Digestive System Small Intestine

Stimulates the pancreas to release of sodium bicarbonate

Pancreas

Secretin

Fundamnetals:

• Stimulated by from low duodenal pH (2-4.5)
  • Also the secretion of secretin is increased by the products of protein digestion bathing the mucosa
  • Also bile salts and fatty acids
  • Oligopeptide stimulated

Function/Purpose:

• Target organ Pancreas
  • Secrete bicarbonate
• Enhances CCK's function

LOC:

• Small intestine - duodenum

Additional Information:

    Secretin is a hormone that causes pancreatic juice to be excluded from the pancreas
        When hydrochloric acid passes from the stomach into the duodenum, secretin is released into the bloodstream and stimulates the acinar cells of the pancreas to secrete water and bicarbonate into the pancreatic ducts that drain into the duodenum. By this mechanism, hydrochloric acid secreted by the stomach, which can be damaging to the intestinal lining, is promptly diluted and neutralized. Secretin also inhibits the secretion of gastrin, which triggers the initial release of hydrochloric acid into the stomach, and delays gastric emptying.
''Molecular basis''
    Secretin increases watery bicarbonate solution from pancreatic duct epithelium. Pancreatic acinar cells have secretin receptors in their plasma membrane. As secretin binds to these receptors, it stimulates adenylate cyclase activity and converts ATP to cyclic AMP. Cyclic AMP acts as second messenger in intracellular signal transduction and leads to increase in release of watery carbonate. It is known to promote the normal growth and maintenance of the pancreas.
    It counteracts blood glucose concentration spikes by triggering increased insulin release from pancreas, following oral glucose intake.
  
    Although secretin releases gastrin from gastrinomas, it inhibits gastrin release from the normal stomach. It reduces acid secretion from the stomach by inhibiting gastrin release from G cells. This helps neutralize the pH of the digestive products entering the duodenum from the stomach, as digestive enzymes from the pancreas (e.g., pancreatic amylase and pancreatic lipase) function optimally at slightly basic pH.[citation needed]
    In addition, secretin stimulates pepsin secretion from chief cells, which can help break down proteins in food digestion. It also stimulates release of glucagon, pancreatic polypeptide and somatostatin.