea, undigested food and unabsorbed water pass out of your digestive tract, resulting in the loss of nutrients.

Mechanical Breakdown of Food

The movement of food in the digestive tract aids in the mechanical breakdown of food. While chewing and swallowing are voluntary movements, after you swallow the food, the motions involved in digestion are involuntary and automatic. Your nervous system controls these motions. Peristalsis refers to the wavelike muscular motion that propels food through the tract and also mixes the contents in each organ. Your stomach's muscular movements actively mix food and enzymes, and sphincter muscles control the release of food from one digestive organ to the next.

Digestive Enzymes

The process of digestion involves many enzymes that break down different nutrients. For example, your salivary glands produce amylase, which acts on starch; your stomach produces hydrochloric acid and an enzyme that digests protein; your small intestine produces more enzymes for starch, protein and fat; your liver makes bile, which helps dissolve fat. During digestion, the chemical bonds linking the building blocks of proteins, carbohydrates and fats are broken, releasing energy.

Additional Information

The breakdown process in digestion is called catabolism. The absorption of food molecules takes place primarily in the large intestine. Your body can use the smaller molecules to build its own different proteins, carbohydrates and fat as needed. The building process is called anabolism. The various constituents of food, as well as vitamins and minerals, are required for normal growth, development and repair of your body, as well as energy production, energy storage, and other metabolic processes.

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