What is the main function of the small intestine?(use terms : villi, surface area, blood capillaries, why must large molecules be broken down, high concentration and low concentration.)

Among the principal functions of the small intestine, we might mention the peristaltic movement, secretion through special glandules, digestive function, absorptive functions, secretion functions, and endocrine functions.

Explanation:  

The whole digestive tube is approximately eleven meters long, from the mouth to the anus.

The small or thin intestine is the longest organ of the digestive tube. It can reach up to 7 meters long, up to 3 centimeters in diameter, and it characterizes by being folded. These folds are called villi, they project into the intestine light, and they are more concentrated in the first portion of the intestine, the duodene, decreasing to the final region of the organ.

Among the principal functions of the small intestine, we might mention the peristaltic movement, secretion through special glandules, digestive function, absorptive functions, secretion functions, and endocrine functions.

The small intestine receives food from the stomach, and through peristaltic movements, it mixes and carries the material to different regions in the organ. The complex polymeric molecules are digested and transformed into simpler substances. The duodene receives secretions from intestinal glands such as bile and pancreatic juices and mixes them with digestive juices of its production. All of these secretions carry huge amounts of enzymes that will degrade food and transform it into soluble substances, such as amino acids. The intestine walls are covered by villi that increase the absorption surface area. Nutrients are absorbed by primary cells and transported to the bloodstream. Calciform cells secrete mucus to protect the epithelium during digestion. Villi also transport water from the blood to the intestinal tract, which helps in food decomposition. Enteroendocrine cells secrete hormones to the blood vessels and capillaries that enter each villus. When nutrients are small enough they go to enter the bloodstream.

Peyer's patches are nodules or cumulus of lymphatic tissue and other accessory cells, located under the mucosa of the gastrointestinal tract, specifically in the lamina propria of the thin intestine, in the jejunum region. These patches represent the mucosa´s immunity system. In the jejunum, these follicles are isolated from each other in the intestine and low concentrated. But in the terminal ileum (The last portion of the thin intestine) they get so close that they might form a plaque.