십이지장, or the duodenum, is the first part of the small intestine in the human digestive system. It connects the stomach to the jejunum and plays a crucial role in digestion by receiving partially digested food, bile from the liver, and pancreatic juices. This combination helps break down food further for nutrient absorption. The name "십이지장" means "twelve finger widths" in Korean, reflecting its length, which is approximately 25 to 30 centimeters. It is divided into four sections: the superior, descending, horizontal, and ascending parts, each contributing to the digestive process and preparing food for the next stage in the small intestine.