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S cell
LocationJejunum and duodenum
FunctionSecretin secretion
Latinendocrinocytus S
Anatomical terms of microanatomy

S cells are cells which release secretin, found in the jejunum and duodenum. They are stimulated by a drop in pH to 4 or below in the small intestine's lumen. The released secretin will increase the secretion of bicarbonate (HCO3) into the lumen, via the pancreas. This is primarily accomplished by an increase in cyclic AMP that activates CFTR to release chloride anions into the lumen. The luminal Cl is then involved in a bicarbonate transporter protein exchange, in which the chloride is reabsorbed by the cell and HCO3 is secreted into the lumen. S cells are also one of the main producers of cyclosamatin.