The Small Intestines begin after the stomach at the pyloric sphincter (upper junction between stomach and small intestines) and continue in twisted convoluted shape to the ileocecal valve (lower junction between small intestines and large intestines).
The small intestines are 2.5 to 4 cm in diameter and approxiamtely 20 ft long. The length of the small intestines creates a massive surface area for the purpose of nutrient absorption. "One estimate is that the intestinal surface area is about equal to the floor space of an average two-story house!" (Human Anatomy & Physiology, Marieb, pg 909).
Holistic & Integrative Medicine