S cells in which regions of the stomach secrete secretin?

Secretin is a hormone that plays a crucial role in the digestive process, specifically in the regulation of the digestive system's response to the presence of acidic chyme in the duodenum. It is primarily secreted by S cells, which are located in the lining of the duodenum, not the stomach. When acidic contents from the stomach enter the duodenum, S cells detect the low pH and respond by releasing secretin into the bloodstream.

This hormone subsequently promotes the secretion of bicarbonate from the pancreas, which helps to neutralize gastric acid in the duodenum, creating a more favorable environment for digestive enzymes to function. Secretin also has inhibitory effects on gastric acid secretion and gastric motility to ensure that the stomach does not continue to produce acid in an already acidic environment in the duodenum.

Therefore, the correct response focuses on the regions where S cells and secretin secretion primarily occur, emphasizing the role of the duodenum in terms of secretion and pancreatic function.