A mixture of food, liquid and digestive juice called chyme enters the small intestine from the stomach and combines with secretions such as enzymes, bicarbonate and bile salts to further break down food, according to the International Foundation for Functional Gastrointestinal Disorders. These enzymes come from the liver and pancreas. Food digests in three distinct parts of the small intestine.
The International Foundation for Functional Gastrointestinal Disorders explains chyme goes into the first part of the small intestine, called the duodenum, where digestive secretions help digest fat and fat-soluble vitamins. Nutrients such as vitamins A, E, D and K get broken down by bile salts from the liver. Bicarbonate from the pancreas neutralizes stomach acid.
In the middle part of the small intestine, called the jejunum, 90 percent of nutrient absorption of vitamins, minerals, proteins and carbohydrates occurs, according to the International Foundation for Functional Gastrointestinal Disorders. The final part of the small intestine, called the ileum, digests water, bile salts and vitamin B-12 before the remainder of food goes to the large intestine.
The National Institute of Diabetes and Digestive and Kidney Diseases indicates bacteria in the small intestines also produce enzymes that help digest carbohydrates. Starches are converted to usable glucose molecules in the small intestine. Once these nutrients are completely broken down, tiny strands of tissue called microvilli that line the small intestine absorb necessary chemicals directly into the blood through minuscule blood vessels called capillaries, according to the BBC.