S cell

{{for|the cell cycle phase|S phase}}

{{Infobox cell

| Name = S cell

| Latin = endocrinocytus S

| Image =

| Caption =

| Image2 =

| Caption2 =

| Precursor =

| System =

| Location = Jejunum and duodenum

| Function = Secretin secretion

}}

S cells or Secretin cells are cells which release secretin, found in the jejunum and duodenum.{{Cite journal |last1=Afroze |first1=Syeda |last2=Meng |first2=Fanyin |last3=Jensen |first3=Kendal |last4=McDaniel |first4=Kelly |last5=Rahal |first5=Kinan |last6=Onori |first6=Paolo |last7=Gaudio |first7=Eugenio |last8=Alpini |first8=Gianfranco |last9=Glaser |first9=Shannon S. |date=October 2013 |title=The physiological roles of secretin and its receptor |journal=Annals of Translational Medicine |volume=1 |issue=3 |pages=29 |doi=10.3978/j.issn.2305-5839.2012.12.01 |issn=2305-5839 |pmc=4200670 |pmid=25332973}} 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.

File:Secretin cells in the duodenum of (A) a healthy subject, (B) a patient with celiac disease (CD), and (C) a patient with irritable bowel syndrome (IBS) 1.jpg (CD), and (C) a patient with irritable bowel syndrome (IBS)]]