What Does the Small Intestine Do in the Digestive System?

In the digestive system, the small intestine does several specialized functions to process food and convert it to usable energy for the body.

The small intestine is a muscular tube that can measure up to 22 feet in length, explains Cleveland Clinic, and its main function is to continuously break down food and absorb nutrients before waste is passed into the large intestine.

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Food that enters the small intestine from the esophagus continues its journey through the digestive tract by means of involuntary, rhythmic muscular contractions called peristalsis. Different types of nutrients are absorbed in different areas of the small intestine and by different means.

The small intestine is made up of three parts: the duodenum, the jejunum, and the ileum. The lining of the small intestine is covered in folds of finger-like tissues called villi that increase the total surface area for maximum nutrient absorption.

According to the Gastroenterology Society of Australia, the duodenum receives the partially-digested food and acids from the stomach where the alkaline environment quickly neutralizes it. Here, the food is mixed with digestive enzymes, bile, and secretions from the pancreas.

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Most absorption of fats, proteins, and carbohydrates occurs in the duodenum before the food moves into the jejunum and ileum. In these final two portions of the small intestine, food is broken down into much smaller nutrient components. It is here that the abundant surface area created by the villi absorb amino acids, fatty acids, cholesterol, minerals, vitamins, and salts.

The small intestine is the powerhouse of the digestive system. News Medical explains that about 90 percent of all nutrient absorption occurs in the small intestine, and about 80 percent of all water is absorbed by the time the remaining food and undigested solids are passed to the large intestine primarily as solid waste.

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