# Duodenum --- The **duodenum** is part of the [[gastrointestinal tract|upper GI tract]], and is the first part of the [[small intestine]], directly connected to the [[stomach]]. where a **major portion** of [[digestion|chemical digestion]] takes place. ![[duodenum stomach gallbladder pancreas.png]] When the acidic [[stomach|chyme]] hits the duodenum, it is sensed by chemoreceptors and triggers the production of: - [[cholecystokinin]] - [[secretin]] - [[gastric inhibitory peptide]] Together these work to release [[bile]] from the gallbladder and [[digestive enzymes]] and [[bicarbonate|bicarbonate (HCO3-)]] from the pancreas. These substances enter into the duodenum via the **hepatopancreatic sphincter**. The reason we need the bicarbonate is to neutralize the stomach acid, and allow the digestive enzymes to work. ___