Both the stomach and duodenum are parts of the digestive system. Food enters the stomach first, where it is partially processed, and it then travels into the duodenum, the first portion of the small intestine. The duodenum is the first location in the body to absorb nutrients from the food, once the stomach breaks it down in a preparatory step.
The function of the stomach is to be a collection area for food, and to add acid to the food to help it break down. To accommodate an entire meal, the stomach is expandable. Basically, it is a large pouch that has an outer covering of muscle that can shrink and expand the stomach to help mash up food. To speed up the breakdown of food, the stomach also produces substances like stomach acid and enzymes. As well as releasing substances inside the stomach pouch, the organ also sends biological signals to the brain to indicate whether a person is full or hungry.
In the digestive tract, the stomach and duodenum are attached, and the stomach is first. The duodenum is part of the small intestine, and is followed by the jejunum and the ileum. It is the point where the body absorbs all the broken down components of the food, for use in the rest of the body. The Latin word duodenarius which means "twelve," is the origin of the word duodenum, as the distance from the start to the end of this part of the digestive system is about 12 finger widths long. The stomach and the duodenum are separated by a muscular area at the end of the stomach called the pylorus.
As food in the stomach needs processing before entering the next step in digestion, the duodenum, a type of biological gateway is necessary. This gateway between the stomach and duodenum is the pylorus, which contracts and expands to push food onward into the duodenum. The pyloric sphincter is a tight muscular ring that blocks the food from getting back into the stomach.
When food moves between the stomach and duodenum it is very acidic. Substances that are alkaline enter into the duodenum to give the food a neutral pH. The small digestive organs the gallbladder and the pancreas produce these alkaline compounds along with more substances that can digest food even further. The body can then absorb nutrients through the wall of the duodenum, and this continues further along the small intestine.