Though they are truly inferior in size to the large intestines, the small intestines play a huge role in the digestion and absorption of the nutrients we feed our bodies. The small intestines are coiled in the abdomen and are surrounded by a large network of blood vessels. Because of the peristaltic movements (repetitive, wave-like motion) of the digestive tract, there is some mechanical breakdown of food in the small intestine; however, the main role it plays is in the absorption of nutrients from the food we eat. This organ is about 1 inch in diameter and approximately 20 feet in length. It is divided into three sections; the duodenum, the jejunum, and the ileum; each with its distinctive function.
The duodenum is the first part of the small intestine and is attached to the end of the stomach. At only 10 inches, it is the smallest of the three sections, and is primarily responsible for the chemical digestion of food. The duodenum contains mucous and hormone secreting glands, and both the pancreatic and the bile ducts enter the duodenum, where they empty their digestive juices. The compilation of digestive juices in this part of the small intestine is responsible for the further digestion of fats, protein, and starch.
The jejunem is the middle of the three divisions of the small intestine. It is approximately eight feet in length, and contains folds called plicae circulars. Arising from these folds are the villi and the microvilli, tiny finger-like projections that protrude from the walls of the small intestine. These function together to increase the surface area available to secrete enzymes and absorb nutrients from our dietary intake. It has been estimated that the surface area of the small intestine is about 200m2, or the floor space of an average two-story house.
The ileum is the last section of the small intestine, following the jejunum, and connects the small intestine to the large. It is approximately 12 feet in length, and functions primarily to absorb vitamin B12 and bile salts. The enzymes necessary for the final digestion of protein and carbohydrates are secreted here. Villi and microvilli also line the ileum, so anything not absorbed by the jejunum is available to the ileum. The ileum is also distinguishable from the other sections of the small intestine by the Peyer’s patches—lymphoid nodules containing a large amount of lymphocytes and other cells important to the immune system. Because the inside of the gastrointestinal tract is exposed to the external environment, much of it is populated with disease-causing organisms. These patches establish their importance in the immune system surveillance of the intestines and help in generating an immune response, if necessary.
It is quite obvious that the small intestines are important to the body’s overall health. Since the small intestine is dependent upon the food that we put into it, the status of our health depends largely on the quality of food that we put into our bodies. Be kind to your body, and it will be kind to you.