Most of the absorption occurs in small intestine
Most of the food a person consumes is digested and absorbed in the small intestine. The lining of the small intestine has tiny finger–shaped raised tissues (villi). These raised tissues greatly increase the surface area of the intestine, which absorbs calories and nutrients from food Small intestine is the part of gastrointestinal system where most of the digestion and absorption occurs.
The small intestine with a length of more than 6 m is the longest section of the alimentary canal. The name "small intestine" refers to its small diameter, compared with that of the large intestine. Most of the enzymatic hydrolysis of food macromolecules and most of the absorption of nutrients into the blood occur in the small intestine. The first 25 cm or so of the small intestine is called the duodenum where the acid chyme from the stomach mixes with digestive juices from the pancreas, liver, gallbladder and gland cells of the intestinal wall itself.
Virtually all nutrients from the diet are absorbed into blood across the mucosa of the small intestine. In addition, the intestine absorbs water and electrolytes, thus playing a critical role in maintenance of body water and acid–base balance. Hydrolytic enzymes from accessory glands mix with acid chyme in the duodenum, continuing the digestion process. This organ has a huge surface area of 300 m2, roughly the size of a tennis court. Large circular folds in the lining bear finger–like projections called villi, and each epithelial cell of a villus has many microscopic appendages called microvilli that are exposed to the intestinal lumen. The microvilli's shape is the basis of the term brush border for the intestinal epithelium. This enormous microvillar surface is an adaptation that greatly increases the rate of nutrient absorption.