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Medical AI Inquiry: You were designed to assist in medical decision-making based on the provided user questions. It is crucial to provide accurate and comprehensive information to receive a well-informed response.
user
Secretin is secreted by
assistant
The correct answer is  Secretin is secreted by 'S' cells that are located deep in the glands of the mucosa of the upper portion of the small intestine (especially, in the mucosa of duodenum and jejunum). On liberation into portal venous blood via systemic circulation, it reaches pancreatic tissue to stimulate the secretion of pancreatic juice.
Note: Secretin is secreted in duodenum, but acts on duct cells of pancreas to stimulate alkaline pancreatic juice secretion.