What Is Pancreatic Juice?

Pancreatic juice generally refers to a colorless and odorless alkaline solution secreted by the human body from the exocrine portion of the pancreas. Adults secrete 750 to 1500 ml per day. The inorganic substances in pancreatic juice are mainly water and bicarbonate. Bicarbonate is secreted by the cells of the wall of the small duct of the pancreas. Its main role is to neutralize the gastric acid entering the duodenum, provide the most suitable alkaline environment for the activities of various digestive enzymes in the small intestine, and protect the intestinal mucosa from Attacked by acid. The organic matter in the pancreatic juice is a variety of digestive enzymes, which can act on three food ingredients, sugar, fat and protein, so it is the most important one in the digestive juice. Pancreatic amylase breaks down starch into maltose, and pancreatic maltase breaks down maltose into glucose. Pancreatic lipase breaks down neutral fat into glycerol and fatty acids.

The pancreas has both endocrine and exocrine functions. Endocrine function is mainly related to glucose metabolism. The exocrine secretion of the pancreas is pancreatic juice. Of all the digestive juices, its digestion is the strongest, with digestive enzymes that break down the three major nutrients ^[1]

Pancreatic juice is a colorless, odorless alkaline liquid with a pH of 7.8 to 8.4, an osmotic pressure equal to that of plasma, and an adult daily secretion of 1 to 2 L. The components of pancreatic juice include inorganic substances in addition to water, such as sodium ions, hydrogen ions, bicarbonate ions, etc .; organic substances are mainly various digestive enzymes ^[1]

In the non-digestive phase, pancreatic juice is scarcely secreted or secreted very little, and the secretion of pancreatic juice increases after eating. Food is a natural stimulus for pancreatic juice secretion. Pancreatic fluid secretion is regulated by nerve and humoral factors, but mainly humoral regulation.
1. The shape, smell, and stimulation of foods on the receptors of the mouth, pharynx, esophagus, and gastrointestinal tract can cause pancreatic fluid secretion through conditioned and unconditioned reflex. The reflex efferent nerve is mainly the vagus nerve, and its peripheral end releases acetylcholine, which mainly acts on pancreatic acinar cells and has a weak effect on pancreatic ductal cells. Therefore, when the vagus nerve is excited, less water and bicarbonate are secreted, and pancreatin is higher.

2. Humoral regulation (1) Secretin is a peptide hormone secreted by S cells from the upper mucosa of the small intestine. The strongest secreting stimulant is hydrochloric acid, followed by protein breakdown products and fatty acids. Sugars have no stimulating effect. Secretin acts on pancreatic ductal epithelial cells through blood circulation, causing a large amount of pancreatic juice secretion, in which the content of water and bicarbonate is high, and the content of pancreatin is low.
(2) Cholecystokinin (CCK), also known as trypsin, is a peptide hormone secreted by small cells of the small intestine. Protein breakdown products, fatty acids, hydrochloric acid and fat can all stimulate its secretion, but sugars have no stimulating effect. CCK physiological effects: Act on pancreatic acinar cells, and promote the secretion of pancreatic enzymes in pancreatic juice (hence the name pancreatin). stimulate the gallbladder to contract and expel bile. Promote the synthesis of protein and ribonucleic acid in pancreatic tissue, and have nutritional effects on pancreatic tissue.
Secretin and CCK have a synergistic effect on promoting secretion of the pancreas. In addition, gastrin can also promote pancreatin secretion. Vasoactive intestinal peptide can promote the secretion of water and bicarbonate in pancreatic juice, while glucagon, somatostatin, pancreatic polypeptide, and calcitonin gene-related peptide can all inhibit the secretion of pancreas.
3 Feedback regulation of pancreatic juice secretion. Recent studies have shown that protein breakdown products and fatty acids can stimulate the secretion of CCK-releasing peptide (CCK-RP) in the small intestinal mucosa. CCK-RP mediates the secretion of CCK by I cells, thereby promoting the secretion of pancreatic enzymes. Promote the inactivation of CCK-RP, thereby feedback-inhibiting the secretion of CCK and pancreatin. Its significance is to prevent pancreatic enzyme secretion through negative feedback regulation ^[1] .