Despite its small size, the duodenum is a massively important part of the human digestive system. The C-shaped organ, the first portion of of the small intestine, acts as the bridge between the stomach and the larger small intestine, and works in tandem with the gallbladder, liver, and pancreas to prepare digested food for the rest of the digestive process. Though it's the shortest part of the intestinal tract, without healthy duodenum function digestion can take significantly longer – or become an incredibly painful process.
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The duodenum, as the chamber connecting the stomach to the rest of the intestinal tract, functions as a processing plant for the mostly digested food (called chyme) and stomach acids coming from the stomach. The organ, with fluids secreted by the gallbladder, liver, and pancreas, neutralizes stomach acid and breaks down chyme into a state where nutrients can easily be extracted from it. The duodenum then passes the chyme into the jejunum – the next part of the small intestine, but not before absorbing iron and a few other vitamins from the processed chyme.
The duodenum's location is just beneath the stomach, and sits to the right of the body. It measures about 12 inches long, and is connected not only to the stomach and the jejunum – the second part of the small intestine – but to the gallbladder, liver, and pancreas as well, through an orifice known as the ampulla of Vater, which sits to the center of the duodenum.
The duodenum is crucial to small intestine function in the digestive system as a whole, because it is where chyme – the mix of mostly-digested food and stomach acid – is processed. When chyme from the stomach enters the duodenum, the intestinal organ begins to secrete a mucus that neutralizes stomach acid, preventing it from harming the more sensitive parts of the intestinal tract. It then pushes chyme towards the ampulla of Vater, where the chyme is mixed with pancreatic juices and bile from the liver and gallbladder. These bodily fluids process the chyme, breaking down the chemical compounds present so that nutrients can more easily be extracted as it passes through the intestines. Once this process is complete, the chyme is shuffled towards the jejunum to have nutrients pulled from it.
However, the duodenum does more than just process chyme for the rest of the digestive tract. As it sends processed chyme to the jejunum, the duodenum absorbs some nutrients: the most important of these are iron – but the organ also takes in vitamins A and B1, calcium, fatty and amino acids, among other nutrients. Because of this, those who have had duodenum bypass surgery must take iron supplements to stay healthy.