After food moves from the stomach to the duodenum, the first section of the small intestine, it combines with bile from the gall bladder and digestive juices from the pancreas. The intestines contract and relax through peristaltic action to mix these substances with food to promote digestion.
In the duodenum, nutrients from food, especially iron and calcium, begin to be absorbed into the body. Iron must have an acidic environment for proper absorption. Antacid medications hinder this process. If too little iron is absorbed, it can cause anemia. If calcium intake is low, its absorption begins in the duodenum. Vitamin D is needed for this to occur.