Respuesta :
Answer:
Secretion of pancreatic fluid can be divided into three phases which correspond to the different stages of food ingestion. Each phase tends to induce a slightly different composition of pancreatic secretion with slightly different regulatory mechanisms. Cephalic Phase
This phase is initiated by the sensory experience of seeing and eating food and primarily involves vagus nerve stimulation of acinar cells to produce digestive enzymes. Because little aqueous sodium bicarbonate solution by ductal cells these enzymes lie inactive within the pancreatic acini and ducts.
Gastric Phase
This phase is initiated by the presence of food within the stomach and is once again primarily involves vagus nerve stimulation of acinar cells to produce digestive enzymes. By the end of the cephalic and gastric phases, the pancreatic ducts are filled with inactive digestive zymogens ready for washing out into the intestinal lumen by aquous sodium bicarbonate solution.
Intestinal Phase
This phase is initiated by emptying of stomach contents into the small Intestine and involves release of both secretin and cholecystokinin which stimulate pancreatic ductal cells to synthesize aqueous sodium bicarbonate solution. The generation of aqueous sodium bicarbonate solution washes out all of the inactive pancreatic enzymes waiting within the pancreatic ducts into the duodenum where they activated as discussed previously.
Explanation:
The exocrine pancreas secretes an aqueous mixture into the duodenum composed of digestive enzymes, which aid in further degradation of ingested food, and bicarbonate which helps neutralize stomach acid. Neutralization of gastric acid is a critical function of the pancreas as the small intestine mucosa is specialized for nutrient absorption and thus cannot possess a thick protective mucous layer similar to that of the stomach. Furthermore, pancreatic digestive enzymes are optimally active at basic pHs and thus pancreatic bicarbonate secretion is a key requirement for proper digestion.
