The Small Intestine
The small intestine, the coiled tube connecting the stomach to the large intestine that is responsible for most of the absorption of nutrients during digestion, is actually quite large. The average length is 23 feet and its surface area, after you account for its folds and the tiny villi and microvilli that project out from its walls, is nearly 2,700 square feet -- nearly the size of a tennis court!
The small intestine is divided up into three parts:
- The duodenum takes semi-digested, liquified food from the stomach and continues to break it down with enzymes and bile from the gallbladder, liver, and pancreas. Sodium bicarbonate also enters the digestive system here from the pancreas to neutralize stomach acids. Additionally, iron is absorbed into the body through this section of the intestines.
- The jejunum is the section where the majority of nutrient absorption -- and particularly that of proteins and carbohydrates -- takes place. Minerals, vitamins, water, fatty acids, amino acids, sugar, and electrolytes all are absorbed by the villi and seep into the blood vessels in the organ's walls, and flow into the blood stream to be carried off elsewhere in the body.
- The ileum is the section where Vitamin B12, bile salts, and any other undigested nutrients are absorbed by the villi and microvilli and sent into the blood stream. The ileum then forces any undigested waste matter into the large intestine for the final phases of the digestive process.
Learn more about the intestines and digestion with these Science NetLinks resources:
- Human Body App (K-5)
- Nutrition 1: Food and the Digestive System (3-5)
- Nutrition 3: Got Broccoli? (3-5)
- Systems of the Human Body (3-5)
- All Systems Are Go! (3-8)
- Alcohol's Effect on the Mind and Body (6-8)
- Appendix Purpose (6-12)
- Gut Stem Cells (6-12)
- M.S. and Gut Bacteria (6-12)
- Obesity: The Science Inside (6-12)
- Organs (6-12)